Gravity and Uniformed Circular motion

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Discussion Overview

The discussion revolves around the relationship between gravity and uniform circular motion, exploring whether gravity can be considered a form of uniform circular motion and how it relates to centripetal acceleration. Participants examine the nature of gravitational force and its role in orbital mechanics, particularly in the context of satellites and their orbits.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if gravity can be classified as uniform circular motion, noting a lack of definitive statements in their readings.
  • Another participant clarifies that gravity is a force and not a motion, explaining that uniform circular motion requires a net centripetal force, which gravity can provide in specific cases like satellites in orbit.
  • A follow-up question arises regarding whether gravity can be considered a form of centripetal acceleration, with a distinction made between the force of gravity and the acceleration due to gravity.
  • It is noted that only in certain scenarios, such as a satellite in a circular orbit, does the acceleration due to gravity act as centripetal acceleration, while emphasizing that not all uniform circular motion is related to gravity.
  • Discussion includes the conditions under which a satellite maintains a circular orbit, highlighting the relationship between gravitational force and centripetal force, as well as the nature of elliptical orbits.
  • One participant introduces an analogy comparing gravity to electric charges, suggesting that the force lines of gravity can be visualized similarly, though this analogy is met with skepticism by others.
  • Concerns are raised about the appropriateness of using electric force analogies to explain gravitational concepts, with some participants arguing that it may lead to confusion.

Areas of Agreement / Disagreement

Participants express differing views on whether gravity can be categorized as uniform circular motion, with some supporting the idea under specific conditions while others argue against it. The discussion remains unresolved, with multiple competing perspectives on the relationship between gravity, centripetal acceleration, and orbital mechanics.

Contextual Notes

The discussion highlights ambiguities in the definitions of gravity and centripetal acceleration, as well as the conditions necessary for uniform circular motion. There is also a lack of consensus on the appropriateness of using analogies from electric forces to describe gravitational interactions.

am_knightmare
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Is gravity a Uniformed Circular motion? I had this question for a while and i googled searched it but no results, I also did the readings which I do think it is. But in the readings , I never read the statement that says gravity is a form of uniformed circular motion. Can anyone explain why or why not it is or isn't? Thanks.
 
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am_knightmare said:
Is gravity a Uniformed Circular motion?
Gravity is a force, not a motion.

To have uniform circular motion, you need a net centripetal force. In certain cases, gravity can provide that force, such as a satellite in a circular orbit about a planet.
 
Thanks for the reply. another question would be, gravity is a form of centripetal acceleration ? since they have the same units.
 
am_knightmare said:
Thanks for the reply. another question would be, gravity is a form of centripetal acceleration ? since they have the same units.
The term 'gravity' is a bit ambiguous. Do you mean the force of gravity? Or the acceleration due to gravity? Those are different, but related, things.

In any case, only in special cases, such as that satellite in circular orbit about a planet, would the acceleration due to gravity happen to be a centripetal acceleration.

Anything executing uniform circular motion is undergoing a centripetal acceleration, so there must be a net centripetal force acting. It may or may not have anything to do with gravity.
 
Thanks a lot, that was a good explanation.
 
Satellite orbits: Is this what the OP is basically about?

There is one particular speed for a satellite to travel that will cause its orbit to be exactly circular. This will be when the centripetal force is exactly equal to the gravitational force and it is moving at right angles to a radius. If you take a satellite which satisfies these conditions and give it a change in speed (boost or braking), or direction, it will no longer follow a circular orbit but an elliptical one. The gravitational force varies, depending on their orbital distance (inverse square law) and this is the only 'force law' that will lead to a stable, elliptical orbit afaik.
Most (all) orbits of planets, moons, satellites are, in fact, elliptical and not perfect circles. Sometimes they are far away and move slower and at other times they are closer and moving faster. But they do not 'fall out' of orbit nor do they escape because their total energy (Gravitational Potential plus Kinetic) remains the same.
 
Also, think of gravity like the picture of a negative charge. All the lines of force point inwards to a central point if the only body in the example is the body causing the gravity. At every distance, the force is the same, but decreases slowly as you move farther and farther away. This picture changes when you introduce another body. It is much like positive and negative charges in the way the force interacts.
 
Is it really such a good idea to bring in a totally different force (electric) when the forces, lines and fields in gravity can be pictured in just the same way?
 
Merely trying to explain the idea using a force simpler than gravity.
 
  • #10
Simpler?
You're lucky if you find it so.
 
  • #11
 
  • #12
That diagram is fine on its own but, on that link, it is followed by a whole set of diagrams, which involve numbers of opposite and like charges. Which of those would you relate to gravity and which could you not? If anything, you'd need to choose only the diagrams which involve like charges - but in those, the forces are repulsive.
If someone looks at that link and thinks they can learn about gravity, they may emerge worse off than before. That was my worry.
 

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