# Homework Help: Torsional Pendulum Experiment Help

1. Jul 31, 2012

### yaluubill

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

In physics class, we were given a task to investigate a factor that affects the period of a torsional pendulum.

I imagined having a setup where a massless rod would be suspended horizontally from a retort stand using a string secured to the middle of the rod so it would balance. At the ends of the rod would be two equal weights.

I.V. - Weight of mass m on either side of the rod
D.V.- Time period for one cycle
C.V.- length of string, length of rod, material weight (e.g. surface area, shape) force exerted making it oscillate[?]

Assumptions:
- rod is massless (is using a BBQ stick ok?)
- energy lost to friction is negligible
-
￼￼￼￼

2. Relevant equations
We know that:
T = 2∏√l/k
where l in this situation is = 2[mr^2)

I expect to see an directly proportional graph where an increase of mass m would result in greater time T.

I'm planning to calculate for constant k when I do the experiment proper itself so that it would be the constant for the set conditions the experiment is carried out in.

3. The attempt at a solution
I know that measuring multiple oscillations and getting an average would yield more accurate results than just measuring one cycle.

I don't have any idea though how to construct the setup such that the rod with the two masses on either end would turn one way (clockwise) and then without losing significant energy, turn the other (counter-clockwise).

I tried testing a similar setup with a rubber band and pencil where the pencil was inserted between the inner sides of the rubber band. It was then twirled 10 times, and when released, the rubber band unfurled and the pencil flew off.

Would someone be able to suggest possible materials I could use that better preserve the energy, and also possible weights I could use given that the rod should be massless (or super light in the experiment... initially I was thinking of similar clay balls that would be skewered with the BBQ stick).

If ever, would another setup possibly be more practical? more doable? (especially since its for a high school physics class [IB Senior Physics]

Thank you so much!

Last edited: Jul 31, 2012
2. Aug 1, 2012

### Staff: Mentor

http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

Hi yaluubill. String may not be a good material for a torsional pendulum. Try a monofilament such as wire. Have you done a google search? I'd look on youtube, too, there's sure to be some demos there.

Last edited by a moderator: May 6, 2017
3. Aug 1, 2012

### yaluubill

Thanks a bunch! I'll definitely look into that

Last edited by a moderator: May 6, 2017