# Pendulum/planet circular motion

1. Jul 15, 2007

### mintyyf

The motions of a pendulum and a planet undergoing circular motion are compared.
a. describe the simularity in their motions
b. describe a difference in there motions.
c. Outline a difference in the force(s) acting on the pendulum and the planet.

this is kind of a stupid question and i have no idea where to even start. the only thing i can think of is that both the pendulum and planet are having the force of gravity some how workin around them. if you can help thanks a bunch!

2. Jul 16, 2007

### andrevdh

If you consider the projection of the motion of the planet onto "the x-axis" one can see a similarity between the two types of motions.

3. Jul 16, 2007

### LHarriger

I could be wrong, but it is likely you should consider the motion of the pendulum in the abscense of gravity. You will still find that both the planet and pendulem experience a central force. You should discuss how these central forces differ in origin and magnitude. There is also a fictitious force at play. What is it? Is it different for each case? What is its origin? How do they affect the equation of total energy, etc...