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I'm suspicious of this ball and string. If you cut the ball off, a physical string would still be taut.
Sort of. The point of a ball on the end of a string is that you can simplify the system and ignore the elasticity of a string, air resistance, etc. It's a point mass (the ball) on the end of a light inelastic string.
If you take away the ball then you have to come up with something that is the mass at the end of the string. The natural thing would be to consider splitting the string into two halves, and that the half furthest from the anchor point is a mass that replaces the ball for the sake of the setup.
Greenbank-
Sort of. The point of a ball on the end of a string is that you can simplify the system and ignore the elasticity of a string, air resistance, etc. It's a point mass (the ball) on the end of a light inelastic string.
But if I recall my ancient physics A level, normally model strings are massless and transmit forces between masses. This model doesn't seem to follow this convention by having a string with mass - what's the physicist's equivalent to a programmer's 'code smell'?
If you take away the ball then you have to come up with something that is the mass at the end of the string. The natural thing would be to consider splitting the string into two halves
This seems to complicate rather than simplify and again- why not model the whole thing as a single rotating body? I think it's wrong to think of an 'anchor point' in the inertial frame, it's just the centre of rotation of the system, where there are no resultant forces - can't be, as it's not moving.
The natural thing would be to consider splitting the string into two halves, and that the half furthest from the anchor point is a mass that replaces the ball for the sake of the setup.
I suspect this is a trap - as soon as you start focusing on components of the system, you are constructing a non-inertial frame.
chez_jay
I'm suspicious of this ball and string. If you cut the ball off, a physical string would still be taut. So I don't think we need the ball to demonstrate the behaviour, and so we can simplify the model to a single rotating rigid body, with mass and thus inertia. So the two bodies bit doesn't seem to be relevant.
I don't see any room for a centrifugal force in this model, it's just inertia. There doesn't need to be balanced forces at any point on the body, as it's all rotating and thus accelerating.
Edit: Going back to the original ball and string, I suspect that visualising a force transmitted through the string to the ball is implicitly constructing a non-inertial reference frame.