Forces on a Tennis Ball

Thrust - momentum of the racquet pushing the ball forward.
Gravity - the weight of the ball acts downward from the ball’s center of gravity.
Drag - refers to the force, in this case - air resistance, acting in the opposite direction (flight direction) of the movement of an object.

Lift - is the force opposite to gravity that acts against the weight of an object to move it upward.
Topspin - spin put on the ball by striking it a certain way with the racquet that disrupts the aerodynamics and forces the ball to pushed down.
Backspin - spin put on the ball by striking it a certain way with the racquet that disrupts the aerodynamics and forces the ball to pushed up.