1. Elastic Potential Energy

2.  Elastic Potential Energy (EPE) is a measure of the restoring force when an object changes its shape

3. Compression and Extension  It takes force to press a spring together.  More compression requires stronger force. extend  It takes force to extend a spring. force  More extension requires stronger force.

4. Stretched or Compressed  Elastic potential is gained whether the spring is stretched or compressed

5. Change in Potential Energy  The distance (x) stretched or compressed determines the change in potential energy of the spring

6. Meaning of Elastic  Elastic means the object will return to its original shape when the force is removed.

7. Hooke ’ s Law  The force from the spring attempts to restore the original length. This force is called the restoring force.  This is also called Hooke’s law. L+ x L - x L

8. Scales  One common use for a spring is to measure weight.  The displacement of the spring measures the mass. -y F g = -mg F s = -k(-y)

9. Other Forms of Elastic Potential  A ball when it bounces on the ground  A catapult pulled back to launch a stone  A crossbow ready to fire an arrow

10. EPE to GPE Conversion/Conservation  A 30 kg child pushes down 15 cm on a trampoline and is launched 1.2 m in the air.  Elastic potential energy is created by the stretch of the trampoline.  Then the child has all kinetic energy, which becomes all gravitational energy at the top of the jump.  The energy is conserved.