Why does a force parallel to the axis of rotation produce no torque?

[rashida564]

why force parallel to the axis of rotation do not make any torque.

 

[Nidum]

What is the usual definition of a torque ?

 

[rashida564]

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

 

[rashida564]

or it's the cross product between the force and the distance vector .

 

[Nidum]

why force parallel to the axis of rotation do not make any torque.

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 ?

 

[rashida564]

it can't

 

[rashida564]

but way .

 

[Nidum]

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 ?

 

[rashida564]

i think Fr

 

[rashida564]

can anyone help me please

 

[cnh1995]

i think Fr

No. Look at the diagram carefully.

 

[rashida564]

Fr don't make torque because it is perpendicular to axis of rotation.
Fa i think

 

[rashida564]

can anyone help me

 

[soumobrata]

Ft wiil cause rotation about AA axis...

 

[Nidum]

Correct . Can you explain in words now why Ft does produce rotation about A-A axis and why Fa and Fr do not ?

 

[soumobrata]

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)

 

[rashida564]

So fa will rotate the object

 

[soumobrata]

Yes obviously fa will...but as i said corresponding rotation axis will be different