I think this would be the definition from most positions. An object is in motion when its distance from another object is changing.Whether the object is moving or not depends on your point of view. For example, a woman riding in a bus is not moving in relation to the seat she is sitting on, but she is moving in relation to the buildings the bus passes. A reference point is a place or object used for comparison to determine if something is in motion. An object is in motion if it changes position relative to a reference point. You assume that the reference point is stationary, or not moving.