Understanding Circular Motion: Notes and Explanation with Visual Examples

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Discussion Overview

The discussion revolves around understanding circular motion through various illustrative examples and mathematical considerations. Participants explore the dynamics of objects in circular motion, particularly focusing on the forces at play and the implications of different scenarios, such as friction and energy conservation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant shares notes on circular motion and seeks feedback on their understanding, particularly regarding the use of constant acceleration equations in estimating the motion of a marble in a can.
  • Another participant raises concerns about the complexity of the problem, noting that the centripetal force acts inward and does not directly counteract gravity, suggesting a tilt in the can's motion.
  • A different participant proposes alternative examples, such as a theme park ride and a roulette ball, to illustrate the concepts more effectively.
  • One participant discusses two scenarios regarding the interaction between the ball and the can: one where the interaction is frictionless, leading to free fall, and another where the ball rolls, affecting its downward acceleration.
  • There is a reiteration of the theme park ride example as a better illustration of circular motion dynamics compared to the initial can scenario.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of the initial example involving the can, with some agreeing that it is flawed and others suggesting alternative scenarios. The discussion remains unresolved regarding the best way to conceptualize and illustrate circular motion.

Contextual Notes

Participants highlight assumptions about friction and energy conservation, as well as the complexity of the forces involved in circular motion. There is no consensus on the best illustrative example or the implications of different interactions between the ball and the can.

a.mlw.walker
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THIS IS NOT HOMEWORK, IT IS FOR MY OWN UNDERSTANDING

I have written a few notes to myself on circular motion, if it is right, i think it will help others trying to understand it. Please can someone check the attached pdf.

Imagine having a marble, in a tin can, and you are shaking the can in circles, causing the marble to stay on the side. As you slow the tin, the marble will slow, and at some point fall to the bottom.

The pdf is trying to show the maths of this, if you know the first two times for revolution.

It assumes constant deceleration.

I'm not sure about my use of the constant acceleration equation to estimate how far round its last revolution (as it decelerates), the ball will get.

thanks
 

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a.mlw.walker said:
Imagine having a marble, in a tin can, and you are shaking the can in circles, causing the marble to stay on the side. As you slow the tin, the marble will slow, and at some point fall to the bottom.

I think this is a really hard problem, because the centripetal force of the can on the marble is acting inwards (it's a central force), and it doesn't act directly against gravity. What you're really doing is tilting the can as you're moving it, so that there's a slight upward vertical component of the normal force of the wall of the can on the marble.

It also just occurs to me that since the can is moving, it's not obvious that the marble's trajectory is a circle. Another question, is the marble sliding without friction, or is it rotating along?
 
Damn, you caught me out, I was trying to think of a simple illustration, but as i wrote it i also noticed it was flawed, and hoped nothing of it. Better example is one of those theme park rides where you all stand against the edge of the cylindrical cage, the cage starts spinning and then the floor drops away, leaving you stuck to the wall and not falling.

Another example is a roulette ball spinning in its track before it falls.

Do they help?
 
Assuming no losses in energy you have two cases.

If the interaction between ball and can is frictionless, the ball falls as if it were in free fall, it's forward and angular velocity have no affect on the vertical acceleration due to gravity.

If the interaction between ball and can involves no slippages, then the ball is rolling, and the ball will accelerate downwards at bit slower, because angular energy is increased as well as linear energy as the ball descends.
 
Lets forget the can now, and look at the other two examples i mentioned above, the can was a rubbish idea.
Better example is one of those theme park rides where you all stand against the edge of the cylindrical cage, the cage starts spinning and then the floor drops away, leaving you stuck to the wall and not falling.

Another example is a roulette ball spinning in its track before it falls.
 
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