1. Elastic Force and Energy Stretching or Compressing a spring causes the spring to store more potential energy. The force used to push or pull the spring causes the spring to become shorter or longer.

2. Answer Me!!! Why does a rubber band fly across the room when stretched out and released?

3. Hooke’s Law The force (F) you put on a spring equals the spring constant (k) times the distance the spring is stretched (x) from equilibrium. F s = kx The spring constant is a measure of a springs response to stretching or compressing. Spring constant is measured in N/m.

4. Elastic Potential Energy Elastic Potential Energy (PE s ) is the energy stored in an elastic system (spring) due to a distortion (x). Elastic Potential Energy is measured in Joules The spring constant is a reflection of many characteristics of the spring’s composition.

5. Practice Problem 1 A 10 N force is required to hold a stretched spring 0.20 m from its rest position. What is the spring constant?

6. Practice Problem 2 The graph shows elongation as a function of the applied force for two springs, A and B. Compared to the spring constant of A, the spring constant of B is_____________.

7. Practice Problem 3 A 10 N force is required to hold a stretched spring 0.20 m from its rest position. What is the potential energy stored in the stretched spring?

8. Practice Problem 4 A spring of negligible mass has a spring constant of 50 N/m. If the spring is stretched 0.40 m from its equilibrium position, how much potential energy is stored in the spring?

9. Final Thought… A student compresses the spring in a pop-up toy 0.020 m. If the spring has a spring constant of 340 N/m, how much energy is being stored in the spring?

10. Answer Me!!! A 0.50 m long spring is stretched to 1.00 m by a weight. If 15 J of energy are stored in the spring, what is the value of the spring constant?

11. Final Thought… Draw the graph that represents the elastic potential energy stored in a spring (PE s ) as a function of its elongation, x.