Torque

Let Us Learn About Torque

Torque is a measure of how much a force acting on an object causes that object to rotate. The object rotates about an axis, which we will call the pivot point, and will label 'O'. We will call the force 'F'. The distance from the pivot point to the point where the force acts is called the moment arm, and is denoted by 'r'. Note that this distance, 'r', is also a vector, and points from the axis of rotation to the point where the force acts. (Refer to Figure 1 for a pictoral representation of these definitions.)

Torque is defined as

In other words, torque is the cross product between the distance vector (the distance from the pivot point to the point where force is applied) and the force vector, 'a' being the angle between r and F.

Using the right hand rule, we can find the direction of the torque vector. If we put our fingers in the direction of r, and curl them to the direction of F, then the thumb points in the direction of the torque vector.

Imagine pushing a door to open it. The force of your push (F) causes the door to rotate about its hinges (the pivot point, O). How hard you need to push depends on the distance you are from the hinges (r) (and several other things, but let's ignore them now). The closer you are to the hinges (i.e. the smaller r is), the harder it is to push. This is what happens when you try to push open a door on the wrong side. The torque you created on the door is smaller than it would have been had you pushed the correct side (away from its hinges).

Note that the force applied, F, and the moment arm, r, are independent of the object. Furthermore, a force applied at the pivot point will cause no torque since the moment arm would be zero (r = 0).

Another way of expressing the above equation is that torque is the product of the magnitude of the force and the perpendicular distance from the force to the axis of rotation (i.e. the pivot point).

Let the force acting on an object be broken up into its tangential (Ftan) and radial (Frad) components the radial component of the force has no contribution to the torque because it passes through the pivot point. So, it is only the tangential component of the force which affects torque

There may be more than one force acting on an object, and each of these forces may act on different point on the object. Then, each force will cause a torque. The net torque is the sum of the individual torques.

Rotational Equilibrium is analogous to translational equilibrium, where the sum of the forces are equal to zero. In rotational equilibrium, the sum of the torques is equal to zero. In other words, there is no net torque on the object.

In physics, when an external force is applied on the body, the body gets tendency to rotate over an axis called torque.Torque is considered as a vector quantity over an axis of rotation. The multiplication of the force magnitude and the perpendicular distance of the line. Torque is mainly for change the state of rotation. The other name of torque is a moment of force.

Torque in Physics:

Torque in physics:

Consider an external force F is applied on a body. The body can rotate through the point O about an axis and the direction is perpendicular to the paper.

As in figure the distance of the force from the point O is ON=r.

Then the torque of physics can be written as,

r = F. r

Unit of torque:

newton x meter

• The torque value is positive when the rotation of a body is anticlockwise.

• The torque value is negative when the rotation of a body is clockwise.

Two facts about torque in physics:

• If the value of r=0 through O then the torque is also zero. In this case the rotation of body is not possible. That is if the line of force is zero then torque is zero. For example, the sun has a torque is zero and the gravitational force acts on the earth makes an earth to rotate the sun.
• If the line of force distance increases then torque is also increases. That is the increase value of r cause the increase of torque. In this case a small force is required for rotating a body.