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

AI Thread Summary
Forces acting parallel to the axis of rotation do not generate torque because torque is defined as the tendency of a force to cause rotation around an axis, which relies on the angle between the force vector and the distance vector. The discussion clarifies that only forces acting perpendicular to the axis, such as tangential forces, can produce torque, while axial and radial forces do not contribute to rotation about that axis. The torque equation, t = r × f, indicates that if the angle between the radius vector and the force is zero, the torque is zero. Forces parallel to the axis may cause rotation, but around a different axis that is not aligned with the original axis of rotation. Understanding these principles is crucial for analyzing rotational dynamics effectively.
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 ?
 
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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 becuase 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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