Question about gravity's effect on moving bodies

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Discussion Overview

The discussion revolves around the nature of gravity and its interaction with moving bodies, particularly whether gravity can be analogized to a friction-like force that causes objects to lose energy. Participants explore this concept through a metaphor involving a stretchy fabric and a marble, questioning the implications of such an analogy.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant proposes an analogy of gravity as a stretchy fabric that causes a marble to lose energy due to friction.
  • Another participant argues against the analogy, stating that if gravity caused friction, it would imply a preferred frame of reference where objects would eventually come to rest.
  • A different participant challenges the initial analogy, emphasizing that gravity is not like friction and questions the implications of energy loss in this context.
  • Concerns are raised about the conservation of energy, suggesting that if energy is lost to friction, it must be transferred somewhere, which complicates the analogy.
  • Questions are posed regarding the expected behavior of planets under the influence of gravity if it were analogous to friction, specifically whether they would spiral into the sun over time.

Areas of Agreement / Disagreement

Participants express differing views on the analogy of gravity as friction, with no consensus reached on the validity of this comparison or its implications for energy loss.

Contextual Notes

Participants highlight the need for a more complete understanding of energy transfer and conservation when discussing the effects of gravity, indicating that assumptions about energy loss may not align with established physical principles.

Veridian
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I have a question about gravity and the way it interacts with moving bodies. Let's say gravity was the surface of a very stretchy fabric. You take an object like a marble and roll it across an infinite plane of this fabric. The fabric causes the object to lose energy because of friction. My question is: does gravity work the same way? Does gravity cause objects to lose energy because of 'friction'?
 
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No. If gravity caused a sort of friction then you would have a preferred frame, the frame in which it eventually would come to rest.
 
Veridian said:
I have a question about gravity and the way it interacts with moving bodies. Let's say gravity was the surface of a very stretchy fabric.
There's your first problem- it's not!

You take an object like a marble and roll it across an infinite plane of this fabric. The fabric causes the object to lose energy because of friction. My question is: does gravity work the same way? Does gravity cause objects to lose energy because of 'friction'?
 
HallsofIvy said:
There's your first problem- it's not!
It helps to look at things in various ways, even if it's not always right.

Veridian said:
Does gravity cause objects to lose energy because of 'friction'?

When you say "lose energy" I assume you mean kinetic energy?

If this were the case, wouldn't you expect planets to spiral into the sun? Earth would have been getting closer and closer to the sun over it's lifetime.


The thing about energy lost to friction is that the energy goes somewhere (mostly to thermal energy).

Your picture is only half of a picture, you would need to imagine something for the energy to be transferred to (or else you're challenging conservation of energy).
 

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