When Do You Say A Body is Moving?Suppose you were born inside an artificially illuminated, completely closed house and continue to live there, would you ever know that the earth under you is moving? When you hold your bag and travel in a bus from home to school you do not feel your bag is moving. But it has moved with you from one place to another!
All along the journey, the bag did not change its position with respect to you. Hence, it was at rest with respect to you. But it has changed its position from home to school. Hence, if the fixed point of reference is your home, the bag is said to have moved! Thus, the fixed point of reference, called the origin, is very important to say whether a body is moving or is at rest. Hence, we say, motion and rest are relative.
We say that a body is moving if it changes its position with respect to its surroundings (or a fixed point).