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Por favor, deshabilite su bloqueador de anuncios (o actualice sus configuraciones para asegurarse de que se habilitan javascript y cookies), para que podamos seguir proporcionándole las noticias de primera clase del mercado. Y los datos que has llegado a esperar de nosotros. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Dimensión 3 IDEAS DEL CORAZÓN DISCIPLINARIO CIENCIAS FÍSICAS La mayoría de los sistemas o procesos dependen de algún nivel de subprocesos físicos y químicos que se producen dentro de él, ya sea que el sistema en cuestión sea una estrella, la Tierra subyace a todos los fenómenos naturales y huma - nanciados, Tales como los facilitados por el código genético o comunicados entre organismos, también pueden ser críticos para entender su comportamiento. Una meta general para el aprendizaje en las ciencias físicas, por lo tanto, es ayudar a los estudiantes a ver que hay mecanismos de causa y efecto en todos los sistemas y procesos que pueden ser entendidos a través de un conjunto común de principios físicos y químicos. El comité desarrolló cuatro ideas básicas en las ciencias físicas, tres de las cuales son paralelas a las identificadas en documentos anteriores, incluyendo los Estándares Nacionales de Educación Científica y Puntos de Referencia para la Alfabetización Científica. Las tres ideas principales son PS1: Materia e Interacciones, PS2: Movimiento y Estabilidad: Fuerzas e Interacciones, y PS3: Energía. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. También introducimos una cuarta idea central: PS4: Las ondas y sus aplicaciones en las tecnologías para la transferencia de información. Comprender la luz y el sonido como mecanismos de transferencia de energía (ver LS3) y transferencia de información entre objetos que no están en contacto. La comunicación moderna, la información y las tecnologías de imagen son aplicaciones de comprensión científica de luz y sonido y sus interacciones con la materia. Son penetrantes en nuestras vidas hoy y son también herramientas críticas sin las cuales gran parte de la ciencia moderna no podría ser hecha. Vea el recuadro 5-1 para un resumen de estas cuatro ideas principales y sus componentes. Las tres primeras ideas fundamentales de las ciencias físicas responden a dos preguntas fundamentales: las habilidades para concebir las interacciones de la materia y la energía son fundamentales para su educación científica. La división histórica entre los dos temas de la física y la química es trascendida en la ciencia moderna, ya que los mismos principios físicos se ven aplican desde escalas subatómicas a la escala del universo mismo. Por esta razón hemos elegido presentar los dos temas juntos, asegurando así un acercamiento más coherente a las ideas centrales a través de todos los grados. La designación de cursos de ciencias físicas en el nivel de secundaria como física o química no está excluida por nuestro agrupamiento de estas disciplinas lo que es importante es que a todos los estudiantes se les ofrece una secuencia de cursos que les da la oportunidad y el apoyo para aprender sobre todas estas ideas Y reconocer las conexiones entre ellos. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. IDENTIFICACIÓN DE LOS ASPECTOS BÁSICOS Y COMPONENTES EN LAS CIENCIAS FÍSICAS Idea central PS1: la materia y sus interacciones PS1.A: Estructura y propiedades de la materia PS1.B: Reacciones químicas PS1.C: Procesos nucleares Idea central PS2: Movimiento y estabilidad: Fuerzas e interacciones PS2. A: Fuerzas y Movimiento PS2.B: Tipos de Interacciones PS2.C: Estabilidad e Inestabilidad en Sistemas Físicos Idea Principal PS3: Energía PS3.A: Definiciones de Energía PS3.B: Conservación de Energía y Transferencia de Energía PS3.C: Relación entre Energía y Fuerzas PS3.D: Energía en Procesos Químicos y Vida cotidiana Idea central PS4: Ondas y sus Aplicaciones en Tecnologías para Transferencia de Información PS4.A: Propiedades de Onda PS4.B: Radiación Electromagnética PS4.C: Tecnologías de la Información e Instrumentación Citación Sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. La existencia de los átomos, ahora apoyada por la evidencia de los instrumentos modernos, se postuló primero como un modelo que podría explicar tanto las observaciones cualitativas como las cuantitativas sobre la materia (por ejemplo, el movimiento browniano , Relaciones de reactivos y productos en reacciones químicas). La materia puede entenderse en términos de los tipos de átomos presentes y de las interacciones entre ellos y dentro de ellos. Los estados (es decir, sólido, líquido, gas o plasma), las propiedades (por ejemplo, dureza, conductividad) y las reacciones (tanto físicas como químicas) de la materia pueden describirse y predecirse sobre la base de los tipos, interacciones y movimientos de los átomos dentro eso. Las reacciones químicas, que subyacen a tantos fenómenos observados en sistemas vivos y no vivos, conservan el número de átomos de cada tipo, pero cambian su disposición en moléculas. Las reacciones nucleares implican cambios en los tipos de núcleos atómicos presentes y son fundamentales para la liberación de energía del sol y el equilibrio de los isótopos en la materia. PS1.A: ESTRUCTURA Y PROPIEDADES DE LA MATERIA ¿Cómo se combinan las partículas para formar la variedad de materia que se observa? Aunque son demasiado pequeñas para ser vistas con luz visible, los átomos tienen sus propias subestructuras. Tienen una pequeña región central o núcleo diferentes isótopos del mismo elemento difieren en el número de neutrones solamente. A pesar de la inmensa variación y el número de sustancias, hay sólo unos 100 elementos estables diferentes. Cada elemento tiene propiedades químicas características. La tabla periódica, una representación sistemática de elementos conocidos, se organiza horizontalmente aumentando el número atómico y verticalmente por familias de elementos con propiedades químicas relacionadas. El desarrollo de la tabla periódica (que ocurrió mucho antes de entender la subestructura atómica) fue un avance importante, ya que sus patrones sugirieron y condujeron a la identificación de elementos adicionales con propiedades particulares. Además, los patrones de electrones más externos de la tabla, que desempeñan un papel importante en la explicación de la reactividad química y la formación de enlaces, y la tabla periódica sigue siendo una forma útil de organizar esta información. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. La subestructura de los átomos determina cómo se combinan y reorganizan para formar todas las sustancias del mundo. Las atracciones eléctricas y las repulsiones entre las partículas cargadas (es decir, los núcleos y electrones atómicos) en la materia explican la estructura de los átomos y las fuerzas entre los átomos que los hacen formar moléculas (a través de enlaces químicos) que varían en tamaño de dos a miles de átomos En moléculas biológicas tales como proteínas). Los átomos también se combinan debido a estas fuerzas para formar estructuras extendidas, tales como cristales o metales. Las propiedades variadas (por ejemplo, la dureza, la conductividad) de los materiales que se encuentran, tanto naturales como fabricados, se pueden entender en términos de los constituyentes atómicos y moleculares presentes y las fuerzas dentro y entre ellos. Dentro de la materia, los átomos y sus constituyentes están constantemente en movimiento. La disposición y el movimiento de los átomos varían de formas características, dependiendo de la sustancia y su estado actual (por ejemplo, sólido, líquido). La composición química, la temperatura y la presión afectan a tales arreglos y movimientos de átomos, así como las formas en que interactúan. En un conjunto dado de condiciones, el estado y algunas propiedades (por ejemplo densidad, elasticidad, viscosidad) son los mismos para diferentes cantidades en masa de una sustancia, mientras que otras propiedades (por ejemplo, volumen, masa) proporcionan medidas del tamaño de la muestra a mano . Los materiales pueden caracterizarse por sus propiedades medibles intensivas. Diferentes materiales con diferentes propiedades se adaptan a diferentes usos. La capacidad de imagen y manipular la colocación de átomos individuales en estructuras diminutas permite el diseño de nuevos tipos de materiales con particular funcionalidad deseada (por ejemplo, plásticos, nanopartículas). Además, la explicación moderna de cómo determinados átomos influyen en las propiedades de los materiales o moléculas es crítica para comprender el funcionamiento físico y químico de los sistemas biológicos. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación científica de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Puntos finales de la banda de grado para PS1.A Al final del grado 2. Existen diferentes tipos de materia (por ejemplo, madera, metal, agua), y muchos de ellos pueden ser sólidos o líquidos, dependiendo de la temperatura. La materia puede ser descrita y clasificada por sus propiedades observables (por ejemplo, visual, auditivo, textural), por sus usos, y por si ocurre naturalmente o se fabrica. Diferentes propiedades son adecuadas para diferentes propósitos. Una gran variedad de objetos se pueden construir a partir de un pequeño conjunto de piezas (por ejemplo, bloques, conjuntos de construcción). Pueden pesarse objetos o muestras de una sustancia, y su tamaño puede ser descrito y medido. Al final del grado 5. La materia de cualquier tipo puede subdividirse en partículas que son demasiado pequeñas para ver, pero aún así la materia todavía existe y puede ser detectada por otros medios ( Por ejemplo por pesaje o por sus efectos sobre otros objetos). Por ejemplo, un modelo que muestra que los gases están hechos de partículas de materia que son demasiado pequeñas para ver y se mueven libremente en el espacio puede explicar muchas observaciones, incluyendo la inflación y la forma de un globo los efectos del aire en partículas o objetos más grandes Hojas en el viento, polvo suspendido en el aire) y la aparición de gotas de agua en la escala visible en la condensación, la niebla y, por extensión, también en las nubes o las estelas de un chorro. La cantidad (peso) de materia se conserva cuando cambia de forma, incluso en transiciones en las que parece desaparecer (por ejemplo, azúcar en solución, evaporación en un recipiente cerrado). Se pueden usar mediciones de una variedad de propiedades (por ejemplo, dureza, reflectividad) para identificar materiales particulares. (Límite: A este nivel de grado no se distinguen la masa y el peso y no se intenta definir las partículas invisibles ni explicar el mecanismo de evaporación y condensación a escala atómica). Al final del grado 8. Todas las sustancias están hechas de Unos 100 diferentes tipos de átomos, que se combinan entre sí de varias maneras. Los átomos forman moléculas que varían en tamaño de dos a miles de átomos. Las sustancias puras están hechas de un solo tipo de átomo o molécula, cada sustancia pura tiene propiedades físicas y químicas características (para cualquier cantidad en masa bajo condiciones dadas) que pueden usarse para identificarlo. Los gases y líquidos están hechos de moléculas o átomos inertes que se mueven unos con relación a otros. En un líquido, las moléculas están constantemente en contacto entre sí en un gas, están ampliamente espaciadas excepto cuando se producen chocan. En un sólido, los átomos están estrechamente espaciados y vibran en posición, pero no Sugerencias de Citación: 5 Dimensión 3: Disciplinario Core Ideas - Ciencias Físicas. Consejo nacional de investigación. Un marco para la educación científica de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Cambiar las ubicaciones relativas. Los sólidos pueden formarse a partir de moléculas, o pueden ser estructuras extendidas con subunidades repetitivas (por ejemplo cristales). Los cambios de estado que se producen con variaciones de temperatura o presión pueden describirse y predecirse utilizando estos modelos de materia. (Límite: Las predicciones aquí son cualitativas, no cuantitativas.) Al final del grado 12. Cada átomo tiene una subestructura cargada que consiste en un núcleo, que está hecho de protones y neutrones, rodeado por electrones. La tabla periódica ordena elementos horizontalmente por el número de protones en el átomo uno debe proporcionar al menos esta energía con el fin de separar la molécula. PS1.B: REACCIONES QUÍMICAS ¿Cómo combinan las sustancias o cambian (reaccionan) para hacer nuevas sustancias? ¿Cómo caracterizan y explican estas reacciones y hacen predicciones sobre ellas? Muchas sustancias reaccionan químicamente con otras sustancias para formar nuevas sustancias con diferentes propiedades. Este cambio en las propiedades resulta de la forma en que los átomos de las sustancias originales se combinan y se reorganizan en las nuevas sustancias. Sin embargo, el número total de cada tipo de átomo se conserva (no cambia) en cualquier proceso químico, y por lo tanto la masa tampoco cambia. La propiedad de la conservación se puede utilizar, junto con el conocimiento de las propiedades químicas de elementos particulares, para describir y predecir los resultados de las reacciones. Los cambios en la materia en los que las moléculas no cambian, pero sus posiciones y su movimiento relativo entre sí también ocurren (por ejemplo, la formación de una solución, la comprensión de las reacciones químicas y las propiedades de los elementos es esencial no sólo para las ciencias físicas, También es un conocimiento fundamental para las ciencias de la vida y las ciencias de la tierra y el espacio Citación sugerida: 5 Dimensión 3: Ideas fundamentales disciplinarias - Ciencias físicas Consejo Nacional de Investigación Un marco para la educación de ciencias de K-12: prácticas, conceptos transversales e ideas básicas Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Un cambio de estado). Estos cambios son generalmente más fáciles de revertir (volver a las condiciones originales) que los cambios químicos. Las reacciones químicas pueden estar ocurriendo dentro de ella que se equilibran dinámicamente con reacciones en direcciones opuestas que proceden a iguales velocidades. Cualquier proceso químico implica un cambio en los enlaces químicos y las energías de enlace relacionadas y por lo tanto en la energía química total de unión. Este cambio se corresponde con una diferencia entre la energía cinética total del conjunto de moléculas reactivas antes de la colisión y la del conjunto de moléculas del producto después de la colisión (conservación de la energía). Algunas reacciones liberan energía (por ejemplo, quemando combustible en presencia de oxígeno), y otras requieren aportación de energía (por ejemplo, síntesis de azúcares a partir de dióxido de carbono y agua). Comprender las reacciones químicas y las propiedades de los elementos es esencial no sólo para las ciencias físicas, sino también es el conocimiento fundamental para las ciencias de la vida y las ciencias de la tierra y el espacio. El ciclo de la materia y las transferencias de energía asociadas en sistemas, de cualquier escala, dependen de procesos físicos y químicos. La reactividad de los iones hidrógeno da lugar a muchos fenómenos biológicos y geofísicos. La capacidad de los átomos de carbono para formar la columna vertebral de estructuras moleculares extendidas es esencial para la química de la vida. El ciclo del carbono implica transferencias entre el carbono en la atmósfera y el carbón en materia viva o materia viviente anterior (incluyendo combustibles fósiles). La proporción de moléculas de oxígeno (es decir, oxígeno en la forma O $ ₂ $) en la atmósfera también cambia en este ciclo. Puntos finales de banda de grado para PS1.B Al final del grado 2. Calentar o enfriar una sustancia puede causar cambios que se pueden observar. A veces, estos cambios son reversibles (por ejemplo, fusión y congelación), ya veces no lo son (por ejemplo, hornear una torta, quemar combustible). Al final del grado 5. Cuando se mezclan dos o más sustancias diferentes, puede formarse una nueva sustancia con propiedades diferentes, dependiendo de las sustancias y de la temperatura. No importa qué reacción o Citación Sugerida: 5 Dimensión 3: Ideas Núcleo Disciplinario - Ciencias Físicas. Consejo nacional de investigación. Un marco para la educación científica de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Cambio de propiedades, el peso total de las sustancias no cambia. (Límite: La masa y el peso no se distinguen en este nivel de grado.) Al final del grado 8. Las sustancias reaccionan químicamente de manera característica. En un proceso químico, los átomos que componen las sustancias originales se reagrupan en diferentes moléculas, y estas nuevas sustancias tienen propiedades diferentes de las de los reactivos. El número total de cada tipo de átomo se conserva, y por lo tanto la masa no cambia. Algunas reacciones químicas liberan energía, otras almacenan energía. Al final del grado 12. Los procesos químicos, sus velocidades y si la energía es almacenada o liberada pueden entenderse en términos de colisiones de moléculas y de reordenamientos de átomos en nuevas moléculas, con los consiguientes cambios en la energía de unión total La suma de todas las energías de enlace en el conjunto de moléculas) que se corresponden con los cambios en la energía cinética. En muchas situaciones, un equilibrio dinámico y dependiente de la condición entre una reacción y la reacción inversa determina el número de todos los tipos de moléculas presentes. El hecho de que los átomos se conserven, junto con el conocimiento de las propiedades químicas de los elementos involucrados, se puede utilizar para describir y predecir las reacciones químicas. Los procesos químicos y las propiedades de los materiales subyacen a muchos fenómenos biológicos y geofísicos importantes. PS1.C: PROCESOS NUCLEARES Qué fuerzas mantienen los núcleos unidos y median los procesos nucleares Son importantes los fenómenos que involucran núcleos, ya que explican la formación y abundancia de los elementos, la radiactividad, la liberación de energía del sol y otras estrellas y la generación De la energía nuclear. Para explicar y predecir los procesos nucleares, dos tipos adicionales de interacciones deben ser introducidos. Ellos juegan un papel fundamental en los núcleos, aunque no a mayor escala porque sus efectos son de rango muy corto. La interacción nuclear fuerte proporciona la fuerza primaria que mantiene los núcleos juntos y determina las energías de unión nuclear. Sin ella, las fuerzas electromagnéticas entre los protones harían que todos los núcleos distintos del hidrógeno fueran inestables. Los procesos nucleares mediados por estas interacciones incluyen la fusión, la fisión y el decaimiento radiactivo de los núcleos inestables. Estos procesos implican cambios en el núcleo Cita Sugerida: 5 Dimensión 3: Ideas Núcleo Disciplinario - Ciencias Físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. (Como se describe por E mc 2), y típicamente liberan mucha más energía por átomo involucrado que los procesos químicos. La fusión nuclear es un proceso en el que una colisión de dos pequeños núcleos eventualmente resulta en la formación de un solo núcleo más masivo con mayor energía de unión neta y por lo tanto una liberación de energía. Se produce sólo en condiciones de temperatura y presión extremadamente altas. La fusión nuclear que ocurre en los núcleos de las estrellas proporciona la energía liberada (como luz) de esas estrellas. El Big Bang produjo materia en forma de hidrógeno y pequeñas cantidades de helio y litio. Con el tiempo, las estrellas (incluyendo explosiones de supernovas) han producido y dispersado todos los átomos más masivos, partiendo de elementos primordiales de baja masa, principalmente hidrógeno. La fisión nuclear es un proceso en el cual un núcleo masivo se divide en dos o más núcleos más pequeños, que se separan a gran energía. Los núcleos producidos a menudo no son estables y sufren posteriores decaimientos radiactivos. Un fragmento de fisión común es una partícula alfa, que es simplemente otro nombre para un núcleo de helio, dado antes de que se identificara este tipo de. Además de las partículas alfa, otros tipos de decaimientos radiactivos producen otras formas de radiación, originalmente etiquetadas como partículas y ahora reconocidas como electrones o positrones, y fotones (es decir, radiación electromagnética de alta frecuencia), respectivamente. Debido a la liberación de alta energía en las transiciones nucleares, la radiación emitida (ya sea de tipo alfa, beta o gamma) puede ionizar átomos y puede causar daños al tejido biológico. La fisión nuclear y los decaimientos radiactivos limitan el conjunto de isótopos estables de los elementos y el tamaño del mayor núcleo estable. Los decaimientos radiactivos espontáneos siguen una ley de decaimiento exponencial característica, con una vida útil específica (escala de tiempo) para cada uno de tales procesos, las vidas de diferentes procesos de desintegración nuclear van desde fracciones de un segundo hasta miles de años. Algunos isótopos inestables pero de larga vida están presentes en rocas y minerales. El conocimiento de sus vidas nucleares permite la datación radiométrica que se utiliza para determinar las edades de las rocas y otros materiales de las proporciones de isótopos presentes. En los procesos de fisión, fusión y desintegración beta, los átomos cambian de tipo, pero el número total de protones más neutrones se conserva. Los procesos beta implican un tipo adicional de interacción (la interacción débil) que puede cambiar los neutrones en protones o viceversa, junto con la emisión o absorción de electrones o positrones y de neutrinos. Los neutrones aislados se descomponen por este proceso. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Puntos finales de la banda de grado para PS1.C Al final del grado 2. Intencionalmente dejados en blanco. Al final del grado 5. Intencionalmente en blanco. Al final del grado 8. La fusión nuclear puede resultar en la fusión de dos núcleos para formar uno más grande, junto con la liberación de energía significativamente más por átomo que cualquier proceso químico. Se produce sólo en condiciones de temperatura y presión extremadamente altas. La fusión nuclear que ocurre en los núcleos de las estrellas proporciona la energía liberada (como luz) de esas estrellas y produjo todos los átomos más masivos del hidrógeno primordial. Así, los elementos encontrados en la Tierra y en todo el universo (aparte del hidrógeno y la mayor parte del helio, que son primordiales) se formaron en las estrellas o supernovas mediante procesos de fusión. Al final del grado 12. Los procesos nucleares, incluyendo fusión, fisión y desintegración radiactiva de núcleos inestables, implican cambios en las energías de unión nuclear. El número total de neutrones más protones no cambia en ningún proceso nuclear. Las interacciones nucleares fuertes y débiles determinan la estabilidad y los procesos nucleares. Los decaimientos radiactivos espontáneos siguen una ley de decaimiento exponencial característica. Las vidas nucleares permiten que la datación radiométrica se utilice para determinar las edades de las rocas y otros materiales de las relaciones isotópicas presentes. Las estrellas normales dejan de producir luz después de haber convertido todo el material en sus núcleos en carbono o, para estrellas más masivas, planchar. Elementos más masivos que el hierro están formados por procesos de fusión, pero sólo en las condiciones extremas de las explosiones de supernovas, lo que explica por qué son relativamente raros. Movimiento y Estabilidad: Fuerzas e Interacciones Cómo se puede explicar y predecir las interacciones entre los objetos y dentro de los sistemas de objetos Interacciones entre dos objetos cualquiera puede causar cambios en uno o ambos. Una comprensión de las fuerzas entre los objetos es importante para describir cómo cambian sus movimientos, así como para predecir la estabilidad o la inestabilidad en los sistemas a cualquier escala. Todas las fuerzas entre los objetos surgen de unos pocos tipos de interacciones: la gravedad, el electromagnetismo y las fuertes y débiles interacciones nucleares. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. PS2.A: FORZOS Y MOVIMIENTO ¿Cómo se puede predecir el movimiento continuo de un objeto, los cambios de movimiento o la estabilidad? Las interacciones de un objeto con otro objeto pueden explicarse y predecir utilizando el concepto de fuerzas que pueden causar un cambio en el movimiento de uno O ambos de los objetos que interactúan. Una fuerza individual actúa sobre un objeto particular y es descrita por su fuerza y dirección. Se pueden medir las fuerzas de las fuerzas y comparar sus valores. Lo que sucede cuando una fuerza se aplica a un objeto depende no sólo de esa fuerza sino también de todas las demás fuerzas que actúan sobre ese objeto. Un objeto estático tiene típicamente múltiples fuerzas que actúan en él, pero suman a cero. Sin embargo, si la fuerza total (suma vectorial) sobre un objeto no es cero, su movimiento cambiará. A veces las fuerzas sobre un objeto también pueden cambiar su forma u orientación. Para cualquier par de objetos que interactúan, la fuerza ejercida por el primer objeto sobre el segundo objeto es igual en fuerza a la fuerza que el segundo objeto ejerce en la primera pero en la dirección opuesta (tercera ley de Newton). En la macroescala, el movimiento de un objeto sometido a fuerzas está gobernado por la segunda ley de Newton del movimiento. Bajo circunstancias cotidianas, la expresión matemática de esta ley en la forma F ma (total de la fuerza de la masa de aceleración) predice con precisión los cambios en el movimiento de un solo objeto macroscópico de una masa dada debido a la fuerza total sobre ella. Pero a velocidades cercanas a la velocidad de la luz, la segunda ley no es aplicable sin modificaciones. Tampoco se aplica a los objetos en las escalas molecular, atómica y subatómica, oa un objeto cuya masa está cambiando al mismo tiempo que su velocidad. Una comprensión de las fuerzas entre los objetos es importante para describir cómo cambian sus movimientos, así como para predecir la estabilidad o la inestabilidad en los sistemas a cualquier escala. Citación sugerida: 5 Dimensión 3: Ideas básicas disciplinarias - Ciencias físicas. Consejo nacional de investigación. Un marco para la educación de las ciencias de K-12: Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Para velocidades que son pequeñas en comparación con la velocidad de la luz, el momento de un objeto se define como su masa veces su velocidad. Para cualquier sistema de objetos que interactúan, el momentum total dentro del sistema cambia solamente debido a la transferencia del momentum dentro o fuera del sistema, debido a las fuerzas externas que actúan en el sistema oa los flujos de la materia. Dentro de un sistema aislado de objetos que interactúan, cualquier cambio en el momento de un objeto es equilibrado por un cambio igual y opuesto en el momento total de los otros objetos. Así, el momentum total es una cantidad conservada. Puntos finales de la banda de grado para PS2.A Al final del grado 2. Los objetos se tiran o empujan entre sí cuando chocan o están conectados. Los empujones y los tirones pueden tener diferentes fuerzas y direcciones. Empujar o tirar de un objeto puede cambiar la velocidad o dirección de su movimiento y puede iniciarlo o detenerlo. Un objeto que se desliza sobre una superficie o que se sienta en una pendiente experimenta un tirón debido a la fricción en el objeto debido a la superficie que se opone al movimiento del objeto. Al final del grado 5. Cada fuerza actúa sobre un objeto particular y tiene una fuerza y una dirección. Un objeto en reposo normalmente tiene múltiples fuerzas que actúan sobre él, pero se suman para dar cero fuerza neta sobre el objeto. Las fuerzas que no suman a cero pueden causar cambios en el objeto cuando el movimiento pasado presenta un patrón regular, el movimiento futuro puede predecirse a partir de él. (Límite: No se introducen términos técnicos, tales como magnitud, velocidad, cantidad de movimiento y cantidad vectorial, pero el concepto de que algunas cantidades necesitan tanto tamaño como dirección se desarrolla.) Al final del grado 8. Para cualquier par de objetos que interactúan, la fuerza ejercida por el primer objeto en el segundo objeto es igual en fuerza a la fuerza que el segundo objeto ejerce sobre la primera pero en la dirección opuesta (Newton si la fuerza total sobre el objeto no es cero , Su movimiento cambiará. Cuanto mayor sea la masa del objeto, mayor será la fuerza necesaria para lograr el mismo cambio de movimiento. Para cualquier objeto dado, una fuerza más grande provoca un cambio de movimiento más grande. Las fuerzas sobre un objeto también pueden cambiar su movimiento Forma o orientación Todas las posiciones de los objetos y las direcciones de las fuerzas y los movimientos deben ser descritos en un marco de referencia elegido arbitrariamente Cita Sugerida: 5 Dimensión 3: Ideas Núcleo Disciplinario - Ciencias Físicas Consejo Nacional de Investigación. : Prácticas, conceptos transversales e ideas básicas. Washington, DC: La Academia Nacional de Prensa, 2012. doi: 10.17226 / 13165. Y unidades de tamaño arbitrariamente elegidas. Para compartir información con otras personas, estas opciones también deben ser compartidas. Al final del grado 12. La segunda ley de Newton predice con precisión los cambios en el movimiento de los objetos macroscópicos, pero requiere revisión para las escalas subatómicas o para velocidades cercanas a la velocidad de la luz. (Límite: No se incluyen detalles de la física cuántica o de la relatividad en este nivel de grado.) Momentum se define para un marco de referencia particular, es la masa multiplicada por la velocidad del objeto. En cualquier sistema, el momento total siempre se conserva. Si un sistema interactúa con objetos fuera de sí, el impulso total del sistema puede cambiar sin embargo, cualquier cambio de este tipo es equilibrado por cambios en el momento de los objetos fuera del sistema. PS2.B: TIPOS DE INTERACCIONES Qué fuerzas subyacentes explican la variedad de interacciones observadas Todas las fuerzas entre objetos surgen de unos pocos tipos de interacciones: la gravedad, el electromagnetismo y las interacciones nucleares fuertes y débiles. Las colisiones entre objetos implican fuerzas entre ellos que pueden cambiar su movimiento. Cualquier dos objetos en contacto también ejercen fuerzas entre sí que son de origen electromagnético. Estas fuerzas resultan de deformaciones de las subestructuras de objetos y de las cargas eléctricas de las partículas que forman esas subestructuras (por ejemplo, una mesa que soporta un libro, fuerzas de fricción). Las fuerzas gravitacionales, eléctricas y magnéticas entre un par de objetos no requieren que estén en contacto. Estas fuerzas se explican por campos de fuerza que contienen energía y pueden transferir energía a través del espacio. Estos campos pueden ser mapeados por su efecto en un objeto de prueba (masa, carga o imán, respectivamente). Los objetos con masa son fuentes de campos gravitatorios y son afectados por los campos gravitacionales de todos los otros objetos con masa. Las fuerzas gravitacionales son siempre atractivas. Para dos objetos de escala humana, estas fuerzas son demasiado pequeñas para observar sin instrumentación sensible. Las interacciones gravitatorias son no despreciables, sin embargo, cuando están involucrados objetos muy masivos. Thus the gravitational force due to Earth, acting on an object near Earth s law of universal gravitation provides the mathematical model to describe and predict the effects of gravitational forces between distant objects. These long-range gravitational interactions govern the evolution and Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. maintenance of large-scale structures in the universe (e. g. the solar system, galaxies) and the patterns of motion within them. Electric forces and magnetic forces are different aspects of a single electromagnetic interaction. Such forces can be attractive or repulsive, depending on the relative sign of the electric charges involved, the direction of current flow, and the orientation of magnets. The forces s law provides the mathematical model to describe and predict the effects of electrostatic forces (relating to stationary electric charges or fields) between distant objects. The strong and weak nuclear interactions are important inside atomic nuclei. These short-range interactions determine nuclear sizes, stability, and rates of radioactive decay (see PS1.C ). Grade Band Endpoints for PS2.B By the end of grade 2. When objects touch or collide, they push on one another and can change motion or shape. By the end of grade 5. Objects in contact exert forces on each other (friction, elastic pushes and pulls). Electric, magnetic, and gravitational forces between a pair of objects do not require that the objects be in contact s center. By the end of grade 8. Electric and magnetic (electromagnetic) forces can be attractive or repulsive, and their sizes depend on the magnitudes of the charges, currents, or magnetic strengths involved and on the Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. distances between the interacting objects. Gravitational forces are always attractive. There is a gravitational force between any two masses, but it is very small except when one or both of the objects have large mass for example, Earth and the sun. Long-range gravitational interactions govern the evolution and maintenance of large-scale systems in space, such as galaxies or the solar system, and determine the patterns of motion within those structures. Forces that act at a distance (gravitational, electric, and magnetic) can be explained by force fields that extend through space and can be mapped by their effect on a test object (a ball, a charged object, or a magnet, respectively). By the end of grade 12. Newton s law provide the mathematical models to describe and predict the effects of gravitational and electrostatic forces between distant objects. Forces at a distance are explained by fields permeating space that can transfer energy through space. Magnets or changing electric fields cause magnetic fields electric charges or changing magnetic fields cause electric fields. Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects. The strong and weak nuclear interactions are important inside atomic nuclei for example, they determine the patterns of which nuclear isotopes are stable and what kind of decays occur for unstable ones. PS2.C: STABILITY AND INSTABILITY IN PHYSICAL SYSTEMS Why are some physical systems more stable than others Events and processes in a system typically involve multiple interactions occurring simultaneously or in sequence. The system s stability or instability and its rate of evolution depend on the balance or imbalance among these multiple effects. A stable system is one in which the internal and external forces are such that any small change results in forces that return the system to its prior state (e. g. a weight hanging from a string). A system can be static but unstable, with any small change leading to forces that tend to increase that change (e. g. a ball at the top of a hill). A system can be changing but have a stable repeating cycle of changes, with regular patterns of change that allow predictions about the system s future (e. g. Earth orbiting the sun). And a stable system can appear to be unchanging when flows or processes within it are going on at opposite but equal rates (e. g. water in a dam at a constant height but with water flowing in that offsets the Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. water flowing out a person maintaining steady weight but eating food, burning calories, and excreting waste). Stability and instability in any system depend on the balance of competing effects. A steady state of a complex system can be maintained through a set of feedback mechanisms, but changes in conditions can move the system out of its range of stability (e. g. homeostasis breaks down at too high or too low a temperature). With no energy inputs, a system starting out in an unstable state will continue to change until it reaches a stable configuration (e. g. the temperatures of hot and cold objects in contact). Viewed at a given scale, stable systems may appear static or dynamic. Conditions and properties of the objects within a system affect the rates of energy transfer and thus how fast or slowly a process occurs (e. g. heat conduction, the diffusion of particles in a fluid). When a system has a great number of component pieces, one may not be able to predict much about its precise future. For such systems (e. g. with very many colliding molecules), one can often predict average but not detailed properties and behaviors (e. g. average temperature, motion, and rates of chemical change but not the trajectories of particular molecules). Grade Band Endpoints for PS2.C By the end of grade 2. Whether an object stays still or moves often depends on the effects of multiple pushes and pulls on it (e. g. multiple players trying to pull an object in different directions). It is useful to investigate what pushes and pulls keep something in place (e. g. a ball on a slope, a ladder leaning on a wall) as well as what makes something change or move. By the end of grade 5. A system can change as it moves in one direction (e. g. a ball rolling down a hill), shifts back and forth (e. g. a swinging pendulum), or goes through cyclical patterns (e. g. day and night). Examining how the forces on and within the system change as it moves can help to explain the system s patterns of change. A system can appear to be unchanging when processes within the system are occurring at opposite but equal rates (e. g. water behind a dam is at a constant height because water is flowing in at the same rate that water is flowing out). Changes can happen very quickly or very slowly and are sometimes hard to see (e. g. plant growth). Conditions and properties of the objects within a system affect how fast or slowly a process occurs (e. g. heat conduction rates). Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. By the end of grade 8. A stable system is one in which any small change results in forces that return the system to its prior state (e. g. a weight hanging from a string). A system can be static but unstable (e. g. a pencil standing on end). A system can be changing but have a stable repeating cycle of changes such observed regular patterns allow predictions about the system s future (e. g. Earth orbiting the sun). Many systems, both natural and engineered, rely on feedback mechanisms to maintain stability, but they can function only within a limited range of conditions. With no energy inputs, a system starting out in an unstable state will continue to change until it reaches a stable configuration (e. g. sand in an hourglass). By the end of grade 12 . Systems often change in predictable ways understanding the forces that drive the transformations and cycles within a system, as well as the forces imposed on the system from the outside, helps predict its behavior under a variety of conditions. When a system has a great number of component pieces, one may not be able to predict much about its precise future. For such systems (e. g. with very many colliding molecules), one can often predict average but not detailed properties and behaviors (e. g. average temperature, motion, and rates of chemical change but not the trajectories or other changes of particular molecules). Systems may evolve in unpredictable ways when the outcome depends sensitively on the starting condition and the starting condition cannot be specified precisely enough to distinguish between different possible outcomes. How is energy transferred and conserved Interactions of objects can be explained and predicted using the concept of transfer of energy from one object or system of objects to another. The total energy within a defined system changes only by the transfer of energy into or out of the system. PS3.A: DEFINITIONS OF ENERGY That there is a single quantity called energy is due to the remarkable fact that a system s total energy is conserved. Regardless of the quantities of energy transferred Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. between subsystems and stored in various ways within the system, the total energy of a system changes only by the amount of energy transferred into and out of the system. At the macroscopic scale, energy manifests itself in multiple phenomena, such as motion, light, sound, electrical and magnetic fields, and thermal energy. Historically, different units were introduced for the energy present in these different phenomena, and it took some time before the relationships among them were recognized. Energy is best understood at the microscopic scale, at which it can be modeled as either motions of particles or as stored in force fields (electric, magnetic, gravitational) that mediate interactions between particles. This last concept includes electromagnetic radiation, a phenomenon in which energy stored in fields moves across space (light, radio waves) with no supporting matter medium. Motion energy is also called kinetic energy defined in a given reference frame, it is proportional to the mass of the moving object and grows with the square of its speed. Matter at any temperature above absolute zero contains thermal energy. Thermal energy is the random motion of particles (whether vibrations in solid matter or molecules or free motion in a gas), this energy is distributed among all the particles in a system through collisions and interactions at a distance. In contrast, a sound wave is a moving pattern of particle vibrations that transmits energy through a medium. Electric and magnetic fields also contain energy any change in the relative positions of charged objects (or in the positions or orientations of magnets) changes the fields between them and thus the amount of energy stored in those fields. When a particle in a molecule of solid matter vibrates, energy is continually being transformed back and forth between the energy of motion and the energy stored in the electric and magnetic fields within the matter. Matter in a stable form minimizes the stored energy in the electric and magnetic fields within it this defines the equilibrium positions and spacing of the atomic nuclei in a molecule or an extended solid and the form of their combined electron charge distributions (e. g. chemical bonds, metals). Energy stored in fields within a system can also be described as potential energy. For any system where the stored energy depends only on the spatial configuration of the system and not on its history, potential energy is a useful concept (e. g. a massive object above Earth s surface, a compressed or stretched spring). It is defined as a difference in energy compared to some arbitrary reference configuration of a system. For example, lifting an object increases the stored energy in the gravitational field between that object and Earth (gravitational potential energy) Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. compared to that for the object at Earth s kinetic energy increases. When a pendulum swings, some stored energy is transformed into kinetic energy and back again into stored energy during each swing. (In both examples energy is transferred out of the system due to collisions with air and for the pendulum also by friction in its support.) Any change in potential energy is accompanied by changes in other forms of energy within the system, or by energy transfers into or out of the system. Electromagnetic radiation (such as light and X-rays) can be modeled as a wave of changing electric and magnetic fields. At the subatomic scale (i. e. in quantum theory), many phenomena involving electromagnetic radiation (e. g. photoelectric effect) are best modeled as a stream of particles called photons. Electromagnetic radiation from the sun is a major source of energy for life on Earth. The idea that there are different forms of energy, such as thermal energy, mechanical energy, and chemical energy, is misleading, as it implies that the nature of the energy in each of these manifestations is distinct when in fact they all are ultimately, at the atomic scale, some mixture of kinetic energy, stored energy, and radiation. It is likewise misleading to call sound or light a form of energy they are phenomena that, among their other properties, transfer energy from place to place and between objects. Grade Band Endpoints for PS3.A By the end of grade 2. Intentionally left blank. By the end of grade 5. The faster a given object is moving, the more energy it possesses. Energy can be moved from place to place by moving objects or through sound, light, or electric currents. (Boundary: At this grade level, no attempt is made to give a precise or complete definition of energy.) Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. At the macroscopic scale, energy manifests itself in multiple phenomena, such as motion, light, sound, electrical and magnetic fields, and thermal energy. By the end of grade 8. Motion energy is properly called kinetic energy it is proportional to the mass of the moving object and grows with the square of its speed. A system of objects may also contain stored (potential) energy, depending on their relative positions. For example, energy is stored when an object is raised, and energy is released when the object falls or is lowered. Energy is also stored in the electric fields between charged particles and the magnetic fields between magnets, and it changes when these objects are moved relative to one another. Stored energy is decreased in some chemical reactions and increased in others. The term it refers to energy transferred when two objects or systems are at different temperatures. Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present. By the end of grade 12. Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system may mean energy stored in a battery or energy transmitted by electric currents. Historically, different units and names were used for the energy present in these different phenomena, and it took some time before the relationships between them were recognized. These relationships are better understood at Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. the microscopic scale, at which all of the different manifestations of energy can be modeled as either motions of particles or energy stored in fields (which mediate interactions between particles). This last concept includes radiation, a phenomenon in which energy stored in fields moves across space. PS3.B: CONSERVATION OF ENERGY AND ENERGY TRANSFER What is meant by conservation of energy How is energy transferred between objects or systems The total change of energy in any system is always equal to the total energy transferred into or out of the system. This is called conservation of energy. Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems. Many different types of phenomena can be explained in terms of energy transfers. Mathematical expressions, which quantify changes in the forms of energy within a system and transfers of energy into or out of the system, allow the concept of conservation of energy to be used to predict and describe the behavior of a system. When objects collide or otherwise come in contact, the motion energy of one object can be transferred to change the motion or stored energy (e. g. change in shape or temperature) of the other objects. For macroscopic objects, any such process (e. g. collisions, sliding contact) also transfers some of the energy to the surrounding air by sound or heat. For molecules, collisions can also result in energy transfers through chemical processes, which increase or decrease the total amount of stored energy within a system of atoms the change in stored energy is always balanced by a change in total kinetic energy that of the molecules present after the process compared with the kinetic energy of the molecules present before it. Energy can also be transferred from place to place by electric currents. Heating is another process for transferring energy. Heat transfer occurs when two objects or systems are at different temperatures. Energy moves out of higher temperature objects and into lower temperature ones, cooling the former and heating the latter. This transfer happens in three different ways by conduction within solids, by the flow of liquid or gas (convection), and by radiation, which can travel across space. Even when a system is isolated (such as Earth in space), energy is continually being transferred into and out of it by radiation. The processes underlying convection and conduction can be understood in terms of models of the possible motions of particles in matter. Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. Radiation can be emitted or absorbed by matter. When matter absorbs light or infrared radiation, the energy of that radiation is transformed to thermal motion of particles in the matter, or, for shorter wavelengths (ultraviolet, X-ray), the radiation s energy is absorbed within the atoms or molecules and may possibly ionize them by knocking out an electron. Uncontrolled systems always evolve toward more stable states that is, toward more uniform energy distribution within the system or between the system and its environment (e. g. water flows downhill, objects that are hotter than their surrounding environment cool down). Any object or system that can degrade with no added energy is unstable. Eventually it will change or fall apart, although in some cases it may remain in the unstable state for a long time before decaying (e. g. long-lived radioactive isotopes). Grade-Level Endpoints for PS3.B By the end of grade 2. Sunlight warms Earth s surface. By the end of grade 5. Energy is present whenever there are moving objects, sound, light, or heat. When objects collide, energy can be transferred from one object to another, thereby changing their motion. In such collisions, some energy is typically also transferred to the surrounding air as a result, the air gets heated and sound is produced. Light also transfers energy from place to place. For example, energy radiated from the sun is transferred to Earth by light. When this light is absorbed, it warms Earth s land, air, and water and facilitates plant growth. Energy can also be transferred from place to place by electric currents, which can then be used locally to produce motion, sound, heat, or light. The currents may have been produced to begin with by transforming the energy of motion into electrical energy (e. g. moving water driving a spinning turbine which generates electric currents). By the end of grade 8 . When the motion energy of an object changes, there is inevitably some other change in energy at the same time. For example, the friction that causes a moving object to stop also results in an increase in the thermal energy in both surfaces eventually heat energy is transferred to the surrounding environment as the surfaces cool. Similarly, to make an object start moving or to keep it moving when friction forces transfer energy away from it, Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. energy must be provided from, say, chemical (e. g. burning fuel) or electrical (e. g. an electric motor and a battery) processes. The amount of energy transfer needed to change the temperature of a matter sample by a given amount depends on the nature of the matter, the size of the sample, and the environment. Energy is transferred out of hotter regions or objects and into colder ones by the processes of conduction, convection, and radiation. By the end of grade 12. Conservation of energy means that the total change of energy in any system is always equal to the total energy transferred into or out of the system. Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems. Mathematical expressions, which quantify how the stored energy in a system depends on its configuration (e. g. relative positions of charged particles, compression of a spring) and how kinetic energy depends on mass and speed, allow the concept of conservation of energy to be used to predict and describe system behavior. The availability of energy limits what can occur in any system. Uncontrolled systems always evolve toward more stable states that is, toward more uniform energy distribution (e. g. water flows downhill, objects hotter than their surrounding environment cool down). Any object or system that can degrade with no added energy is unstable. Eventually it will do so, but if the energy releases throughout the transition are small, the process duration can be very long (e. g. long-lived radioactive isotopes). PS3.C RELATIONSHIP BETWEEN ENERGY AND FORCES How are forces related to energy When two objects interact, each one exerts a force on the other. These forces can transfer energy between the objects. Forces between two objects at a distance are explained by force fields (gravitational, electric, or magnetic) between them. Contact forces between colliding objects can be modeled at the microscopic level as due to electromagnetic force fields between the surface particles. When two objects interacting via a force field change their relative position, the energy in the Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. force field between them changes. For any such pair of objects the force on each object acts in the direction such that motion of that object in that direction would reduce the energy in the force field between the two objects. However, prior motion and other forces also affect the actual direction of motion. Patterns of motion, such as a weight bobbing on a spring or a swinging pendulum, can be understood in terms of forces at each instant or in terms of transformation of energy between the motion and one or more forms of stored energy. Elastic collisions between two objects can be modeled at the macroscopic scale using conservation of energy without having to examine the detailed microscopic forces. Grade Band Endpoints for PS3.C By the end of grade 2. A bigger push or pull makes things go faster. Faster speeds during a collision can cause a bigger change in shape of the colliding objects. By the end of grade 5 . When objects collide, the contact forces transfer energy so as to change the objects motions. Magnets can exert forces on other magnets or on magnetizable materials, causing energy transfer between them (e. g. leading to changes in motion) even when the objects are not touching. By the end of grade 8. When two objects interact, each one exerts a force on the other that can cause energy to be transferred to or from the object. For example, when energy is transferred to an Earth-object system as an object is raised, the gravitational field energy of the system increases. This energy is released as the object falls the mechanism of this release is the gravitational force. Likewise, two magnetic and electrically charged objects interacting at a distance exert forces on each other that can transfer energy between the interacting objects. By the end of grade 12 . Force fields (gravitational, electric, and magnetic) contain energy and can transmit energy across space from one object to another. When two objects interacting through a force field change relative position, the energy stored in the force field is changed. Each force between the two interacting objects acts in the direction such that motion in that direction would reduce the energy in the force field between the objects. However, prior motion and other forces also affect the actual direction of motion. Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. PS3.D: ENERGY IN CHEMICAL PROCESSES AND EVERYDAY LIFE How do food and fuel provide energy If energy is conserved, why do people say it is produced or used In ordinary language, people speak of in the same sense that paper is not destroyed when it is written on, it still exists but is not readily available for further use. Naturally occurring food and fuel contain complex carbon-based molecules, chiefly derived from plant matter that has been formed by photosynthesis. The chemical reaction of these molecules with oxygen releases energy such reactions provide energy for most animal life and for residential, commercial, and industrial activities. Electric power generation is based on fossil fuels (i. e. coal, oil, and natural gas), nuclear fission, or renewable resources (e. g. solar, wind, tidal, geothermal, and hydro power). Transportation today chiefly depends on fossil fuels, but the use of electric and alternative fuel (e. g. hydrogen, biofuel) vehicles is increasing. All forms of electricity generation and transportation fuels have associated economic, social, and environmental costs and benefits, both short and long term. Technological advances and regulatory decisions can change the balance of those costs and benefits. Although energy cannot be destroyed, it can be converted to less useful forms. In designing a system for energy storage, for energy distribution, or to perform some practical task (e. g. to power an airplane), it is important to design for maximum efficiency thereby ensuring that the largest possible fraction of the energy is used for the desired purpose rather than being transferred out of the Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. system in unwanted ways (e. g. through friction, which eventually results in heat energy transfer to the surrounding environment). Improving efficiency reduces costs, waste materials, and many unintended environmental impacts. Grade Band Endpoints for PS3.D By the end of grade 2 . When two objects rub against each other, this interaction is called friction. Friction between two surfaces can warm of both of them (e. g. rubbing hands together). There are ways to reduce the friction between two objects. By the end of grade 5 . The expression energy (e. g. to move around), most often the energy is transferred to heat the surrounding environment. The energy released by burning fuel or digesting food was once energy from the sun that was captured by plants in the chemical process that forms plant matter (from air and water). (Boundary: The fact that plants capture energy from sunlight is introduced at this grade level, but details of photosynthesis are not.) It is important to be able to concentrate energy so that it is available for use where and when it is needed. For example, batteries are physically transportable energy storage devices, whereas electricity generated by power plants is transferred from place to place through distribution systems. By the end of grade 8 . The chemical reaction by which plants produce complex food molecules (sugars) requires an energy input (i. e. from sunlight) to occur. In this reaction, carbon dioxide and water combine to form carbon-based organic molecules and release oxygen. (Boundary: Further details of the photosynthesis process are not taught at this grade level.) Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. Both the burning of fuel and cellular digestion in plants and animals involve chemical reactions with oxygen that release stored energy. In these processes, complex molecules containing carbon react with oxygen to produce carbon dioxide and other materials. Machines can be made more efficient, that is, require less fuel input to perform a given task, by reducing friction between their moving parts and through aerodynamic design. Friction increases energy transfer to the surrounding environment by heating the affected materials. By the end of grade 12. Nuclear fusion processes in the center of the sun release the energy that ultimately reaches Earth as radiation. The main way in which that solar energy is captured and stored on Earth is through the complex chemical process known as photosynthesis. Solar cells are human-made devices that likewise capture the sun s energy and produce electrical energy. A variety of multistage physical and chemical processes in living organisms, particularly within their cells, account for the transport and transfer (release or uptake) of energy needed for life functions. All forms of electricity generation and transportation fuels have associated economic, social, and environmental costs and benefits, both short and long term. Although energy cannot be destroyed, it can be converted to less useful forms for example, to thermal energy in the surrounding environment. Machines are judged as efficient or inefficient based on the amount of energy input needed to perform a particular useful task. Inefficient machines are those that produce more waste heat while performing a task and thus require more energy input. It is therefore important to design for high efficiency so as to reduce costs, waste materials, and many environmental impacts. Waves and Their Applications in Technologies for Information Transfer How are waves used to transfer energy and information Waves are a repeating pattern of motion that transfers energy from place to place without overall displacement of matter. Light and sound are wavelike phenomena. By understanding wave properties and the interactions of electromagnetic radiation with matter, scientists and engineers can design systems for transferring information across long distances, storing information, and investigating nature on many scales some of them far beyond direct human perception. Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. corresponding to each color. When a wave meets the surface between two different materials or conditions (e. g. air to water), part of the wave is reflected at that surface and another part continues on, but at a different speed. The change of speed of the wave when passing from one medium to another can cause the wave to change direction or refract. These wave properties are used in many applications (e. g. lenses, seismic probing of Earth). Grade Band Endpoints for PS4.A By the end of grade 2. Waves, which are regular patterns of motion, can be made in water by disturbing the surface. When waves move across the surface of deep water, the water goes up and down in place it does not move in the direction of the wave except when the water meets the beach. Sound can make matter vibrate, and vibrating matter can make sound. By the end of grade 5. Waves of the same type can differ in amplitude (height of the wave) and wavelength (spacing between wave peaks). Waves can add or cancel one another as they cross, depending on their relative phase (i. e. relative position of peaks and troughs of the waves), but they emerge unaffected by each other. (Boundary: The discussion at this grade level is qualitative only it can be based on the fact that two different sounds can pass a location in different directions without getting mixed up.) Earthquakes cause seismic waves, which are waves of motion in Earth s crust. By the end of grade 8. A simple wave has a repeating pattern with a specific wavelength, frequency, and amplitude. A sound wave needs a medium through which it is transmitted. Geologists use seismic waves and their reflection at interfaces between layers to probe structures deep in the planet. By the end of grade 12 . The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing. The reflection, refraction, and transmission of waves at an interface between two media can be modeled on the basis of these properties. Combining waves of different frequencies can make a wide variety of patterns and thereby encode and transmit information. Information can be digitized Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. (e. g. a picture stored as the values of an array of pixels) in this form, it can be stored reliably in computer memory and sent over long distances as a series of wave pulses. Resonance is a phenomenon in which waves add up in phase in a structure, growing in amplitude due to energy input near the natural vibration frequency. Structures have particular frequencies at which they resonate. This phenomenon (e. g. waves in a stretched string, vibrating air in a pipe) is used in speech and in the design of all musical instruments. PS4.B: ELECTROMAGNETIC RADIATION What is light How can one explain the varied effects that involve light What other forms of electromagnetic radiation are there Electromagnetic radiation (e. g. radio, microwaves, light) can be modeled as a wave pattern of changing electric and magnetic fields or, alternatively, as particles. Each model is useful for understanding aspects of the phenomenon and its inter-actions with matter, and quantum theory relates the two models. Electromagnetic By understanding wave properties and the interactions of electromagnetic radiation with matter, scientists and engineers can design systems for transferring information across long distances, storing information, and investigating nature on many scales some of them far beyond direct human perception. Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. waves can be detected over a wide range of frequencies, of which the visible spectrum of colors detectable by human eyes is just a small part. Many modern technologies are based on the manipulation of electromagnetic waves. All electromagnetic radiation travels through a vacuum at the same speed, called the speed of light. Its speed in any given medium depends on its wavelength and the properties of that medium. At the surface between two media, like any wave, light can be reflected, refracted (its path bent), or absorbed. What occurs depends on properties of the surface and the wavelength of the light. When shorter wavelength electromagnetic radiation (ultraviolet, X-rays, gamma rays) is absorbed in matter, it can ionize atoms and cause damage to living cells. However, because X-rays can travel through soft body matter for some distance but are more rapidly absorbed by denser matter, particularly bone, they are useful for medical imaging. Photovoltaic materials emit electrons when they absorb light of a high-enough frequency. This phenomenon is used in barcode scanners and systems, as well as in solar cells. It is best explained using a particle model of light. Any object emits a spectrum of electromagnetic radiation that depends on its temperature. In addition, atoms of each element emit and preferentially absorb characteristic frequencies of light. These spectral lines allow identification of the presence of the element, even in microscopic quantities or for remote objects, such as a star. Nuclear transitions that emit or absorb gamma radiation also have distinctive gamma ray wavelengths, a phenomenon that can be used to identify and trace specific radioactive isotopes. Grade Band Endpoints for PS4.B By the end of grade 2. Objects can be seen only when light is available to illuminate them. Very hot objects give off light (e. g. a fire, the sun). Some materials allow light to pass through them, others allow only some light through, and others block all the light and create a dark shadow on any Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. surface beyond them (i. e. on the other side from the light source), where the light cannot reach. Mirrors and prisms can be used to redirect a light beam. (Boundary: The idea that light travels from place to place is developed through experiences with light sources, mirrors, and shadows, but no attempt is made to discuss the speed of light.) By the end of grade 5 . A great deal of light travels through space to Earth from the sun and from distant stars. An object can be seen when light reflected from its surface enters the eyes the color people see depends on the color of the available light sources as well as the properties of the surface. (Boundary: This phenomenon is observed, but no attempt is made to discuss what confers the color reflection and absorption properties on a surface. The stress is on understanding that light traveling from the object to the eye determines what is seen.) Because lenses bend light beams, they can be used, singly or in combination, to provide magnified images of objects too small or too far away to be seen with the naked eye. By the end of grade 8 . When light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object s material and the frequency (color) of the light. The path that light travels can be traced as straight lines, except at surfaces between different transparent materials (e. g. air and water, air and glass) where the light path bends. Lenses and prisms are applications of this effect. A wave model of light is useful for explaining brightness, color, and the frequency-dependent bending of light at a surface between media (prisms). However, because light can travel through space, it cannot be a matter wave, like sound or water waves. By the end of grade 12 . Electromagnetic radiation (e. g. radio, microwaves, light) can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features. Quantum theory relates the two models. (Boundary: Quantum theory is not explained further at this grade level.) Because a wave is not much disturbed by objects that are small compared with its wavelength, visible light cannot be used to see such objects as individual Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. Átomos All electromagnetic radiation travels through a vacuum at the same speed, called the speed of light. Its speed in any other given medium depends on its wavelength and the properties of that medium. When light or longer wavelength electromagnetic radiation is absorbed in matter, it is generally converted into thermal energy (heat). Shorter wavelength electromagnetic radiation (ultraviolet, X-rays, gamma rays) can ionize atoms and cause damage to living cells. Photovoltaic materials emit electrons when they absorb light of a high-enough frequency. Atoms of each element emit and absorb characteristic frequencies of light, and nuclear transitions have distinctive gamma ray wavelengths. These characteristics allow identification of the presence of an element, even in microscopic quantities. PS4.C: INFORMATION TECHNOLOGIES AND INSTRUMENTATION How are instruments that transmit and detect waves used to extend human senses Understanding of waves and their interactions with matter has been used to design technologies and instruments that greatly extend the range of phenomena that can be investigated by science (e. g. telescopes, microscopes) and have many useful applications in the modern world. Light waves, radio waves, microwaves, and infrared waves are applied to communications systems, many of which use digitized signals (i. e. sent as wave pulses) as a more reliable way to convey information. Signals that humans cannot sense directly can be detected by appropriately designed devices (e. g. telescopes, cell phones, wired or wireless computer networks). When in digitized form, information can be recorded, stored for future recovery, and transmitted over long distances without significant degradation. Medical imaging devices collect and interpret signals from waves that can travel through the body and are affected by, and thus gather information about, structures and motion within it (e. g. ultrasound, X-rays). Sonar (based on sound pulses) can be used to measure the depth of the sea, and a system based on laser pulses can measure the distance to objects in space, because it is Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. known how fast sound travels in water and light travels in a vacuum. The better the interaction of the wave with the medium is understood, the more detailed the information that can be extracted (e. g. medical imaging or astronomical observations at multiple frequencies). Grade Band Endpoints for PS4.C By the end of grade 2 . People use their senses to learn about the world around them. Their eyes detect light, their ears detect sound, and they can feel vibrations by touch. People also use a variety of devices to communicate (send and receive information) over long distances. By the end of grade 5 . Lenses can be used to make eyeglasses, telescopes, or microscopes in order to extend what can be seen. The design of such instruments is based on understanding how the path of light bends at the surface of a lens. Digitized information (e. g. the pixels of a picture) can be stored for future recovery or transmitted over long distances without significant degradation. High-tech devices, such as computers or cell phones, can receive and decode information and vice versa. By the end of grade 8 . Appropriately designed technologies (e. g. radio, television, cell phones, wired and wireless computer networks) make it possible to detect and interpret many types of signals that cannot be sensed directly. Designers of such devices must understand both the signal and its interactions with matter. Many modern communication devices use digitized signals (sent as wave pulses) as a more reliable way to encode and transmit information. By the end of grade 12 . Multiple technologies based on the understanding of waves and their interactions with matter are part of everyday experiences in the modern world (e. g. medical imaging, communications, scanners) and in scientific research. They are essential tools for producing, transmitting, and capturing signals and for storing and interpreting the information contained in them. Knowledge of quantum physics enabled the development of semiconductors, computer chips, and lasers, all of which are now essential components of modern imaging, communications, and information technologies. (Boundary: Details of quantum physics are not formally taught at this grade level.) Suggested Citation : 5 Dimension 3: Disciplinary Core Ideas - Physical Sciences. National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: The National Academies Press, 2012. doi:10.17226/13165. MyNAP members save 10 online. Login or Register to save Science, engineering, and technology permeate nearly every facet of modern life and hold the key to solving many of humanity s most pressing current and future challenges. The United States position in the global economy is declining, in part because U. S. workers lack fundamental knowledge in these fields. To address the critical issues of U. S. competitiveness and to better prepare the workforce, A Framework for K-12 Science Education proposes a new approach to K-12 science education that will capture students interest and provide them with the necessary foundational knowledge in the field. A Framework for K-12 Science Education outlines a broad set of expectations for students in science and engineering in grades K-12. These expectations will inform the development of new standards for K-12 science education and, subsequently, revisions to curriculum, instruction, assessment, and professional development for educators. This book identifies three dimensions that convey the core ideas and practices around which science and engineering education in these grades should be built. These three dimensions are: crosscutting concepts that unify the study of science through their common application across science and engineering scientific and engineering practices and disciplinary core ideas in the physical sciences, life sciences, and earth and space sciences and for engineering, technology, and the applications of science. The overarching goal is for all high school graduates to have sufficient knowledge of science and engineering to engage in public discussions on science-related issues, be careful consumers of scientific and technical information, and enter the careers of their choice. A Framework for K-12 Science Education is the first step in a process that can inform state-level decisions and achieve a research-grounded basis for improving science instruction and learning across the country. The book will guide standards developers, teachers, curriculum designers, assessment developers, state and district science administrators, and educators who teach science in informal environments. Contents Welcome to OpenBook You re looking at OpenBook, NAP. edu s online reading room since 1999. Based on feedback from you, our users, we ve made some improvements that make it easier than ever to read thousands of publications on our website. Do you want to take a quick tour of the OpenBook s features Show this book s table of contents . where you can jump to any chapter by name. or use these buttons to go back to the previous chapter or skip to the next one. Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book. Switch between the Original Pages . where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text. To search the entire text of this book, type in your search term here and press Enter . Share a link to this book page on your preferred social network or via email. View our suggested citation for this chapter. Ready to take your reading offline Click here to buy this book in print or download it as a free PDF, if available. U. S. Companies Are Stashing 2.1 Trillion Overseas to Avoid Taxes Eight of the biggest U. S. technology companies added a combined 69 billion to their stockpiled offshore profits over the past year, even as some corporations in other industries felt pressure to bring cash back home. Microsoft Corp. Apple Inc. Google Inc. and five other tech firms now account for more than a fifth of the 2.10 trillion in profits that U. S. companies are holding overseas, according to a Bloomberg News review of the securities filings of 304 corporations. The total amount held outside the U. S. by the companies was up 8 percent from the previous year, though 58 companies reported smaller stockpiles. The money pileup, reflecting companies incentives to park profits in low-tax countries, has drawn the attention of President Barack Obama and U. S. lawmakers, who see a chance to tap the funds for spending programs and to revamp the tax code. That effort is stalled in Washington, and there are few signs that tech companies will bring the profits back to the U. S. until Congress gives them an incentive or a mandate. It just makes no sense to repatriate, pay a substantial tax on it, said Joseph Kennedy, a senior fellow at the Information Technology and Innovation Foundation, a policy-research group whose board of directors includes executives from Microsoft and Oracle Corp. Computing and IT companies especially have a lot of flexibility in where they declare their profits. Apple, Google Microsoft, Apple and Google each boosted their accumulated foreign profits by more than 20 percent over the year, the largest increases by any of the 34 companies with at least 16 billion outside the U. S. International Business Machines Corp. Cisco Systems Inc. Oracle, Qualcomm Inc. and Hewlett-Packard Co. each added at least 4 billion. The profits added by the eight technology companies accounted for 45 percent of the net gain in overseas funds among the corporations surveyed. At the same time, firms in some other industries felt enough pressure to meet domestic needs that they chose to take the tax hit by bringing money home. Duke Energy Corp. based in Charlotte, North Carolina, took a 373 million tax charge against earnings in February as part of a plan to get access to 2.7 billion in accumulated foreign profits. Stryker Corp. a Kalamazoo, Michigan-based maker of medical devices, is planning to repatriate 2 billion this year. Apache Corp. a Houston-based oil and gas company, had 17 billion indefinitely reinvested overseas at the end of 2013. Now, it has none. The company made the decision to utilize international cash to pay down U. S. debt and grow its North American operations, Castlen Kennedy, a spokeswoman, said in an e-mail. GE Leads General Electric Co. topped the list for the fifth straight year. The company now has 119 billion outside the U. S. an increase of 8 percent from the end of 2013 and a 27 percent gain since 2010. By contrast, Microsoft has more than tripled its offshore holdings since 2010. Apple, which counts only part of its non-U. S. holdings as indefinitely held offshore, increased that portion to 69.7 billion from 12.3 billion in 2010. Cisco now has 52.7 billion outside the U. S. up 10 percent since 2013. Microsoft referred back to 2012 Senate testimony by Bill Sample, its vice president for worldwide tax. Sample said then that the Redmond, Washington-based company is fundamentally a global business and that U. S. law creates a disincentive for U. S. investment. Kristin Huguet, a spokeswoman for Cupertino, California-based Apple, declined an interview request. Google Needs Google referred to a December 2013 letter that the Mountain View, California, company sent to the Securities and Exchange Commission. It said Google needs 20 billion to 30 billion for future acquisitions outside the U. S. 12 billion to 14 billion for foreign subsidiaries share of developing intellectual property and 2 billion to 4 billion for capital expenditures. John Chambers, Cisco s chief executive officer, said on Bloomberg TV on Feb. 20 that his company is investing in India, Israel and France in the absence of U. S. tax law changes. I d prefer to have the vast majority of my employees here, Chambers said. And our tax policy is causing me to make decisions that I don t think is in the interest of our country, or even in our shareholders, long term. The Bloomberg analysis covers 304 large U. S.-based companies that are required to report annually how much they hold outside the country in profits, which isn t the same thing as cash. Won t Repatriate It s a measure of accumulated profits, including those reinvested in active businesses and factories. The companies say they won t repatriate these profits, and they haven t assumed that they will pay future U. S. taxes that would be owed if they did. One of the reasons that they re holding the hoards of cash abroad is they don t want to pay the repatriation tax when they bring it back, said Rosanne Altshuler, a Rutgers University economist who studies international taxation. The analysis starts with corporations in the Standard Poor s 500 Index and excludes purely domestic firms, real estate investment trusts and companies with headquarters outside the U. S. It includes each company s most recent annual report, many of which were filed over the past month. The companies owe taxes at the full U. S. corporate tax rate of 35 percent on profits they earn around the world. They get tax credits for payments to foreign governments and don t have to pay the residual U. S. tax until they bring the money home. Offshore Incentive Keeping money overseas is particularly easy for technology and pharmaceutical companies whose profits stem from intellectual property that can swiftly be moved. It s very easy to place a patent in another country and accrue the income there, Altshuler said. They re very sensitive to differentials in corporate tax rates. Gilead Sciences Inc. for example, reported that it held 15.6 billion outside the U. S. as of Dec. 31, up from 8.6 billion a year earlier. That s because the intellectual property for the company s blockbuster drug -- Sovaldi -- was in Ireland before the Food and Drug Administration approved it in 2013. Corporations that rely on intellectual property -- trademarks, logos or patents -- have an advantage over heavy industrial companies and the financial industry, which relies on providing services to customers, said Jennifer Blouin, an associate professor of accounting at the University of Pennsylvania s Wharton School. You can t move an oil rig out of certain jurisdictions, she said. You can t shift the service income without moving the people. Shareholder Obligation Companies have a duty to their shareholders and they re responding logically to the incentives in the system, Kennedy said. Companies are strongly driven by the need to increase shareholder value, and especially any public company has to meet market expectations, he said. Whatever the reasons, the potential tax revenue from offshore profits is tempting to U. S. lawmakers, who have been struggling to fund road projects and revamp the tax system. Obama and top Republicans on the tax-writing committees say they won t repeat a 2004 law that gave companies a voluntary repatriation holiday with a 5.25 percent tax rate. Instead, Obama earlier this year proposed applying a 14 percent mandatory tax on the stockpiled profits and a 19 percent minimum tax on foreign earnings going forward. The one-time tax would generate 268 billion over six years, which Obama wants to use for infrastructure. Because the one-time transition tax is levied on past earnings, it doesn t distort companies decisions, Altshuler said. The real questions are the rate and the details of the tax system for future earnings. Obama s plan hasn t advanced in Congress, amid Republican objections to some of the details and the idea of using one-time money for needs such as highway construction. The president met March 2 with the chief executive officers of Xerox Corp. Micron Technology Inc. Qualcomm, IBM and EMC Corp. which have a combined 114 billion in accumulated offshore profits. The president and the executives also discussed a shared desire to work with Congress to enact pro-growth, business tax reform, the White House said in a statement. That doesn t mean it s going to happen anytime soon. Antes de que esté aquí, está en la Terminal de Bloomberg. APRENDE MÁS
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