Torque & Power: Understanding Angular Velocity

  • Context: Undergrad 
  • Thread starter Thread starter firavia
  • Start date Start date
  • Tags Tags
    Power Torque
Click For Summary

Discussion Overview

The discussion revolves around the relationship between torque, power, and angular velocity, particularly in the context of rotating systems. Participants explore how torque can exist in systems with constant angular velocity and the implications of this on the understanding of power and friction.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant questions how torque can be expressed as power divided by angular velocity, given that torque is also defined as the moment of inertia times the change in angular velocity over time.
  • Another participant introduces an analogy involving a block on a table to illustrate the concept of power in the presence of friction, suggesting that constant speed does not imply zero force due to opposing friction.
  • A participant seeks clarification on whether the torque on a rotating disk is due to the initial force that accelerated it before reaching a state of equilibrium.
  • Another participant emphasizes that the constant force applied to maintain motion against friction is not the same as the torque being zero at constant speed.
  • One participant argues that the relationship between torque and power is often misunderstood, suggesting that a rotating object at constant speed can still have non-zero torque due to input and output torques being equal.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between torque, power, and angular velocity, with no consensus reached on whether torque can exist in systems with constant angular velocity or how these concepts interrelate.

Contextual Notes

There are unresolved assumptions regarding the definitions of torque and power, particularly in the context of rotating systems and the effects of friction. The discussion highlights the complexity of these relationships without reaching definitive conclusions.

firavia
Messages
136
Reaction score
0
how can we say that torque is equal to power / angular velocity though we know that torque is equl to I x (change of angular velocity over time ).

and how can we relate torque to (angular velocity) , as we know that a rotating gear at constant angular velocity has no torque on it or bettter saying the sum of all torques on it are equal to zero, so how can we say that torque is equal to the power of the rotating gear over the constant angular velocity ? arent we contradicting ourselfs ?? how can a torque exist on a constant angular velocity rotating gear ? I am confused ??
 
Last edited:
Physics news on Phys.org
If you push with a force F a block on a table with friction such that the block moves at constant speed v, then the power you produce is Fv. So the conundrum here would be F=ma, but the block is not accelerating? The reason is that we have forgotten to take into account that there is friction. In the presence of friction, if you don't push, the block doesn't even move.
 
so u're saying that the torque calculated on the rotating disk is due the force that initialy rotated the disk ?? which means initially accelerated the disk before it reached its equilibriumed state (acceleration = 0) ? right ?
 
No, in the example P=Fv, I am giving the constant force (equal and opposite to the friction) you need to apply to keep the block moving at a constant speed.
 
firavia said:
how can we say that torque is equal to power / angular velocity though we know that torque is equl to I x (change of angular velocity over time ).
Why do you think these ideas are mutually exclusive? Try writing them in equation form and see if they make more sense.

One thing that may be confusing you - typically that first relationship is written the other way around: power equals torque times angular velocity.
and how can we relate torque to (angular velocity) , as we know that a rotating gear at constant angular velocity has no torque on it or bettter saying the sum of all torques on it are equal to zero, so how can we say that torque is equal to the power of the rotating gear over the constant angular velocity ?
arent we contradicting ourselfs ?? how can a torque exist on a constant angular velocity rotating gear ? I am confused ??
Saying that all torques sum to zero is different from saying that the torque at constant velocity is zero. It is not [necessarily] true to say a rotating object at constant speed has no torque on it: there may an input and an output torque that are equal. Power and energy work the same way.
 

Similar threads

High School What is physical significance of the direction of angular velocity?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Calculate acceleration from power/torque graphs
  • · Replies 17 ·
Replies
17
Views
1K
Undergrad Is energy really conserved?
  • · Replies 39 ·
2
Replies
39
Views
4K
Undergrad Is angular momentum perpendicular to fixed axis of rotation constant?
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Conservation of angular momentum in the iceskater example
  • · Replies 10 ·
Replies
10
Views
2K
High School The physics of flywheel launchers (like tennis ball shooters)
  • · Replies 60 ·
3
Replies
60
Views
7K
Undergrad Force & Torque: Acceleration, Power & Angular Velocity
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Effects of External Torques on the Angular Momentum of Asymmetric Bodies
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Increasing the output torque of a DC motor with gears
  • · Replies 16 ·
Replies
16
Views
4K
Undergrad Writing an equation for torque around an arbitrary point on a body
  • · Replies 6 ·
Replies
6
Views
1K