Centripetal Force: Why Don't Planets Fall from Sun?

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Discussion Overview

The discussion revolves around the concept of centripetal force and why planets do not fall into the Sun. Participants explore analogies involving spinning objects and gravitational forces, examining the differences between these scenarios and the dynamics of planetary motion.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant compares the motion of planets to a cup being spun on a thread, questioning why the Sun does not need to "wobble" to keep the planets in orbit.
  • Another participant suggests that the tension in the thread is analogous to the gravitational pull of the Sun, while also mentioning that the Earth is moving at a constant speed and may be slowing down.
  • There is a recognition that air resistance affects the spinning of the cup, implying that in the vacuum of space, the cup would continue spinning without additional force.
  • A later reply emphasizes that the Sun's gravitational attraction is responsible for keeping the planets in place, contrasting it with the direct force applied to the cup by the thread.
  • Participants discuss the distinction between centripetal and centrifugal forces, with one noting that the forces acting on the cup are not due to gravity but rather the tension in the string.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of centripetal force and gravitational attraction, with no consensus reached on the analogies presented or the implications for understanding planetary motion.

Contextual Notes

Some participants express uncertainty about their understanding of the concepts, indicating a lack of formal education on the topic. There are also references to assumptions about forces acting on the cup and the effects of air resistance, which remain unresolved.

Who May Find This Useful

This discussion may be of interest to students learning about gravitational forces, centripetal motion, and the dynamics of planetary systems.

Quincy
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Suppose if you're spinning a thread by your finger that has a cup attached to it at the other end. You would need to keep wobbling your finger or the cup would stop spinning, right? Then why doesn't the Sun wobble to keep the planets spinning around it? Or does the cup stop spinning because of the downward gravitation force?
 
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Quincy said:
Suppose if you're spinning a thread by your finger that has a cup attached to it at the other end. You would need to keep wobbling your finger or the cup would stop spinning, right? Then why doesn't the Sun wobble to keep the planets spinning around it? Or does the cup stop spinning because of the downward gravitation force?


I still haven't finished high school so i might be wrong, so here goes :) ...

when you wobble your fingers, i think you might be applying the tension which acts as the centripetal. The tension would be equivalent to the gravitational pull of the sun towards the earth. In addition to that, the Earth is moving at a constant speed (though i think its slowing down?), While the cup face frictional forces like air resistance, so tangentially its decreasing some of the force you apply by your fingers, most proabably also causes some sort of tangential acceleration too.

Please if I'm wrong correct me, I will be having a quiz on this topic, which me luck :D

thanks,
 
Abdou said:
I still haven't finished high school

lol same here.

I forgot about air resistance; so I guess if you spin the cup in outer space, it will keep on spinning without having to wobble your finger.
 
The sun keeps the planets in place via gravitational attraction...the curvature of spacetime.

Your finger has no gravitational attraction to a cup...at least it's negligible...you move the cup via the string via directly applied force...you apply centrifugal force to the cup; centripetal force holds in for accelerating from you...not gravity...
 

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