Question

While specifying whether the body is at rest or in motion, why do we need an observer

Answer 1

According to Einstene every motion is relative that is we can say a body is in motion onlywith respect to another body Suppose if we are in a mus carrying an apple,withrespect to us,the apple is not in motion but to a man standing outside,both we and the apple in our hand is in motion So it depends to an observer thats why While specifying whether the body is at rest or in motion we need an observer