**Elastic Potential Energy**

– Many objects can stretch, compress or bend (ex. diving board)

– Once the force that was applied to it is removed, some objects can return to its original shape

– This suggests that there was energy stored in the object due to its condition- known as **Elastic Potential Energy**

**Hooke’s Law**

– Springs are an example of a type of object with elastic potential energy

– When a force causes a spring to stretch, the spring exerts a force in a direction that will return it to its original length

– This is known as a **restoring force**

– Always acts in a direction opposite that in which the spring is stretched or compressed

– Property of elastic objects is known as Hooke’s Law

– **Hooke’s Law:** The applied force is directly proportional to the extension or compression of a string

– The data produces a straight line with the equation y=mx+b where m is the slope and b is the y intercept

o The slope of a line describing a spring is known as the **spring constant (k)**

o Spring constant is in the unit N/m

o Each spring has its own constant; it tells us the amount of force that is necessary to stretch or compress the spring a given amount

o The zero position is generally designated to the spring when there is no force applied (thus the y intercept is zero)

Hooke’s Law

F_{a}= -kx

Fa= force applied (N)

K= spring constant (N/m)

X= amount of compression or stretch (m)

The equation is negative because the restoring force always acts in opposite direction of the displacement (x)

Elastic Potential Energy

The elastic potential energy of a perfectly elastic material is ½ of the product of the spring constant and the square of the length of extension or compression.

E_{e}= ½kx^{2}

For homework, please complete:

Page 258, #35-37

Page 261, #38-40, Section Review Questions 7, 9