Important Forces |
These forces influence the ball at particular stages of the serve. The are presented in the order in which they influence the ball when it is being served. |
Force Due to Gravity
Gravity is a crucial force in many aspects but especially in a volleyball serve. Any time a server makes an effective serve to score a point, they have gravity in part to thank. Regardless of which serving technique is utilized, the ball is thrown into the air before contact is made. Have you ever stopped to think about the physics behind this? The server first exerts an upward, and then forward, force on the ball. While this is happening, gravity is simultaneously exerting a downward force on the volleyball. Without this downward force, the ball would never land on the opponents side. Gravity's presence is so great and so constant that many people forget of its existence. Most take gravity into account by accident, because that is all they know. It takes a real physics lover to appreciate the manifestation of gravity in even the simplest of actions, like serving a volleyball.
Air RESISTANCE
Air resistance, or drag, is a force that opposes the motion of the ball. The force always acts in a direction that is opposite to that of velocity, and its magnitude is proportional to the square of speed- mathematically represented as ||Fdrag|| = Kd||v||2.
Force from spin
This is easily the coolest and most complex force that acts on the volleyball during a serve. Volleyball players and observers alike will tell you that when a player puts topspin on the ball, the airborne time of the ball is reduced. Clearly the force of Earth is not changing, so what is to blame? The answer lies in an aerodynamic force known as the magnus effect. When a ball spins, friction between the ball and the air causes the ball to react in the direction of the spin of the ball. When a ball experiences top spin, the velocity of the air around the ball's top half becomes less than the air velocity around the bottom half of the ball. As the resultant air speed around the top half is less than the air speed around the ball's bottom half, the pressure is greater on top of the ball (due to Bernoulli's principle). The result is a net downward force, making the ball drop to the ground faster than if it had no spin. This is the exact reason many volleyball players elect to utilize a jump serve, because while it is harder to execute, it is difficult to return if done correctly. The magnitude of the force due to spin is proportional to the angular velocity and to the velocity of the volleyball. That is, ||Fs|| = Ksω||v||. Still confused? Learn more here.