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The only force acting on the body when there is no air resistance is gravity, hence any other external force has no effect on the body's horizontal velocity. The horizontal velocity is perpendicular to the gravitational force and, as a result, tends to be unaffected by it. Gravity, as we all know, works downwardly or in the direction of the earth.

The situation alters, though, when air resistance is present. Similar to the viscosity that a moving body encounters in a fluid, air resistance is the force that opposes the motion of a body in the atmosphere. The opposing force is not by nature conservative.

In the absence of air resistance, there will be no drag for baseball. The baseball started falling downward after reaching the highest point. The speed of baseball becomes zero at the highest point due to gravity.

As the baseball started falling down the speed of baseball increased with fall. There is no air resistance so the speed of the baseball increases to ${\mathrm{v}}_0$until it reaches its initial position. The speed of baseball remains the same in the absence of air resistance.

The speed of baseball also increases in the presence of air resistance during downward motion but up to a certain speed after that ball achieves a speed called terminal speed. The speed of baseball becomes less when it reaches its initial position due to the drag force on the baseball.