Section 6.4Potential Energy

Potential Energy How can I calculate the potential energy?

Potential Energy Potential Energy depends on an object’s surroundings

Depends on position or configuration

Examples A wound up spring

A stretched elastic band

An object at some height above the ground

Potential Energy Raising a mass m to a height h

Work done by the external force (gravity)

Potential Energy

you will also see mgh

Change in PE is important

Be sure to set your original = 0 and be consistent, since we are measuring change in PE

Potential Energy PE can become KE if the object is dropped

PE is the property of a system as a whole since it depends on external forces

Example A 1000 kg roller coaster car moves from point 1, to point 2 and then point 3.

(a) What is the gravitational potential energy at 2 and 3 relative to point 1? Take y = 0 at point 1.

Example (b) What is the change in potential energy when the car goes from point 2

to point 3?

Spring Potential Energy Potential energy can also be stored in a spring when it is compressed

As it is released, the energy changes to kinetic

Spring Potential Energy The force required to compress or

stretch a spring:

K is the spring constant, specific to each spring

Elastic PE The forces increases as the spring is

stretched or compressed

Potential energy of the compressed or stretched spring, measured from its equilibrium position is:

Homework Page 163

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