1. Newton's first law tells us Consider a body on which no net force acts 1)If the body is at rest, it will remain at rest; 2)If the body is moving with constant velocity, it will continue to do so, no force is needed to keep it moving1. Newton’s first law tells us: Consider a body on which no net force acts. 1) If the body is at rest, it will remain at rest； 2) If the body is moving with constant velocity, it will continue to do so, no force is needed to keep it moving