Torque

Torque is a measure of how much force acting on an object causes that object to rotate. Torque about a point is a concept that denotes the tendency of force to turn or rotate an object in motion. This tendency is measured in general about a point. It is also termed as "moment of force". The torque in angular motion corresponds to force in translation. Torque is rotational force or the ability to overcome resistance to rotation. It is the cross product of force and radius. Torque is the amount of force applied tangentially to a circle .Torque has dimensions of force time's distance. The unit Newton meter (N*m) or the unit joule per radian .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. 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. A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum is its torque. A force of three Newton's applied two meters from the fulcrum, for example, exerts the same torque as a force of one Newton applied six meters from the fulcrum.