Does Gravity Between Two Equal Mass Objects Cancel Out?

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Discussion Overview

The discussion centers on the gravitational interaction between two equal mass objects, specifically whether their gravitational forces cancel each other out when they are placed in proximity. The scenario is framed within a thought experiment involving two identical apples falling towards each other from antipodal points on Earth, considering the absence of atmospheric effects and other gravitational influences.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that if two identical apples fall towards each other from antipodal points, the acceleration of the Earth would be zero due to the symmetry of the situation.
  • Others argue that while the gravitational forces between the two apples exist, they do not "cancel out" in a way that negates the gravitational attraction; rather, both objects still exert a force on each other.
  • A participant questions the meaning of "ANTIPODIAN altitude" and seeks clarification on the concept, indicating a need for further explanation of the scenario.
  • One participant emphasizes that Galileo's demonstration was about the rate of fall of objects towards Earth, not about the interaction between two objects of equal mass.
  • There is a suggestion that the center of mass of the two-object system would not move, indicating a distinction between the forces acting on the individual objects and the system as a whole.

Areas of Agreement / Disagreement

Participants express differing views on whether the gravitational forces between the two equal mass objects cancel each other out. There is no consensus on the implications of the gravitational interaction in the proposed scenario.

Contextual Notes

Some participants highlight the need for clarity regarding terms and concepts, such as "ANTIPODIAN altitude," and there are unresolved questions about the implications of gravitational forces in the context of the thought experiment.

zarmewa
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Galileo was first to demonstrate that all objects fall at the same rate in the absence of an atmosphere. As it is said that the Earth and the Apple fall toward each other but apple looks a lot to falls to the Earth as compared to the falling of Earth toward the Apple which is so tiny to be detected.

Let's imagine Earth is a homogeneous sphere and two identical apples start falling simultaneously from same ANTIPODEAN altitude in the absence of all other gravitational attraction including atmosphere.

So what would be the direction of accelaration of earth?

If net accelaration of Earth is zero in aforementioned scenario then would gravity "g" of two equal spherical spheres/ planets cancel each other if placed on each other?
 
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zarmewa said:
Galileo was first to demonstrate that all objects fall at the same rate in the absence of an atmosphere. As it is said that the Earth and the Apple fall toward each other but apple looks a lot to falls to the Earth as compared to the falling of Earth toward the Apple which is so tiny to be detected.

Let's imagine Earth is a homogeneous sphere and two identical apples start falling simultaneously from same ANTIPODEAN altitude in the absence of all other gravitational attraction including atmosphere.

So what would be the direction of accelaration of earth?

If net accelaration of Earth is zero in aforementioned scenario then would gravity "g" of two equal spherical spheres/ planets cancel each other if placed on each other?

Two points that are antipodal to one another are connected by a straight line running through the centre of the Earth. China and Argentina are one example of antipodal points. So, if you would please explain what "ANTIPODIAN altitude" means it would help me understand what you are asking. Thank you. By the way, it is spelled "acceleration"
 
:frown:Let A and B are anitipodal points.

Assume

An apple is dropped from a height of h = 100 feet above ground level [point A]

An apple is dropped from a height of h = 100 feet above ground level [point B]
 
zarmewa said:
Galileo was first to demonstrate that all objects fall at the same rate in the absence of an atmosphere. As it is said that the Earth and the Apple fall toward each other but apple looks a lot to falls to the Earth as compared to the falling of Earth toward the Apple which is so tiny to be detected.

Galileo was not demonstrating that an apple falls toward the Earth at the same rate that the Earth falls toward an apple.

Galileo was demonstrating that two objects (both of insignificant mass compared to Earth), both falling toward Earth, fall at the same rate.

zarmewa said:
Let's imagine Earth is a homogeneous sphere and two identical apples start falling simultaneously from same ANTIPODEAN altitude in the absence of all other gravitational attraction including atmosphere.So what would be the direction of accelaration of earth?
Zero. What does this have to do with the first part of your post?

You are conflating two separate scenarios.

zarmewa said:
If net accelaration of Earth is zero in aforementioned scenario then would gravity "g" of two equal spherical spheres/ planets cancel each other if placed on each other?
What do you mean by "cancel each other out"? They are still pulled toward each other with a significant force.

Regardless of the mass of the two (or even three) objects, the centre of mass of the two (or three) body system will have an acceleration of zero (i.e. the CoM will not move). What does this have to do with Galileo's discovery?
 
Last edited:

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