Pendulums

Definition

• Simple Pendulum – Massive object, called a bob, suspended by a string or

light rod of length, l.• Periodic Motion – Motions that repeat in

a regular cycle

Terms to Describe Pendulums

• Period (T) – time needed for an object to repeat one complete cycle of motion

• Amplitude (A) – maximum distance that the object moves from equilibrium (start)

What affects the period of a pendulum?

• The only variable that affects the period of a pendulum is the length of the string.

l

How do I find the Period?

• T = Period

• l = length of string

• g = acceleration due to gravity, 9.81 m/s2

• = 3.14

g

lT 2

Uses of Pendulum?

• Timekeeping

Uses of Pendulum?

• Determination of Gravity (9.81 m/s2)

Uses of Pendulum?

• Rotation of the Earth

• But How?

Foucault’s Pendulum

• Jean Bernard Leon Foucault – Set up a pendulum and noticed that it

shifted places as it swung!

– http://en.wikipedia.org/wiki/Image:Foucault-anim.gif

– It shifted around 270o in 24 hours!

– Proving that the earth was rotating around on its axis.

Example

• A pendulum is made on Earth with a 40 g mass and a 2 m long string. What will be the period of the pendulum????

On Your Own

• A pendulum on Earth has a length of 5 m. What is the period of this pendulum?

Challenge

• George went to Planet Z and made a pendulum. His pendulum was 4 meters long and George found that it had a period of 4.012 seconds per swing. What is the acceleration due to gravity on Planet Z?