- #1
mklein
- 43
- 0
Dear forums
Hello. I teach physics, and whilst I think that my knowledge is fairly sound, once every now and I then I encounter something which baffles me like so...
In a simple demo of circular motion, a rubber bung is whirled around the head in a horizontal plane. If the bung is allowed to wrap around the finger APPARENTLY it should speed up.
However, if we consider the equation for centripetal force: F = MV^2/r
The mass is constant, and presumably the force remains fairly constant as I am providing that. The radius has decreased, so surely the velocity should also decrease to some extent to keep the fraction constant.
How do I resolve this please ! I am starting to think I should just take an early retirement !
Cheers
Matt
Hello. I teach physics, and whilst I think that my knowledge is fairly sound, once every now and I then I encounter something which baffles me like so...
In a simple demo of circular motion, a rubber bung is whirled around the head in a horizontal plane. If the bung is allowed to wrap around the finger APPARENTLY it should speed up.
However, if we consider the equation for centripetal force: F = MV^2/r
The mass is constant, and presumably the force remains fairly constant as I am providing that. The radius has decreased, so surely the velocity should also decrease to some extent to keep the fraction constant.
How do I resolve this please ! I am starting to think I should just take an early retirement !
Cheers
Matt