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

• rashida564
In summary, torque is the tendency of a force to rotate an object around an axis. When a force is parallel to the axis of rotation, it does not produce any torque. The usual definition of torque is the cross product between the force and the distance vector. In the given diagram, Fa and Fr do not cause rotation about the A-A axis because they are perpendicular to it. Ft, on the other hand, can cause rotation about the A-A axis because it is tangential to the lever arm at point C. Fa can still cause rotation, but around a different axis perpendicular to A-A.
rashida564
why force parallel to the axis of rotation do not make any torque.

What is the usual definition of a torque ?

rashida564
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 .

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:
soumobrata and rashida564
i think Fr

rashida564 said:
i think Fr
No. Look at the diagram carefully.

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

can anyone help me

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)

So fa will rotate the object

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

## 1. What is torque?

Torque is a measure of the turning or twisting force on an object. It is calculated by multiplying the force applied to an object by the distance from the applied force to the axis of rotation.

## 2. How is torque different from force?

Force is a push or pull on an object, while torque is a rotational force that causes an object to rotate about an axis. Force is measured in Newtons (N) while torque is measured in Newton-meters (Nm).

## 3. What is the relationship between torque and the axis of rotation?

The magnitude of torque is directly proportional to the distance from the axis of rotation. This means that the longer the distance from the axis, the greater the amount of torque exerted on an object.

## 4. How does the direction of force affect torque?

The direction of force in relation to the axis of rotation determines whether the torque is parallel or perpendicular. Force applied parallel to the axis of rotation will result in a larger torque, while force applied perpendicular to the axis will result in a smaller torque.

## 5. How do torque and forces parallel vs perpendicular to the axis of rotation affect rotational motion?

Torque and forces parallel to the axis of rotation cause an object to rotate, while forces perpendicular to the axis of rotation cause an object to move in a linear direction. This is because torque is responsible for creating rotational motion, while forces perpendicular to the axis do not contribute to this motion.

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