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Unit 4

# 4.3 Conservation of Energy, the Work-Energy Principle, and Power

Peter Apps

### AP Physics 1Β π‘

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## Enduring Understanding 5.B π¨βπ»

The energy of a system is conserved.
When a system has no work being done on or by it, the total energy of the system is constant. This total energy can be internally converted among potential, kinetic, or thermal but never changes. This idea is the Law of Conservation of Energy and is one of the 4 major conservation laws in AP 1.
A key idea here is that this law only applies when there are no outside forces acting on the system. So a system consisting of a ball and the earth would have its energy conserved as the ball falls, but a system of a car would have its energy change as friction between the tires and the road removes kinetic energy.
Common situations where youβll be asked to apply energy conservation include: falling objects, sliding or rolling down ramps, masses & springs, and planetary orbits.
To help visualize this conservation, watch the roller coaster below (no friction).

Image courtesy of PhysicsClassroom.

In this case, the TME is the total mechanical energy, or potential plus kinetic energies. Most of the time, when a question refers to the total energy, we really mean total mechanical energy.
π₯Watch: AP Physics 1 - Unit 4 Streams

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