# Homework Help: A simple yet tricky pendulum problem

1. Nov 15, 2008

### Mr.P

1. The problem statement, all variables and given/known data

A swing in a playground is set in motion without anyone on it. Thereafter a person sits on it, as close to static as possible while the swing is in motion.
Finally a person is standing on the swing, the swing in motion.

2. Relevant equations

Under ideal circumstances (no aerodynamics, no movement by the person etc), in what case would the frequency of the "harmonic pendulum" be the highest?

3. The attempt at a solution

The frequency should be the highest in the case with the person standing on the swing, since the centre of gravity has moved further up. With noone on the swing the frequency should be somewhat lower, and lowest with a person sitting on since the gravity then is moved downwards.
What do you think, all help is appreciated.

/Mr.P
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 15, 2008

### LowlyPion

Welcome to PF.

When the person is sitting how much of their weight is above the seat and how much below?

The center of mass then is higher or lower than the swing alone?

3. Nov 16, 2008

### Mr.P

There is no info on how the centre of mass is moved compared to the seat of the swing. Nor is there any info on how the persons weight is divided. But if I am not mistaken the centre of mass in a human is located in the very low stomach. Assuming this is correct, the centre of mass should be higher with a person sitting on the swing than for the swing alone.
If this is the case the frequency for the swing is the lowest for the swing itself, higher with a person sitting on it and the highest with a person standing on it.
Would this seem reasonable to assume?
As the title of the question hint it feels like a tricky problem..

Pete

4. Nov 16, 2008

### LowlyPion

That sounds like a better answer then.

Cheers.

5. Nov 16, 2008

### Mr.P

Thanks for the time LowlyPion, feedback much appreciated.

Pete