The Angular Velocity in Belt Drives

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Discussion Overview

The discussion revolves around the behavior of angular velocity in belt drives, specifically examining the relationship between the angular velocities of driven and following pulleys, the role of torque, and the effects of friction. Participants explore theoretical aspects and potential misunderstandings regarding constant angular velocity and the influence of belt tension and friction.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that if the driven pulley rotates with constant angular velocity and the belt does not slip, then the relationship w1/w2=d2/d1 implies w2 should also be constant.
  • Another participant suggests that torque from the tensions in the tight and loose sides of the belt would prevent the following pulley from maintaining a constant angular velocity.
  • Some participants argue that torque is present only if there is friction, which would cancel out the torque from the belt.
  • There is a discussion about the effects of friction forces and press forces on the following pulley, with one participant claiming that only friction forces create torque.
  • Concerns are raised about how a following pulley can rotate at constant velocity despite the presence of torque due to friction from the belt.
  • Another participant points out that if friction between the shaft and pulley is negligible, then the friction from the belt should also be considered negligible.
  • One participant reminds others to consider the external torques acting on the two pulleys, which should equal the torques from the belt.

Areas of Agreement / Disagreement

Participants express differing views on the role of friction and torque in the operation of belt drives, indicating that multiple competing perspectives remain unresolved regarding the conditions under which the following pulley can maintain a constant angular velocity.

Contextual Notes

Participants discuss assumptions regarding friction and torque without reaching a consensus on the implications of these factors in the context of belt drives.

daigiaga1994
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Consider the belt drives, the driven pulley: diameter d1, angular velocity w1 and the follow pulley: diameter d2, angular velocity w2.

Assuming that the driven pulley rotate with a constant angular velocity and the belt does not slip on the pulleys, we have w1/w2=d2/d1, so w2 is constant( because w1 is constant).
But I think that the follow pulley will have a torque which is caused by the tensions in the tight and loose sides of the belt. Because of this torque, the follow pulley can't rotate with a constant angular velocity. This is opposite to the above statement ( w2 is constant).
Please explain this misunderstanding for me, thank you.
 
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You have torque (and a tight and loose side) only if the following pulley has friction, and this torque will exactly cancel the frictional torque.
 
mfb said:
You have torque (and a tight and loose side) only if the following pulley has friction, and this torque will exactly cancel the frictional torque.
But I think, the effect of the belt on the following pulley are the friction forces ( tangent to the pulley) and the press forces ( normal to the pulley). So only friction forces can create the torque on the pulley. That is my thought.
 
How is that in conflict with my previous post?
If the whole setup is frictionless, both sides will have the same tension. If there is friction, making the pulley slower than the belt or "trying" to slow down the pulley, then you get an accelerating torque from the belt and a braking torque from friction (probably close to the axle).
 
mfb said:
How is that in conflict with my previous post?
If the whole setup is frictionless, both sides will have the same tension. If there is friction, making the pulley slower than the belt or "trying" to slow down the pulley, then you get an accelerating torque from the belt and a braking torque from friction (probably close to the axle).
yeah, but I wonder that Why the following pulley can rotate with a constant velocity with a torque( due to friction exerted by the belt) ? ( In this case, assuming that the friction between shaft and pulley is negligible ).
Thank you.
 
daigiaga1994 said:
( In this case, assuming that the friction between shaft and pulley is negligible ).
If that is true, friction from the belt is negligible as well.
 
Hi.Daigiaga, sorry but you are forgotten the exterior torques over the two pullies which equals the torques of the belt
 

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