Question

Let us assume that the net torque on a body is given as
(a) Zero (b) not zero. What will be the effect of this experiencing torques on the body in both the cases?

Answer 1

Hint: The torque of a body can be found by taking the derivative of the angular momentum of the body with respect to the time change. If the angular momentum is constant for a body, then the body will be in stable equilibrium. This all will help you in solving this question.

Complete step by step answer:
Torque is defined as the amount of the force that will be the reason for the rotation of an object about an axis. Torque can be taken as the rotational equivalent of the force in classical mechanics. Similar to the force causing acceleration, torque is the quantity which will cause an angular acceleration.
As we all know, torque is defined as the rate of variation of the angular momentum. That is we can write that,
$\vec{N}=\dfrac{d\vec{L}}{dt}$
Now let us consider that the torque is zero. Therefore the angular momentum is a constant and the object will be in stable equilibrium. Let us assume that the resultant torque is not being zero, then the angular momentum will be changing with respect to the time. Because of this angular acceleration will be there. The body will be thus in unstable equilibrium. Therefore the body will start to rotate.

Note: Angular momentum is otherwise known as the moment of momentum and also as the rotational momentum. It is taken as the rotational equivalent of linear momentum in classical mechanics. It is an important quantity as it is a conserved one. That is the resultant angular momentum of a closed system is found to be constant.