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VOLLEYBALL

A Top-Spin vs. a Floating Serve

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Extension Exercises:
Movement patterns during 
the volleyball serve


Analysis of the parameters 
of a serve


The flight path of a 
volleyball serve

 

Biomechanical Principles to be Investigated
Bernouilli’s Principle and the Magnus effect

Purpose
An individual or object that leaves the ground and moves freely through the air is termed a “projectile”.  The flight path of a projectile is affected by the downward pull of gravity, lift forces, drag forces, the magnitude of the initial velocity imparted to the projectile, the angle of attack and the location at which the initial velocity was imparted to the individual or object with respect to its center of mass (i.e., was a spin imparted to the projectile?).  The mass of the projectile dictates how much effort must be expended to launch it into the air.  Whereas, the size, shape and orientation of the projectile in flight will dictate the extent of the lift vs. the drag forces.  Why?  This lab will investigate the amount of drag and lift forces affecting the flight path of a volleyball during two different types of serves – a floating serve and a top spin serve.


Rationale
Bernouilli’s Principle expresses the inverse relationship between the flow velocity at any given location on a projectile and the amount of pressure exerted against that location.  It states that “Where the flow velocity is fast, the pressure is low.  Where the flow velocity is slow, the pressure is high.”  A lifting force is created by a difference in pressure applied to opposite sides of a projectile.  The direction of its application is perpendicular to the air flow moving past the projectile.

Unlike the uniform shape of most aircraft wings, which are designed to minimize drag forces and maximize lift forces at take-off; sports implements vary in shape, composition, texture and size.  Minimization of drag forces when launching sports projectiles is typically a desired outcome during most throwing, striking or kicking movement patterns.  However, this requires spinning the projectile to stabilize its flight path and an attack angle unique to each sport.

For example, a top spin volleyball serve enhances the lift force in the direction of the spin [i.e., ascent phase (forward and downward), mid-flight (downward) and descent phase (backward and downward)] while decreasing the drag forces encountered in flight.  Imparting spin to a projectile to cause a lift force in a desired direction is referred to as the Magnus effect.  The spin induced lift force is referred to as the Magnus force.

An exception to the often employed attempt to minimize drag forces at launch and during the flight of a projectile can be observed when a floating serve is used. Spin is not imparted to the volleyball and the drag forces exerted against it in flight create an erratic flight path.  The most effective volleyball servers are those who vary the use of floater and top spin serves to keep the opposition off-guard.

References
Kreighbaum, E. & Barthels, K.M. (1996).  Biomechanics (4th ed.).  Boston:  Allyn and Bacon

Widule, C.J. (1974).  An Analysis of Human Motion, 156-176.  Lafayette, IN: Balt.