# Homework Help: Why don't we have to know the hight at which a pendulum is dropped to get the period?

1. Jul 18, 2012

### student34

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

What's the period to a 1 meter long physical pendulum string where L = 1M
T=2∏√((2L)/(3g)) = 1.64s

But, I did my own experiment, and the higher I dropped the pendulum the longer it took for it to travel 1 oscillation. What is going on here?

2. Relevant equations

3. The attempt at a solution

2. Jul 18, 2012

### TSny

Re: Why don't we have to know the hight at which a pendulum is dropped to get the per

Hi student34. The formula that you are using is only an approximate formula. It's pretty accurate for small amplitude oscillations (the smaller the better), but becomes more and more inaccurate as the amplitude is increased. See http://en.wikipedia.org/wiki/Pendulum

3. Jul 18, 2012

### student34

Re: Why don't we have to know the hight at which a pendulum is dropped to get the per

Thank you so much. I thought I was going crazy!!!