Physices help about increase in frequency???

Question

In a experiment i had to determine how the length of a pendulum affects the time of each swing.

i tried it for 20 seconds i got 40 swings first time and 32 swings when i shorten the string in the same time

does that seem like good results or should I try it again??

Because it sounds off relating back to the formula??? any help, 10 points for good answer

Answer 1

The period of the oscillation should decrease as you shorten the length of the pendulum, meaning it should swing faster. The formula that you are probably using, T=2pi sqrt(l/g), is only valid for small amplitude oscillations, where the approximation sin(x)=x is close to being correct. I think that when you did the experiment you likely had significantly different amplitude of swing for the two trials. Start each oscillation with the string at the same angle to the ground and you should get better results. Also, repeat the measurement more than once for each string length to see if your numbers stay the same.

Answer 2

Either your timing (20 seconds) is off or your count is off. As the string gets short, the number of swings should be greater.

Stop fooling with half inch changes... Do a count when the string is 3 feet long and then do a count when the string is 6 inches long!

You point will then be proved.