1. Elastic Potential Energy
Topic 4

2. Elastic Potential Energy
The energy available for use in deformed elastic objects
Rubber bands, springs in trampolines, pole-vault poles, muscles
For springs, the distance compressed or stretched = x
Point out that x in the diagram is the “Distance compressed.” This will be used in the equation for elastic potential energy (slide 10).
Discuss the transfer of the elastic potential energy to the block when the deformed spring returns to its original configuration.

3. Spring Constant (k)
Click below to watch the Visual Concept.
Visual Concept
The spring constant (k) depends on the stiffness of the spring.
Stiffer springs have higher k values.
Measured in N/m
Force in newtons needed to stretch a spring 1.0 meter

4. Elastic Potential Energy
PEspring = kx2
k = the spring constant (N/m)
x = the distance the spring is stretched (m)
What are the SI Units for PEelastic?
Joules (J) (N·m)
The joule is the SI unit for any form of energy
Help students find the SI units as N•m or Kg•m2/s2 or J.
Now would be a good time to remind them that work, KE, and PE are all measured in joules (kg•m2/s2).

5. Classroom Practice Problems
When a 2.00 kg mass is attached to a vertical spring, the spring is stretched 10.0 cm such that the mass is 50.0 cm above the table.
What is the gravitational potential energy associated with the mass relative to the table?
Answer: 9.81 J
What is the spring’s elastic potential energy if the spring constant is N/m?
Answer: 2.00 J
Point out to students that the zero level is at the table for gravitational PE. Also, they must use meters, not centimeters, in order to have joules as units in the final answers.