Question

Can an object be in equilibrium if it is in motion?

Answer 1

Hint: Equilibrium is defined as the condition in which the net force acting on a body is zero. For a single particle, equilibrium arises if the vector sum of all forces acting upon the particle is zero. There are two types of equilibrium- static equilibrium and dynamic equilibrium.

Complete answer:
It is true that an object can be in equilibrium even if it is in motion. This type of equilibrium is defined as dynamic equilibrium. Dynamic equilibrium is a state of equilibrium where bodies are moving at a constant velocity.

As we know, an object is said to be in equilibrium, if the net force acting on it is zero. So, according to the second law of motion, the acceleration will also be zero and thus, the velocity of the particle will be uniform. Zero acceleration means that either the object is at rest or moving with a constant velocity.

Thus, an object in equilibrium can be in motion.

Additional information: Static equilibrium is the state of equilibrium in which the object is at rest and is not moving. The most common example of static equilibrium is a book kept on the table. In this case, there are two forces acting on the book- gravitational force and the normal force but the net force due to them is zero as both the forces are equal and opposite. Also, since the book is at rest, this is a condition of static equilibrium.

Note: When we define equilibrium then the most simple definition is that equilibrium is a point where the net external force and the torque acting on the body about the centre of mass results in zero. But in order to be more specific about rigid body equilibrium, it is a combination of both translational equilibrium and rotational equilibrium.