Net force from a varying speed non-uniform rotating wheel?

Click For Summary

Discussion Overview

The discussion revolves around the concept of net force in a non-uniform rotating wheel, particularly when the wheel's speed varies over time and its mass distribution is not uniform. Participants explore whether such conditions could lead to a net directional force and the implications for energy conservation.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that a rotating circle generates a centripetal acceleration (v^2/r) but argue that this does not result in a net directional force due to cancellation effects.
  • Others clarify that if the center of mass is not aligned with the rotation axis, a time-dependent net force is required for rotation around an off-center axis, but the average force over one complete rotation remains zero.
  • One participant suggests that the discussion may relate to concepts like Reactionless Drives, which are generally not accepted in mainstream physics.
  • Another participant expresses confusion regarding energy conservation in relation to the proposed mechanisms, questioning whether energy conservation could be violated if a net force is achieved.
  • A later reply emphasizes that the topic is not typically discussed in the forum, indicating a consensus against exploring such unconventional ideas.

Areas of Agreement / Disagreement

Participants express disagreement on the feasibility of achieving a net force through the proposed mechanisms, with some asserting that energy conservation principles would prevent such outcomes. The discussion remains unresolved regarding the validity of the initial claims and the implications for energy conservation.

Contextual Notes

Participants reference complex mathematical relationships and conservation laws, but the discussion does not resolve the assumptions or dependencies involved in these claims.

NotASmurf
Messages
150
Reaction score
2
If we have a circle rotating then a force v^2/r is produced but no net directional force exists as it cancels.
But if the wheel was not uniform in mass ie not rotating around its centre of mass AND the speed changes over time as a function of the "wheel"'s rotation angle could a net force be produced in a direction of choice? If not then could it be achieved by doing the above AND varying the centre of mass?
 
Physics news on Phys.org
NotASmurf said:
If we have a circle rotating then a force v^2/r is produced but no net directional force exists as it cancels.
That is not a force, it is an acceleration. More precisely, it is the magnitude of the acceleration of an object rotating with the disk at radius r.

If the center of mass is not at the rotation axis you need a time-dependent net force on the object to have it rotating around its off-center rotation axis, but integrated over one rotation the average force is zero.

Accelerating the system doesn't change anything, shifting masses around just makes the calculations more complicated, and overall momentum and energy are conserved exactly.
 
  • Like
Likes   Reactions: NotASmurf
NotASmurf said:
If we have a circle rotating then a force v^2/r is produced but no net directional force exists as it cancels.
But if the wheel was not uniform in mass ie not rotating around its centre of mass AND the speed changes over time as a function of the "wheel"'s rotation angle could a net force be produced in a direction of choice? If not then could it be achieved by doing the above AND varying the centre of mass?
It sounds like you are trying to discuss a Reactionless Drive mechanism, which along with PMMs and Over-Unity mechanisms, we do not take the time to discuss. Is that what you are asking about?

https://en.wikipedia.org/wiki/Reactionless_drive
 
I know this post seems stupid, only asking because our physics TA (in honours and spends too much of his clean energy optimization funding on rent) said that this was "an active area of research".

Oh, is the reason this isn't possible because (sorry for no latex, my keyboard is broken, on screen keyboard is effort and latex takes more typing):

e=.5mv^2, f=ma

f=m. ∂/∂t [2e/m]^0.5

for a net force we need:
Σf=0
to not be true.

thus
Σf≠0 ⇒ f≠[2]^0.5 * ∂/∂t * [m^-0.5 * e^0.5 * m] ⇒ 0 ≠ Σ(e^.5)(m^[-3/2]) ⇒Σe≠0

So if he was right energy wouldn't be conserved?
 
As I said, we don't waste time discussing such things here. Thread is closed.

EDIT / ADD:
NotASmurf said:
So if he was right energy wouldn't be conserved?
There are many reasons it cannot work, energy conservation could be one of them. Please follow the links in the Wikipedia article for more reasons it cannot work.
 
Last edited:
  • Like
Likes   Reactions: NotASmurf

Similar threads

  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 32 ·
2
Replies
32
Views
3K
Replies
2
Views
2K
  • · Replies 22 ·
Replies
22
Views
5K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 24 ·
Replies
24
Views
3K
  • · Replies 25 ·
Replies
25
Views
2K
  • · Replies 12 ·
Replies
12
Views
5K