Torque and couple

Torque

By ka cheung chan


  When we open a door, there is the force asserted tangent to the radius (distance from the door's hinge axis). That rotating effect or action is called torque. Torque is the cross product of the force and the radius.

According to the cross product's rule, rotating anti-clockwise results positive torque value while clockwise has negative value.
In order to increase the torque, either can one increase the radius or force.

Couple

Imagine a steering wheel, two equal but reverse force A&B acting both sides on a centre point. So