Here's a challenge: Prove that when a solid disc is set sliding at some speed on a horizontal surface with friction and also is given an arbitrary rotation (set spinning) , both motions will cease simultaneously. In other words, prove that you will never find that the disc is still translating while the rotation already stopped or that the disc stops translating but after that is still rotating for a while.
trueprober
Favorite Answer
Hello Dr Zorro, I think this type of motion is equivalent to a spiral motion on a frictional surface. So simultaneously both the motions would stop.
Dr. Zorro
Trueprober: interesting thought, but it isn't quite convincing though. You really have to write the equations of motion and play around with those to prove the result. At least that's how I did it. But maybe there is a compelling (topo)logical answer as well, so keep thinking about this problem 😄
eng.
hello Dr. Zorro,
Can you please give me your email adress??
Thank you