Energy & simple Pendulum (short lab)
Does it loop-the-loop?
Using Conservation of Energy
Consider the following pendulum set-up. A ball of mass m is attached to a
string of length L, and is pulled so that the ball is an initial height h0
from the lowest point in its swing. A rod is clamped at a height h above the
lowest point so that when the pendulum swings down, the string wraps around
the rod, and the ball swings around in a circle of smaller radius.
Your challenge (pre-class):
1. Determine the smallest height h0 from which the ball can be released
in order that it complete the small circle without the string going slack.
Show clearly how you derived the value of the initial height, h0, in terms
of the height h.
2. Checking your answer (in class):
You will be provided a simple pendulum and can measure its length L. Set up
the experiment so that the rod is at a height h = L/4.
(a) Does your predicted value succeed?
(b) If not, figure out why not: is it your derivation? is it your measurements? is it the equipment available?
(c) Can you simulate it in interactive physics and get your answer to work?
[If you do this, make certain you show these results to the instructor.]
From the student server, copy the file “PendulumVL” into the “My
Documents” folder on your computer. This is a starting point for your
verification. I would think about what kinetic energy your original height
predicts for the object at the top of its path and what actual energy is required
in order for the string to be taut. [I have not found any way to make the
string wrap around a rod (as we do experimentally), but I am not an expert
at this. If anyone does figure out a way, be certain to let me know.]
Now, does your predicted value succeed?
If yes, go on to next part. If no, figure out why not: is it your derivation? is it the settings in Interactive Physics?
(d) In what ways does your actual experimental set up differ from the ideal?
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This page maintained by Anne G. Young. Last modified 22-Jan-2004 .