Tides and Moon Gravitational Force

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Discussion Overview

The discussion centers on the gravitational effects of the Moon, specifically regarding why it influences ocean tides but seemingly does not affect loose stones or objects on Earth in the same way. The scope includes conceptual reasoning about gravitational forces and their differential effects on various materials.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why the Moon's gravitational pull does not affect loose stones on Earth, despite its role in creating tides.
  • Another participant suggests that the Moon does exert a pull on stones, but the gradient of the Moon's gravity is less than the gravitational attraction of the Earth on those stones.
  • A subsequent reply clarifies the term "gradient" as the difference in gravitational field strength between two points, noting that the Moon's gravity affects the entire stone uniformly, unlike the varying effects on the ocean.
  • Another participant highlights the role of friction, arguing that stones are held in place by friction, while water can move more freely due to its low static friction.

Areas of Agreement / Disagreement

Participants express differing views on the effects of the Moon's gravity on stones versus water, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

The discussion does not fully address the assumptions regarding the scale of gravitational effects and the conditions under which different materials respond to gravitational forces.

gianeshwar
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We know Moon creates tides on seas.Then why doesn't Moon pull loose stones or other objects lying loose on earth?
 
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gianeshwar said:
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.
 
Thanks AT.Why did you use the word gradient?
 
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
 
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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.
 
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