Oscillations - A puzzling demonstration

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Discussion Overview

The discussion revolves around the puzzling demonstration of oscillations observed in a lecture from MIT's Physics 8.01 course, specifically focusing on the behavior of a ball rolling on a curved track compared to an air car on a larger track. Participants explore the reasons behind the differences in time periods of oscillation for the two objects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why the ball on the smaller radius track has a larger time period than the red object on the larger track.
  • Another participant suggests that the difference may stem from the ball being in contact with the track, implying a distinction from a pendulum's motion.
  • A later reply emphasizes that the ball's rolling introduces additional angular momentum, which may affect its motion compared to the air car, which has zero angular momentum.
  • One participant proposes a relationship between angular velocity and radius, stating that as the radius decreases, angular velocity should increase, leading to a decrease in time period, and questions why the time period actually increased.
  • Another participant reiterates that the increase in time period is due to the ball having additional angular momentum, resulting in less linear momentum compared to if it were sliding down the track.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics involved in the oscillations, particularly regarding the roles of angular momentum and linear momentum. The discussion remains unresolved, with multiple competing explanations presented.

Contextual Notes

Participants reference specific physical relationships, such as angular velocity and time period, but do not reach a consensus on the implications of these relationships in the context of the demonstration.

Elixer
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I watched MIT OCW PHYSICS 8.01 lectures, and in lecture no.13, i saw a puzzling demonstration. Link :http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/detail/embed13.htm"

I don't understand, what can be the reason for the oscillations of ball on the track with the smaller radius to have a larger time period than the oscillations of the red object on the larger track? :confused:Please explain.

Thank you.
Elixer
 
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Cute.

Well, to repeat the question that was asked, but in a more leading way:
How is a ball on a curved track not like a pendulum?
 
I think the answer lies somewhere in the fact that the metal ball rolling on a track is actually in contact with the track, but I'd have to think it through some more. This is a very cool demonstration though.
 
What are the balls doing on the track that is different from a pendulum?

Edit: I have now actually watched the demo, I'll rephrase my question.

What is the ball doing on the track that the air car is not?
 
Last edited:
Good lecture - great little demo.
I wonder how many of the students came up with the answer "in the shower".
 
Aha! I feel foolish now :frown:. The answer is because the ball is rolling and has an additional angular momentum, while the air car has zero angular momentum. I should have caught that right away, but i was sort of right in the sense that the ball rolls because it's in contact with the track.
 
So the ball has an angular momentum as well.
But , consider the following

The ball on the circular track has an angular velocity
w = squareroot(g/R)[where R = radius of circular path ,g = acceleration due to Earth's gravity]
So, as the radius of the path the ball travels decreases, w should increase hence time period should decrease, why did T increase?
 
T increased because the ball has an additional angular momentum, and thus less linear momentum than if the ball had slid down the track without rolling.
 

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