Suppose you are playing baseball and hit a home run. what forces slow down the ba while it is in motion? if you hit a home run in space, what would happen

Air resistance slows down the ball

In space, there would be no air resistance

Explanation:

When an object moves through the air, there is a force acting in the opposite direction to the motion of the ball: this force is called air resistance.

Air resistance is due to the friction between the molecules of air and the molecules at the surface of the object - because of this frictional force, the object is slows down in its motion and loses some energy (which is converted into thermal energy of the surrounding air).

There is also the force of gravity (downward) that acts on the ball: however, this force does not slows down the ball in its motion, instead it accelerates it towards the ground.

In space, however, there is no air and no gravity. This means that there are no forces acting on the ball: therefore, the ball will not be slowed down, and therefore will continue its motion forever, at constant velocity, according to Newton's first law:

An object at rest (or in motion) will stay at rest (or in motion at constant velocity) when the net external force acting on it is zero