# Less gravity (perceived) when moon overhead?

Hi, when the moon (or sun) is overhead do they alleviate the earths pull on you to the extent that you could jump a bit higher or is it balanced out somehow? Like how the tides rise and fall due to moons pull. If a weighing scale was unaffected by the pull would you weigh less when moon overhead?

virtually yours,

Virtually Yours

The difference is real, but not really perceptible compared to Earth’s gravity. By my calculations the gravitation effect exerted by the moon upon something on Earth is one percent of one percent of a foot per second squared, while the gravitational effect exerted by the Earth is approx ten feet per second squared.

So when the moon is directly overhead, you are one hundred thousandth lighter than otherwise. Your scale probably isn’t sensitive enough to detect that.

Yes, but I doubt it’s measurable for the normal mass/weight of a human, and I’m certain a normal human won’t be able to detect the difference without some really accurate measuring device.

No.

You could use a calibrated spring-type scale; it would have a fault - it would show a slightly lower weight than is really there, since the weight of the spring itself would be less, but it should show the difference. That is, if you can make a spring-based scale that was accurate enough. I’m sure that actual measuring devices on that kind of scale (heh) don’t use simple springs - I’d imagine without good insulation/AC, the temperature differences alone would have a bigger effect than the attraction of the moon or sun.

Which would seem to indicate that a bigger effect would be caused by moving the scale up to the second floor of your house. (Still probably unmeasurable, even by the most sensitive scales.)

Wouldn’t that be 32 ft/sec[sup]2[/sup] ? (Or am I missing something here?)

No, you’re right. Ten metres per second squared is a quick and dirty approximation (9.81 is closer).

Bah, real men use pi^2 for approximating g.

I love these ‘moon’s gravity’ things. A couple of weeks ago I heard a guy on the radio saying that farmers won’t set fence posts during a full moon because the moon’s gravity will pull them right out of the ground!

And a supposedly respectable UK paper printed something on its health page about an alleged causal link between the full moon and attacks of gout. Tidal forces on the bloodstream, donchaknow. :smack:

You would also perceive less gravity when the moon was directly below your feet (on the opposite side of the Earth).

He didn’t elaborate why there would be a difference in the moon’s gravity between a full moon and a new moon, did he?

Our midwife told us the reason the maternity unit was full was due to a full moon, and that it was probably tidal action on amniotic fluid that caused everyone’s waters to break at the same time

Even assuming that you could measure the difference, wouldn’t the moon be pulling the Earth toward it at the same rate, thus canceling it out?

Floater, the guy didn’t explain why there would be a difference in gravity with a full moon, nor did he explain how the same gravity that would pull a fencepost out of the ground wouldn’t lift a tractor, too, lol.

Not entirely. You’re closer to the Moon than the Earth’s center of gravity is, so the forces won’t quite be equal. This is the basis of tides.

Isn’t it obvious that the new moon, being the opposite of full, is therefore empty and so must exert much lower gravitational force?