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Conservation of Mechanical Energy |
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| Sep5-04, 12:42 AM | #1 |
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Conservation of Mechanical Energy
I watched [Lecture 13] of the Newtonian Physics class in here . On the last part of the lecture, they did 2 experiments on pendulums (conservation of mechanical energy, etc.) and the first experiment followed the prediction however, the 2nd experiment did not follow the prediction.
I have thought about it and are unable to come up with an answer, I hope you guys can give me a hint. |
| Sep5-04, 01:02 AM | #2 |
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I looked in the index rather than sat through the video - was this problem related to the difference between the equations of motion of a sliding puck and a rolling ball?
If so, you might want to think about the moment of inertia of the ball. |
| Sep5-04, 01:08 AM | #3 |
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the experiment was done during the end of the video ...
anyways - thanks for the hint - i will think about it. |
| Sep5-04, 01:14 AM | #4 |
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Conservation of Mechanical Energy
That's way too long to watch - just tell us about the experiments.
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| Sep5-04, 01:14 AM | #5 |
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oh - oops - actually it wasnt on the puck and the rolling ball
it was the last thing on http://ocw.mit.edu/OcwWeb/Physics/8-...x-for-L-13.htm "The known radius of a circular air track is used to predict the period of oscillation of a sliding object (small angles!), and a measurement is made to confirm this. The process is repeated for a ball bearing rolling in another circular track. The period of oscillation can now not be predicted in a similar way as was possible in the case of the air track. Why? ==> No, it has nothing to do with friction! " |
| Sep5-04, 01:16 AM | #6 |
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| Sep5-04, 01:18 AM | #7 |
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Yes - but I'm working with low bandwidth and it will take ages to get there.
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| Sep5-04, 01:23 AM | #8 |
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experiment #1: an object is put on the air track with a radius of ~115m and was released at the starting point and the professor predicted the period using the principles of mechanical energy and simple harmonic oscillation. experiment #2: an ball is put on a curvature much smaller than the air track radius ~85cm and it was tested using the same principle of experiment #1 but the result did not agree to the prediction. |
| Sep5-04, 01:25 AM | #9 |
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btw - it's better to watch the experiment yourself since i might miss some detail ...
and pervect said that it might be through the rotation of the ball - but i am not quite sure... |
| Sep5-04, 01:34 AM | #10 |
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From what you described, pervect's explanation sounds right on!
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| Sep5-04, 02:32 AM | #11 |
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The moment of inertia for a sphere (solid & uniform) is [itex]\frac{2}{5}Mr^2[/itex] which would increase the period by a factor of about [itex]\sqrt{1+\frac{2}{5}}[/itex]. |
| Sep6-04, 04:10 AM | #12 |
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ok thanks.
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