Ball rolling on a larger ball on a surface

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    Ball Rolling Surface
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Discussion Overview

The discussion revolves around a physics problem involving a smaller ball rolling on a larger ball on a surface, specifically examining the time it takes for the smaller ball to reach the bottom under different conditions, including frictionless surfaces and the introduction of friction with a coefficient of 0.2. The scope includes theoretical reasoning and mathematical modeling.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant proposes to calculate the time it takes for the smaller ball to reach the bottom, given specific masses and radii, under the assumption of frictionless surfaces.
  • Another participant notes that without static friction, the balls will slip, questioning the initial conditions necessary for the problem.
  • Some participants express uncertainty about how to begin solving the problem, indicating a need for relevant equations and conserved quantities.
  • It is mentioned that if there is friction, both balls may roll, but the smaller ball will likely slip before falling off.
  • One participant emphasizes that the time for the motion is indeterminate without specifying an initial velocity or angle for the smaller ball.
  • A reference is made to a similar problem discussed in another thread, highlighting the complexity of determining the motion of the smaller ball.

Areas of Agreement / Disagreement

Participants express uncertainty and differing views on how to approach the problem, with no consensus on the initial conditions or the effects of friction. The discussion remains unresolved regarding the specific calculations and outcomes.

Contextual Notes

Participants note the indeterminate nature of the time calculation without specific initial conditions, and the complexity of the problem is acknowledged, particularly in relation to friction and motion dynamics.

theQM123
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I've just been wondering about this kind of problem. Let m be the mass of the smaller ball, and M be the mass of the larger ball. Assuming the ball does not slip and that the surfaces are frictionless, what is the time that it takes for the smaller ball to reach the bottom/floor if the the radii for the small and large ball are 2m and 10m respectively?

What does it become when there is friction with a coeffecient of 0.2?
 
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If there is no static friction the balls will slip.

What did you find out so far?
 
The thing is, I don't quite know where to start.
 
theQM123 said:
The thing is, I don't quite know where to start.

If there is no friction, then neither ball will roll and both will slide. If there is friction, then they may both roll, although the smaller ball will eventually slip before it falls off.

Also, the time for this motion is indeterminate unless you specify an initial velocity and/or angle for the small ball.

There is actually another post at the moment, where someone has posted a similar problem:

https://www.physicsforums.com/threa...f-a-rough-spherical-dome.808105/#post-5072564

There is a simpler problem, where the large ball is fixed and there is no friction. In that case, you have to work out how far the small ball slides before it falls off. Even that, however, is not that easy a problem. It too, was posted on here a while back.

And, for this problem too, the time is indeterminate.
 
theQM123 said:
The thing is, I don't quite know where to start.
With relevant equations, for example. With conserved quantities. With things you know, with things you want to know, ...
With an easier problem, as PeroK sugggested.

There are tons of possible ways to start even if you have no idea how to approach the problem as a whole.
 

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