Moment of a force or Torque is the measure of an object's tendency to rotate about some point O.
Moment of a force = force x perpendicular distance of the force to the point.
The principle of moments states that for an object in equilibrium, the sum of the clockwise moments taken about the pivot must be equal to the sum of the anti-clockwise moments taken about the same pivot.
The centre of mass of the body is the point about which mass is equally distributed in all directions.
The centre of gravity is a single point where the whole weight of an object appears to act.
Stability of an object refers to its ability to return to its original position when the force that changed its orientation is removed.
Frictional force is the force that resists the motion of objects on a surface.
Terminal velocity is the maximum constant velocity that a body can achieve while passing through a resistive (viscous) medium.
Centripetal force is the force that compels a body to travel in a circular path. It may be electric, gravitational, or any other force.
Orbital velocity is the speed of an object revolving around another heavy object in an orbit.