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Moment of Force Concept of Torque: In Newton s Laws of Motion we have studied that that if a body is at rest and has to be brought in motion , we must apply a force. Similarly, in order to Stop a moving body we must apply a Force. Thus Force is actually the cause of Translational Motion. On Application of force , the body attains a Linear acceleration(a). However, in order to produce Rotational Motion in the body force must be applied in a different way because not all forces have the ability to rotate the body. Rotation is always caused by a pair of forces (called couple). These pair of forces must be equal in magnitude , opposite in direction and must act on different points in the body. Together , they cause the body to rotate and this turning effect of the couple forces is termed as torque. Thus we can conclude that whatever role Force plays in Translational Motion, Torque plays the same role in Rotational Motion. For this reason , Torque is also known as the Rotational Analogue of Force. Whenever , Torque acts on a body , attains an angular acceleration. If I ask you , Does a body require force to stay in motion? . Well , of course not because the body which was already moving with uniform velocity will continue to do so even if no force acts on it due to inertia of motion. However , you will agree that if the body was initially at rest , it does require force to come into Translational Motion. Similarly,
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