Tides and Moon Gravitational Force

[gianeshwar]

We know Moon creates tides on seas.Then why doesn't Moon pull loose stones or other objects lying loose on earth?

 

[A.T.]

We know Moon creates tides on seas.Then why doesn't Moon pull loose stones or other objects lying loose on earth?

It pulls the stone, and the surface under the stone almost equally. The gradient in Moon's gravity is less than the attraction of the stone by the Earth.

 

[gianeshwar]

Thanks AT.Why did you use the word gradient?

 

[xAxis]

Gradient is approximately the difference in gravitational field between two points. The stones are small objects so the moons gravity has the same effect on the whole stone, unlike the ocean. The pull on the ocean "under" the moon is bigger than the pull on the ocean on the opposite side of the earth

 

[sophiecentaur]

The difference between small stones on land and small bits of water, in the sea, is that the stones are held back from moving by friction but the static friction in water is very low - so it can move. Try to make a pile of water and then a pile of stones - you will see what I'm getting at.