Periodic Motion Simple Harmonic Motion is a repeating motion or an oscillating motion that has a point where the net force acting on the object is 0N. Examples: Swinging on a swing set A guitar string A weight on a spring Bungee Jumping! Pendulums

Periodic Motion As an object falls it is accelerated down by the force of gravity. When tethered to a spring (or bungee cord) and it begins to stretch beyond where it would normally hang it applies a force in the opposite direction. It will continue to increase until the applied force of the spring exceeds the force of gravity, at which point the object will begin to accelerate upward again. Each time the object oscillates up and down it passes the equilibrium point where F g = F s. Hooke’s Law

Centripetal Forces: Pendulums! A pendulum oscillates back and forth in a specific time, T, due to gravity. recall: so: and: finally: g = 9.8 m/s 2 T = Time period r = length (l) of pendulum g T : time from start to end back here. l = length of pendulum

Pendulum Motion Problems: 1. A child on a swing set rocks freely back and forth because of gravity. The length of the chain swing is 3.04m. How long does it take for one oscillation? 2. A wall mounted cuckoo clock (small) has a pendulum with a time period of 1 second. What is the length of the pendulum? 3. A tall grandfather clock has a 2m long pendulum. What is it’s Time period? Pendulum Lab, PS8B