Energy Transfer Changes Motion
Aligned to MS-PS3-5 — Next Generation Science Standards.
What this lesson teaches
An object's kinetic energy changes only when energy is transferred to or from it, usually by a force doing work. The energy is never lost — it just moves between objects or forms.
Worked examples
Example 1
When a soccer ball rolls to a stop, its kinetic energy does not vanish — friction transfers that energy to the ground and air as thermal energy, warming them slightly.
Example 2
A dropped ball never bounces back to its original height, because some energy leaves as sound and heat each bounce.
Example 3
Energy is conserved but it is not always recoverable. The heat that friction spread into the ground cannot be gathered back into motion.
Practice questions
- Observe a ball speeding up down a ramp and identify where its added energy came from.
- Construct an argument, using evidence, that a slowing sled is transferring energy away.
- Explain why a moving object cannot speed up unless energy is transferred to it.
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 Transferencia de Energía Cambia el Movimiento
La energía cinética de un objeto cambia solo cuando se le transfiere energía o se le quita, normalmente por una fuerza que realiza trabajo. La energía nunca se pierde — solo se mueve entre objetos o formas.
Ejemplo 1: Cuando una pelota de fútbol rueda hasta detenerse, su energía cinética no desaparece — la fricción transfiere esa energía al suelo y al aire como energía térmica, calentándolos un poco.
Ejemplo 2: Una pelota que sueltas nunca rebota a su altura original, porque algo de energía se va como sonido y calor en cada rebote.
Ejemplo 3: La energía se conserva pero no siempre es recuperable. El calor que la fricción esparció en el suelo no se puede juntar de vuelta en movimiento.
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