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

In summary, the conversation discusses the idea of a reactionless drive mechanism and whether it is possible to produce a net force in a specific direction by varying the center of mass of a rotating circle. However, the concept is not possible due to various reasons, including the conservation of energy. The conversation is concluded with the suggestion to explore the provided links for more information on why a reactionless drive cannot work.
  • #1
NotASmurf
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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?
 
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  • #2
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.
 
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  • #3
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
 
  • #4
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?
 
  • #5
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.
 
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1. What is net force from a varying speed non-uniform rotating wheel?

The net force from a varying speed non-uniform rotating wheel is the total force acting on the wheel in a specific direction. This force is a combination of the centrifugal force, which is the force pushing the object away from the center of rotation, and the centripetal force, which is the force pulling the object towards the center of rotation.

2. How is net force from a varying speed non-uniform rotating wheel calculated?

To calculate the net force from a varying speed non-uniform rotating wheel, you will need to know the mass of the object, the radius of rotation, and the angular velocity of the wheel. The formula for calculating net force is F = m * ω^2 * r, where m is the mass, ω is the angular velocity, and r is the radius of rotation.

3. What factors can affect the net force from a varying speed non-uniform rotating wheel?

The net force from a varying speed non-uniform rotating wheel can be affected by several factors, including the mass of the object, the radius of rotation, and the angular velocity of the wheel. Additionally, any external forces acting on the object, such as friction or air resistance, can also affect the net force.

4. How does the net force from a varying speed non-uniform rotating wheel change as the speed of the wheel changes?

The net force from a varying speed non-uniform rotating wheel will change as the speed of the wheel changes. As the speed increases, the centrifugal force will also increase, leading to a larger net force. Similarly, as the speed decreases, the centrifugal force will decrease, resulting in a smaller net force.

5. How can the net force from a varying speed non-uniform rotating wheel be used in practical applications?

The net force from a varying speed non-uniform rotating wheel has many practical applications. It is essential in understanding the motion and stability of objects, such as a spinning top or a rotating satellite. It is also crucial in designing and analyzing machinery, such as engines and turbines, that rely on rotational motion. In addition, the concept of net force can be applied in sports, such as figure skating or gymnastics, where rotation plays a significant role.

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