Energy as Motion and Fields
Aligned to HS-PS3-2 — Next Generation Science Standards.
What this lesson teaches
At the large scale, energy can be tracked two ways: as the kinetic energy of moving particles (motion and temperature) or as potential energy stored in fields (gravitational, electric, magnetic, or chemical bonds). A total energy account stays balanced as energy shifts between these forms.
Worked examples
Example 1
A 2 kg book held 1.5 m up stores gravitational potential energy PE = mgh = 2 x 9.8 x 1.5 = 29.4 J in the Earth-book field. When dropped, that field energy converts to kinetic energy of the falling book, so it arrives moving with 29.4 J of kinetic energy (ignoring air).
Example 2
Double the height and you double the stored energy; double the speed and you quadruple the kinetic energy. The two are not symmetric.
Example 3
Potential energy belongs to the system, not the object. The book alone has none — the energy is in the Earth-book pair.
Practice questions
- Classify each as field-stored or particle-motion energy: a hot cup of coffee, a stretched rubber band, a charged battery.
- Calculate the potential energy stored when a 5 kg mass is lifted 3 m.
- Trace the energy of a swinging pendulum through one full swing, naming where it is field-stored versus motion energy at each point.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
La Energía como Movimiento y Campos
A gran escala, la energía se puede rastrear de dos maneras: como energía cinética de partículas en movimiento (movimiento y temperatura) o como energía potencial almacenada en campos (gravitacional, eléctrico, magnético o enlaces químicos). Un balance total de energía se mantiene mientras la energía cambia entre estas formas.
Ejemplo 1: Un libro de 2 kg sostenido a 1.5 m de altura almacena energía potencial gravitacional EP = mgh = 2 x 9.8 x 1.5 = 29.4 J en el campo Tierra-libro. Al soltarlo, esa energía del campo se convierte en energía cinética del libro que cae, así que llega moviéndose con 29.4 J de energía cinética (sin contar el aire).
Ejemplo 2: Duplica la altura y duplicas la energía almacenada; duplica la rapidez y cuadruplicas la energía cinética. Las dos no son simétricas.
Ejemplo 3: La energía potencial pertenece al sistema, no al objeto. El libro solo no tiene ninguna — la energía está en el par Tierra-libro.
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