Forces of gravitation of moon and earth + Newtons 3rd law

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Discussion Overview

The discussion revolves around the gravitational forces between the Earth and the Moon, specifically in the context of Newton's third law of motion. Participants explore the nature of these forces, questioning whether there are multiple pairs of forces involved and how the mass of each body influences the gravitational interaction.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that there are two pairs of gravitational forces between the Earth and the Moon, while another argues that there is only one pair of forces, specifically the gravitational force exerted by the Moon on the Earth and vice versa.
  • Some participants assert that the forces must be equal in magnitude and opposite in direction, in line with Newton's third law.
  • There is a question raised about the relative strength of the gravitational forces, with one participant expressing concern that the Moon's gravitational force on the Earth might be less than the Earth's gravitational force on the Moon due to the Moon's lower gravity.
  • Another participant emphasizes that the gravitational constant (G) is the same for any two objects, which is a point of confusion for some in the discussion.
  • The mass of the Earth compared to the Moon is noted as a factor influencing the gravitational force, with a participant suggesting that the force is based on the product of the masses of the two bodies.

Areas of Agreement / Disagreement

Participants generally disagree on the interpretation of the gravitational forces involved, with some asserting a single pair of forces and others suggesting multiple pairs. The discussion remains unresolved regarding the implications of mass and gravitational strength.

Contextual Notes

Participants express uncertainty about the application of Newton's law of gravitation and the implications of mass on gravitational force, indicating a need for further clarification on these concepts.

Abhishek Jain
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In relation to two objects with a gravitational field on them (i.e. a planet and its moon), would there be two pairs of partner forces (the force of gravity exerted from each object and the resulting partner force from each force of gravity)? For example with the Earth and moon:

1. Force of gravity exerted on the moon by the Earth = - Force exerted on Earth by moon
2. Force of gravity exerted on the Earth by the moon = - Force exerted on moon by earth

Or is the force of gravity exerted by the moon on Earth = - force of gravity exerted by the Earth on moon? My intuition would say my first answer is correct?
 
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Abhishek Jain said:
is the force of gravity exerted by the moon on Earth = - force of gravity exerted by the Earth on moon
This one.

The gravitational interaction between the Earth and moon results in one pair of forces.
 
They would have to be equal though? Isn't the force exerted by the moon's gravitation on the Earth going to be less than the force exerted by the Earth's gravitation on the moon (since gravity is less on the moon)?
 
Abhishek Jain said:
They would have to be equal though?
Equal magnitude, opposite direction. Yes.
Abhishek Jain said:
Isn't the force exerted by the moon's gravitation on the Earth going to be less than the force exerted by the Earth's gravitation on the moon (since gravity is less on the moon)?
Work it out. What does Newton's law of gravitation say?
 
Thanks! I didn't know that G is the same between any two objects. That was what was confusing me!
 
Abhishek Jain said:
They would have to be equal though? Isn't the force exerted by the moon's gravitation on the Earth going to be less than the force exerted by the Earth's gravitation on the moon (since gravity is less on the moon)?

But the Earth is more massive than the moon and the force is based on the product of the masses.
 

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