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center o bass
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I have just studied a problem regarding a yoyo being pulled along a horzontal plane and where the task is to find which way the frictionforce from the ground on the yoyo is acting. I have seen the solution to it, but I find it confusing and would therefore like to ask some questions about it.
Allright.. the situation is as shown in (3): http://www.uio.no/studier/emner/matnat/fys/FYS-MEK1110/v10/eks/eksoppg02.pdf (it's in norwegian but you can see a sketch of the scenario).
As I said, I have seen the solution. There they are using N2L, N2L for rotation and the kinematic condition we have for rolling motion where the relative velocity between the ground and the point in contact with the ground is zero.
To start with they just assume that the friction force acts backwards and from there on finds an expression for the frictionforce and thereby a condition on the relation between the inner and the outer radius which shows what way the frictionforce is really acting.
The problem I have with this solution is that they use the rolling condition! When one uses this condition isn't that equivalent to saying that we have rolling motion troughout the whole motion. And if we have rolling motion must not the frictionforce allways act forward regardless of the relation between the radii?
Allright.. the situation is as shown in (3): http://www.uio.no/studier/emner/matnat/fys/FYS-MEK1110/v10/eks/eksoppg02.pdf (it's in norwegian but you can see a sketch of the scenario).
As I said, I have seen the solution. There they are using N2L, N2L for rotation and the kinematic condition we have for rolling motion where the relative velocity between the ground and the point in contact with the ground is zero.
To start with they just assume that the friction force acts backwards and from there on finds an expression for the frictionforce and thereby a condition on the relation between the inner and the outer radius which shows what way the frictionforce is really acting.
The problem I have with this solution is that they use the rolling condition! When one uses this condition isn't that equivalent to saying that we have rolling motion troughout the whole motion. And if we have rolling motion must not the frictionforce allways act forward regardless of the relation between the radii?
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