The first law of motion, also known as Newton's First Law of Motion or the law of inertia, actually doesn't explain why objects slow down and stop. It explains why objects tend to stay in motion at a constant velocity.

Here's why:

* Newton's First Law: An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

The reason objects slow down and stop is due to friction and other forces:

* Friction: This is a force that opposes motion between two surfaces in contact. When you push a box across the floor, friction between the box and the floor slows it down until it eventually stops.

* Air Resistance: This is a type of friction caused by the air pushing against a moving object. The faster the object moves, the greater the air resistance.

* Gravity: Gravity pulls objects towards the Earth's center. If an object is thrown upwards, gravity will slow it down and eventually bring it back to the ground.

In summary, Newton's First Law tells us that objects won't change their motion unless acted upon by a force. It's the forces like friction, air resistance, and gravity that actually cause objects to slow down and stop.