Torque & Joules: Fact or Fiction?

  • Context: Undergrad 
  • Thread starter Thread starter Entanglement
  • Start date Start date
  • Tags Tags
    Joules Torque
Click For Summary

Discussion Overview

The discussion revolves around the relationship between torque and energy, specifically the units used to measure them, and the conceptual differences between torque and energy in the context of physics. Participants explore the definitions, units, and implications of measuring torque in Joules versus Newton-meters, as well as the application of these concepts in various scenarios, including linear and rotational motion.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants express doubt about the claim that torque can be measured in Joules, suggesting it is nonsensical and typically measured in Newton-meters (N-m).
  • Others argue that while the units of torque (N-m) and energy (J) are equivalent, their definitions and contexts of use are different.
  • There is a discussion about how energy is defined as the product of force and displacement, while torque involves the displacement between forces, leading to confusion over the term "displacement."
  • Some participants assert that torque does not require two forces, while others challenge this by referencing the concept of a couple in mechanics.
  • A question is raised about how work done by a torque is calculated, particularly in non-linear motion, prompting discussions about angular displacement and the relationship between linear and angular motion.
  • Participants reference external sources, such as Wikipedia, to clarify definitions and units, but there is no consensus on the interpretation of these sources.
  • Some participants note that torque can be misleadingly measured in Joules, emphasizing the importance of understanding the context in which these terms are used.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether torque should be measured in Joules or Newton-meters, and there are competing views on the definitions and implications of torque and energy. The discussion remains unresolved regarding the appropriate context for using these units.

Contextual Notes

Participants express uncertainty about the definitions of displacement in the context of torque and energy, and there are unresolved questions about the application of these concepts in rotational mechanics versus linear mechanics.

Entanglement
Messages
438
Reaction score
13
Wikipedia says that the unit of magnetic dipole moments is calculated by Joule/B that means that the torque is measured by joules
I really doubt that, it seems non sense.
 
Physics news on Phys.org
ElmorshedyDr said:
Wikipedia says that the unit of magnetic dipole moments is calculated by Joule/B that means that the torque is measured by joules
I really doubt that, it seems non sense.
Torque has units of Force*distance. Usually expressed as N-m, but equivalent to Joules though I do not recommend that usage. (Usually Joule is reserved for energy, not torque!)
 
Doc Al said:
But equivalent to Joules though!
How is that ?
 
Energy equals the product of the force and the displacement along which the force is done

And the torque is the product of the force and displacement between the two forces, the concept of displacement isn't the same in both cases
 
Last edited:
ElmorshedyDr said:
How is that ?
1 N-m = 1 J
 
ElmorshedyDr said:
Energy equals the product of force and the displacement

And torque is product of force and displacement between the two forces the " d " isn't the same in both cases
We are talking about units, not about the definitions of torque and energy. (That's why energy is Joules while torque is in N-m, despite the fact the units are equivalent.)
 
The units are are the same but their definitions are different
 
ElmorshedyDr said:
The units are are the same but their definitions are different
Right. (For example, one is a vector while the other is a scalar.)
 
  • #10
But I think that it's totally wrong to say that torque is measured by joules not just "unrecommended"
 
  • #11
Thanks jersey :smile:
 
  • #12
jersey?
 
  • #13
ElmorshedyDr said:
Wikipedia says that the unit of magnetic dipole moments is calculated by Joule/B that means that the torque is measured by joules
I really doubt that, it seems non sense.
I'm not seeing that (I'm seeing n-m), can you link and quote it please.
 
  • #15
  • #17
ImageUploadedByPhysics Forums1398188452.967609.jpg
 
  • #18
However, how is work done by a torque calculated ??

I know that work is calculated by f.d
I'm unable to apply that on non linear motion
 
  • #19
What is the equivalent of "distance" if something rotates instead of moving along a line?
 
  • #20
jtbell said:
What is the equivalent of "distance" if something rotates instead of moving along a line?

Angular displacement i.e. Radians

KE_{angular} = \frac{1}{2}I\omega ^2
 
Last edited:
  • #21
ElmorshedyDr said:
However, how is work done by a torque calculated ??

I know that work is calculated by f.d
I'm unable to apply that on non linear motion

Linear motion:
##W = \int_{a}^{b}\vec{F} (dot)d\vec{r}##
Angular motion:
##W = \int_{a}^{b}\vec{T}(dot)d\vec{\theta}##
 
Last edited:
  • #22
Oh wait, you were leading them on... @jtBell consider them edited
 
  • #23
Torque.theta ??

Theta is radian ?

Can you tell me the proof of that law??
 
  • #24
jtbell said:
What is the equivalent of "distance" if something rotates instead of moving along a line?
Shouldn't it be radian.radius ??
 
  • #25
ElmorshedyDr said:
Torque.theta ??

Theta is radian ?

Can you tell me the proof of that law??

Convert the linear work done by a tangential force along the circumference to torque the force produces around the center and angle the point of attack travels.
 
  • #26
This point was raised as a short question in an A level physics paper of years ago:

Torque can be measured in Joules but it is usually considered misleading to do so. Explain why? (I don't remember the exact wording)
 
  • #27
Dadface said:
This point was raised as a short question in an A level physics paper of years ago:
Torque can be measured in Joules but it is usually considered misleading to do so. Explain why? (I don't remember the exact wording)
Because the definition of d is different in case of torque and energy

Torque = f.d
Where d is the displacement between the two forces

Energy = f.d
Where d is the displacement along which the force is done
 
  • #28
ElmorshedyDr said:
Torque = f.d
Where d is the displacement between the two forces
Torque doesn't require two forces.
 
  • #29
A.T. said:
Torque doesn't require two forces.
Even if it is a rotating coil ??
 
  • #30
ElmorshedyDr said:
Even if it is a rotating coil ??
There is only one force in the definition of torque. So what "two forces" are you taking about?
 

Similar threads

Undergrad I'm calculating more energy out than I put in
  • · Replies 138 ·
5
Replies
138
Views
9K
Undergrad How to quantify gyroscopic precession torque?
  • · Replies 49 ·
2
Replies
49
Views
5K
Undergrad What is the Purpose of Torque?
  • · Replies 7 ·
Replies
7
Views
3K
Just looking for confirmation for a torque calculation
  • · Replies 60 ·
3
Replies
60
Views
4K
Undergrad Conservation of angular momentum during collisions
  • · Replies 3 ·
Replies
3
Views
3K
Graduate Torque and Moment of Inertia of a Lever Arm
  • · Replies 2 ·
Replies
2
Views
3K
Graduate What is the definition and significance of torque in physics?
  • · Replies 1 ·
Replies
1
Views
4K
High School The physics of flywheel launchers (like tennis ball shooters)
  • · Replies 60 ·
3
Replies
60
Views
7K
Undergrad Understanding Torque and Inertia: How Does it Affect Motion?
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad How Does Moment of Inertia Affect Motor Size Requirements?
  • · Replies 3 ·
Replies
3
Views
4K