Timeline for Will two bodies initially connected to and revolving around each other, start spinning when disconnected?
Current License: CC BY-SA 4.0
13 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 23, 2021 at 5:49 | comment | added | Al Brown | @Mauricio This is interesting... Im here reading your comments and realize youre describing exactly what I happened to do in my answer to the question, a case where it’s not rotating as it revolves. | |
| Aug 22, 2021 at 16:24 | comment | added | Mark H | @AlBrown See my comment above. The string provides torque when the system is initially set to spinning before the string is cut. | |
| Aug 22, 2021 at 16:22 | history | edited | Mark H | CC BY-SA 4.0 |
added 114 characters in body
|
| Aug 22, 2021 at 16:21 | comment | added | Mark H | @uk-ny If the body-string system is rotating at a constant rotational velocity prior to cutting, then the torque on the system is zero since nothing is gaining or losing rotational velocity. Cutting the string just reduces the string tension to zero, so there can't be any torque here because the force applied to the bodies drops to zero. There is only torque when accelerating the body-string system from rest. | |
| Aug 22, 2021 at 16:16 | history | edited | Mark H | CC BY-SA 4.0 |
added 359 characters in body
|
| Aug 22, 2021 at 15:56 | comment | added | uk-ny | For your first argument, why is it obvious that the string applies no torque, when seen from the point of view relative to the center of the body? For your second argument, see my edited question. | |
| Aug 22, 2021 at 15:38 | comment | added | Mark H | @uk-ny The string only applies torque to the bodies during the initial rotational acceleration to get the bodies spinning on the string, in other words, when your problem is being set up from a state where everything is at rest. | |
| Aug 22, 2021 at 15:30 | comment | added | uk-ny | Indeed, the bodies are spinning before the string is cut. But I am not sure that this spinning is not because they are connected by the string. In your terms, this is exactly my question - does the string apply torque to the bodies? | |
| Aug 22, 2021 at 15:26 | comment | added | Mark H | @Mauricio Not necessarily. If the string is only connected at one point, then the top will rotate until its center of mass is aligned with the string. Even if the connection point is at the center of mass, then the top will rotate if the axis isn't a 1D line. I could imagine a multipoint connection rigging with slip rings that would allow for spinning without the top rotating, but that goes rather far beyond the generic situation described by the OP. In any case, cutting the string still doesn't change the rotational motion of the bodies about their own centers of mass. | |
| Aug 22, 2021 at 15:14 | comment | added | Mauricio | Yeah, I guess the result in that case is different and should be acknowledged. | |
| Aug 22, 2021 at 15:13 | comment | added | Mark H | @Mauricio Are you thinking of something like the string being connected to the axis of a toy top? | |
| Aug 22, 2021 at 15:05 | comment | added | Mauricio | What if the string was initially connected to some principal axis so that the objects did not rotate before the string was cut? | |
| Aug 22, 2021 at 14:48 | history | answered | Mark H | CC BY-SA 4.0 |