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Electric ARC #8 : Crazy Pendulum

By on Feb 1, 2007 in Personal | 0 comments

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An interesting physics problem to try out:

Say there’s a pendulum. Assume dissipative forces are absent. Extreme positions are A and C, mean position is B. It is taken to an extreme position, and released. When it reaches the mean position, gravity is ‘switched off’. What will happen to the motion of the pendulum bob?

And the answer is…

At the lowest point the string tension T = mg + mv2/L. When g is switched off, mg becomes zero. Thus, T = mv2/L. The velocity does not change as there is no force component in the tangential direction. So, T does not change, thus providing for centripetal acceleration in perpetuity. Conclusion – the bob moves in a circle with uniform speed, indefinitely.

…that is, unless it hits the ceiling… ;)



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