Hooke’s Law and

Elastic Potential Energy

• Springs have PE when compressed or stretched (it can do work on an object)

F= -kx • The amount the spring is compressed/stretched from

the normal is x• k is the spring constant: a measure of strength• The spring exerts its force in the opposite direction of

the displacement (negative sign)• Force increases with distance (x)

Hooke’s Law

Was that bad physics?

•How did applied force and the restorative force compare?

EPE = ½ kx2

http://www.pbs.org/opb/circus/classroom/circus-physics/activity-guide-conservation-energy/

Elastic Potential Energy(spring energy)

• A toy dart has a mass of 100 g and is pressed against a toy dart gun with a spring 6 cm and released. The spring constant is 250 N/m. How much potential energy is present?

• The dart detaches from the spring and the spring reaches its normal (x). What maximum speed can the dart attain?

• A ball with a mass of 2.60 kg starts from rest and falls 0.55 m vertically before striking a coiled spring, which it compresses 15 cm. Determine the spring constant of the spring.