Question

What is the equilibrium rule?

Answer 1

The equilibrium rule states that if the net force or net torque acting on the system is zero then the body is said to be in equilibrium. This implies that neither the system will have an acceleration nor the system will have any angular acceleration if it is in equilibrium. If the system does not have an acceleration or an angular acceleration, then it could be at rest or could be moving with uniform speed or uniform angular speed.

Complete step-by-step solution:
The equilibrium rule says that if a system is in equilibrium then the sum of all the forces or the net force acting on the system is zero due to which the system does not experience any linear acceleration and remains at rest or moves with a constant velocity. We can write it down as:
$\sum{F}=0$
The equilibrium rule says that if a system is in equilibrium then the sum of all the torques or the net torque acting on the system is zero due to which the system does not experience any angular acceleration and remains at rest or moves with a constant angular velocity. We can write it down as:
$\sum{\tau }=0$

Note: The equilibrium rule is applicable to systems that are at rest as well as those systems that do not have any acceleration (linear or angular). For example: a stationary ball can be said to be in equilibrium if the sum of all the forces acting on it is zero, or a ball rotating with a constant angular velocity can also be said to be in equilibrium if the sum of all the torques acting on it is zero.