Define the state of rest and the state of motion of an object.

Consider a person sitting inside the bus and the bus is moving. For the observer, sitting next to this person, will conclude that the person is in the state of rest because its position is not changing with time but this person is in the state of motion for the observer, observing him from the road.

Final Answer: Hence, when the position of the object is not changing with respect to the observer it is said to be at rest and if it is changing it is said to be in the state of motion.