Torque and forces parallel vs perpendicular to the axis of rotation....

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Discussion Overview

The discussion centers on the concept of torque and the effects of forces that are parallel versus perpendicular to the axis of rotation. Participants explore the definitions of torque, the conditions under which forces produce torque, and the implications of different force components acting on a lever arm.

Discussion Character

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

Main Points Raised

  • Some participants question why forces parallel to the axis of rotation do not produce torque.
  • Definitions of torque are discussed, including the idea that it is the tendency of a force to rotate an object around an axis and the mathematical representation as the cross product of the distance vector and force.
  • Participants analyze a diagram to identify which force components (axial, tangential, and radial) can cause rotation about a specified axis.
  • Some participants assert that the radial force (Fr) does not produce torque because it is perpendicular to the axis of rotation, while others suggest that the axial force (Fa) can cause rotation but about a different axis.
  • There is a discussion about the tangential force (Ft) and its ability to cause rotation about the axis, with some participants agreeing on its effectiveness.
  • One participant explains that the torque produced by a force depends on the angle between the distance vector and the force vector, noting that if the angle is zero, the torque is zero.
  • There is a distinction made regarding the axis of rotation when considering the axial force (Fa), indicating it can produce rotation but not about the original axis discussed (A-A).

Areas of Agreement / Disagreement

Participants express differing views on the effects of various force components on torque, with no consensus reached on the specific conditions under which each force produces rotation. The discussion remains unresolved regarding the implications of axial forces and their relationship to torque.

Contextual Notes

Participants reference a diagram that is not provided, which may limit the clarity of their arguments. The discussion also involves assumptions about the definitions of torque and the geometry of the forces involved.

rashida564
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why force parallel to the axis of rotation do not make any torque.
 
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What is the usual definition of a torque ?
 
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is the tendency of force to rotate object around an axis .
 
or it's the cross product between the force and the distance vector .
 
rashida564 said:
why force parallel to the axis of rotation do not make any torque.

rashida564 said:
is the tendency of force to rotate object around an axis .

Can you answer your own question now ? How can a force acting parallel to an axis tend to cause rotation about that axis ?
 
it can't
 
but way .
 
Torque demo.jpg


In the diagram :

A-A is the axis
B-C is a lever arm at right angles to the axis
Fa , Ft and Fr are axial , tangential and radial force components acting on the end of the lever arm at point C .

Which of the force components could cause rotation of the lever arm about axis A-A and which could not ?
 
Last edited:
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i think Fr
 
  • #10
can anyone help me please
 
  • #11
rashida564 said:
i think Fr
No. Look at the diagram carefully.
 
  • #12
Fr don't make torque because it is perpendicular to axis of rotation.
Fa i think
 
  • #13
can anyone help me
 
  • #14
Ft wiil cause rotation about AA axis...
 
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  • #15
Correct . Can you explain in words now why Ft does produce rotation about A-A axis and why Fa and Fr do not ?
 
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  • #16
Look t=r×f...the anlge btween r and fr is sin0=0...so torque is zero...no question for rotation...
However fa will produce rotaion but the axis will be different...(an axis which is perpendicular to AA...BUT NOT ALONG AA)
 
  • #17
So fa will rotate the object
 
  • #18
Yes obviously fa will...but as i said corresponding rotation axis will be different
 

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