3 ms·
From a layman’s perspective, if something spins, you need to apply a force to it to stop spinning, otherwise it will just keep spinning. Hence, conservation of
by kergonath 4y ago
From a layman’s perspective, if something spins, you need to apply a force to it to stop spinning, otherwise it will just keep spinning. Hence, conservation of angular momentum. If you change the mass distribution, it will spin faster or slower, just like ice skaters (this is probably the most striking example), but the angular momentum is still conserved, regardless their linear momentum. There is no fundamental difference between this and what happens at the atomic scale.
The not layman’s answer is Noether’s theorem: the invariance of the laws of physics after a rotation of the frame of reference implies conservation of angular momentum.
- andreareina 4y agoWhich implies that it's separate from linear momentum (the conservation of which is implied by invariance after linear translations).
- kergonath 4y agoIndeed!
- mrow84 4y agoYour layman’s answer still doesn’t quite do it for me - if you had two masses in space, joined together by a wire, and you span them around their combined centre of mass, angular momentum would remain conserved even if we wound the wire in or payed it out. If I cut the wire, though, wouldn’t the masses immediately shoot off (roughly) in whatever direction they were travelling at the time? That is my interpretation of the “everything seems linear” perspective colordrops offered - it seems like you only get the apparent rotation because of all the other forces holding things together. edit: I accept that the non-layman’s answer may hold, I just find the intuition a bit off.
- drdeca 4y agoAngular momentum would still be conserved when you cut the wire though? Also, couldn’t you just as well frame all the linear momentum in terms of angular momentum? ... hm, I guess one question is, how would we describe a world where one is conserved but not the other, and visa versa, So e.g. a physics invariant under rotation around each point but not under translations, or visa versa... Well, it seems like being invariant under rotation around any point, should maybe imply invariance under translations as well.. But, if we are talking about just rotations around a particular point, then a good example is a model of an atom where we consider the nucleus to be the fixed origin, and with the electrons to just be in a rotationally symmetric potential well, and in that model angular momentum is quite important, while linear momentum isn’t quite so important?