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Gravitometer?


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After the recent Science Week post I drove past York today and noticed that the river was very high. Must be high tide methinks. Then I wondered what would happen if you hung a weight off a whole load of elastic bands from something very high. Would the weight go up and down in response to where the moon is like the tide does, or is the effect too feeble to measure? Anybody know how to do the sums?

Captain Chaos

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Not sure about the tides, but I know that people have measured gravity before. They have however used multi-ton blocks of aluminum suspended from very sensitive sensors. I think you'de need a LARGE block of aluminum to have a measurable change due to the moon. I'm sure the maths are fairly simplistic though given the mass of the moon, the mass of your block of ali and the distance.

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So, for a 1kg mass:-

Fg=(6.67x10^-11 X 1 X 7.35x10^22)/(3.75x10^8)^2

Fg=0.03mN

Not a lot really, is it?

If the elastic stretched 10M because of the 1kg mass (near enough 10N), then for each Newton of force it would move 1M. The change in direction of the gravitational force from the moon would give twice the above as it would go from pulling up to pulling down, so the movement would be 0.03mm. Not really workable, is it?

Thanks for the formula Gordon.

Captain Chaos

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