An object sliding across a table slows down because of the net force of:

1. Newton's first law says the object would keep moving if nothing acted on it. 2. Something must therefore be acting. 3. An object sliding across a table or floor slows down due to the net force of friction acting on it. 4. Friction is thus the cause of the slowing, consistent with Newton's first law. _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_