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# Whirling Bung Experiment - why does the weight move up? Watch

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1. Now, I know that as the bung is swung in a horizontal circle, the suspended weight remains stationary as long as the force provided (Mg) is equal to the centripetal force required to make the bung travel in its circular path.

However, my book later says

If the centripetal force required is greater than the weight, then the weight moves upwards.

I know this would increase the radius in the formula F = mv^2 / r
but it does not make sense how this happens.

Can someone explain why?

I thought since a = v^2 / r, a greater v would mean a larger r is required, hence the weight moves up to give a greater radius from the string.

Is that correct?
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2. (Original post by nwmyname)
Now, I know that as the bung is swung in a horizontal circle, the suspended weight remains stationary as long as the force provided (Mg) is equal to the centripetal force required to make the bung travel in its circular path.

However, my book later says

If the centripetal force required is greater than the weight, then the weight moves upwards.

I know this would increase the radius in the formula F = mv^2 / r
but it does not make sense how this happens.

Can someone explain why?

I thought since a = v^2 / r, a greater v would mean a larger r is required, hence the weight moves up to give a greater radius from the string.

Is that correct?
well in this demo the force is a constant so if you increase v then r will increase (i.e. move the weight upwards) until you reach a new equilibrium position... btw this isn't like planets orbiting round the sun because the gravitational force varies as 1/r2

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