# Homework Help: Pendulum measuring the restorative force HELP

1. Apr 12, 2010

### milk242

Pendulum measuring the restorative force HELP!!

1. The problem statement, all variables and given/known data
A pendulum with length L is suspended at an angle theta. At the bottom of the pendulum, a string is attached to force meter. The string attached to the force meter is perpendicular to the pendulum string. In terms of F and theta, find an expression for mass.
2. Relevant equations
Fg= -mg
(Fg)r = -mgcos(theta)
(Fg)t = -mgsin(theta)

3. The attempt at a solution
What I get is all the tangential and radial components cancel out equally zero, which I would expect because mass doesn't matter in a pendulum. So I don't understand how I'm suppose to obtain an expression for mass.

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2. Apr 12, 2010

### rl.bhat

Re: Pendulum measuring the restorative force HELP!!

Hi milk242, welcome to PF.
Radial force due to mg is balance by the tension in the string. Where as the tangential force is an unbalanced force which tries to bring the bob to the equilibrium position.
Your force meter measures this force, which is perpendicular to the string.

3. Apr 12, 2010

### milk242

Re: Pendulum measuring the restorative force HELP!!

Thanks for your help! I got it now.