General Question

Sueanne_Tremendous's avatar

Moons' gravity?

Asked by Sueanne_Tremendous (11285points) October 29th, 2008

Call me lazy for not looking this up, but I would be interested in your comments. This question is inspired by Lovelocke’s earlier one about if the moon disappeared. since childhood I have understood that the moon’s gravitational pull effects the tides. But how is that so? Earth’s gravity is far stronger than that of the moon. I mean heck, the astronauts have to weigh themselves down when they are trompping around up there. How can the moon’s gravity have such an effect?

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7 Answers

tekn0lust's avatar

You really should research this yourself. You won’t be disappointed in what you find. Such as the fact that the moon is constantly “falling” toward earth.

Start with newton’s third law.

Harp's avatar

All of the bodies in our solar system have some tidal effect on Earth’s seas, but only the sun and moon have enough gravitational influence to produce a marked effect. Yes, the Earth’s gravitation exerts a far greater force on the water, but you can think of the gravitational pull of the sun and moon as slightly subtracting from the pull of the Earth on the side facing those bodies, while slightly augmenting the pull of the Earth on the opposite side.

The effect is very small. We only notice it in huge bodies of water, and even then the movement is of only a few feet, almost nothing relative to the volume of water.

deaddolly's avatar

good question…i’d rather hear it here than have to shuffle thru all the wordy explanations elsewhere.

asmonet's avatar

@tekn0lust: It’s actually moving away about 3.82 cm/year.

Some links you might all enjoy. Particularly, this one considering the source.

When dinosaurs roamed the earth it was double it’s size now in the night sky. How effing cool is that?

I’m a nerd.

tekn0lust's avatar

@asmonet: We are not talking about the same thing. I described orbital motion you are describing a change in the distance from earth to the moon.

http://en.wikipedia.org/wiki/Orbit#Understanding_orbits

asmonet's avatar

@tekn0lust: Ah, I was confused by your choice of words, thank you for the link, I’m sure it will be informative to a lot of people. My response would have perhaps been more tailored to someone who was using ‘falling’ outside of the quotes, I’m so used to having to explain simple science things to some of my friends it didn’t occur to me you might have other knowledge of your own, just a little misplaced explanation on my part. :)

crazyivan's avatar

I was going to make the same correction as @asmonet when I first read your post, but thanks for clarifying, tekn0lust.

You might be interested to learn (I’m talking to Sueanne here, I’m sure my fellow moon-nerds already know this) that there is a tidal force on land as well. It is nowhere near as pronounced, but land is pulled slightly upward by the moon’s gravity as well. There land tides move the earth’s crust from five to nine inches up and down through the day.

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