Torque:

Torque is the measure of force acting on an object which causes that object to rotate. Torque about a point is a concept which denotes the tendency of force to turn or rotate an object in the motion. This tendency is measured about a point in general. It is also called as "moment of force". The torque in an angular motion corresponds to force in translation. Torque is rotational force or ability to overcome the resistance to rotation. It is the cross product of radius and force. The torque is the amount of force applied tangentially to the circle .Torque has dimensions of force time's distance. The unit Newton meter or the unit joule per radian .The object rotates about its axis, which we will call the pivot point, and will be labeled as 'O'. We represent the force by 'F'. The distance from the pivot point to the point where the force is acting is called as moment arm, and can be denoted by 'r'. This distance, 'r', is also a vector, and points from the axis of rotation to the point where the force is acting. By using the right hand rule, we can find direction of the torque vector. If we put our fingers in direction of r, and curl them to direction of the F, then thumb points in direction of the torque vector.

Suppose pushing a door to open it. The force of your push (F) makes the door to rotate about its hinges (pivot point, O). How hard you are required to push depends on the distance you are from the hinges (r) (and other things, but let's ignore them now). The closer you are to the hinges (that is the smaller r is), the harder it is to push. This is what happens when you try to push open a door on wrong side. The torque you applied on the door is less, than it would have been had you pushed the correct side. A force applied at the right angle to a lever multiplied by the distance of it from the lever's fulcrum is its torque. A force of 3 Newton's applied 2 meters from the fulcrum, for instance, exerts the same torque as a force of 1 Newton applied 6 meters from the fulcrum.