Question

how do we usually judge the state of rest or of motion of a body

Answer 1

by its inertia is rest and motion

Answer 2

QUESTION --- how do we usually judge the state of rest or of motion of a body ?

Motion is a relative term.
We judge the state of rest or motion of a body with respect to the surroundings of the body or either with Time.

Example ---- A man travelling in Train is in state of rest with respect to the seat, fan or other passengers in the train. But he is is state of motion with respect to objects out of the train i.e. Tree or a farmer in the field.

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