An object sliding across a rough table slows down and stops. What causes the slowing?

1. Making a surface smoother lets an object slide farther before stopping. 2. Extrapolating to a frictionless surface, the object would slide in a straight line indefinitely. 3. Friction is therefore the cause of the slowing, and it is an external force. 4. Inertia is a property rather than a force, so it cannot slow anything down. 5. Weight and the normal force act vertically here and cancel, so neither opposes the sliding. _Source: OpenStax College Physics (CC BY 4.0), Ch 4 "Dynamics: Force and Newton's Laws of Motion", section 4.2 Newton's First Law of Motion: Inertia_