Newton's first law says a body at rest stays at rest unless acted on by:

1. Everyday experience suggests moving things naturally slow down and stop. 2. Newton's first law states that a body at rest remains at rest, or, if in motion, remains in motion at a constant velocity unless acted on by a net external force. 3. So a change in velocity always needs a cause. 4. Internal forces cancel within a system and cannot change its motion. _Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 4 'Dynamics: Force and Newton's Laws of Motion', sections 4.1-4.8_