1. Ch. 12
Waves
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2. Hooke’s Law Periodic motion – a repeated motion
Ex. A mass attached to a spring

7. Hooke’s Law
The force always acts toward the equilibrium position – This is called the restoring force
At the equilibrium position, velocity reaches a maximum
At the maximum displacement, the elastic force and acceleration reach a maximum

8. Hooke’s Law
The direction of the spring force and the acceleration is opposite from the direction of motion
The spring force is directly proportional to the displacement of the mass

9. Hooke’s Law Without friction, the spring would oscillate indefinitely
Friction causes the spring to eventually come to rest, this effect is called damping

10. Hooke’s Law Spring Force units = N Spring Constant units = N/m
Displacement units = m

11. Hooke’s Law
Negative sign means direction of the spring force and the direction of the displacement are opposite
Spring constant (k)
A measure of the stiffness of the spring
A large k indicates a stiff spring
A small k indicates a soft spring
Displacement (x)
x = 0 at the equilibrium position

12. Simple Harmonic Motion
Any periodic motion that is the result of a force that is directly proportional to displacement
A back and forth motion over the same path
The motion of a spring mass system is an example of Simple Harmonic Motion

13. Simple Harmonic Motion
Not all periodic motion over the same path can be considered Simple Harmonic Motion
To be Simple Harmonic Motion, the force must obey Hooke’s Law

14. Elastic Potential Energy
A compressed or stretched spring has potential energy
The compressed spring, when allowed to expand, can apply a force to an object
The potential energy of the spring can be transformed into kinetic energy of the object

15. If a mass of 0.55 kg attached to a vertical spring stretches the spring 2.0 cm from its original equilibrium position, what is the spring constant?