Wednesday, November 23, 2011

The Physics of a Water Polo Shot

In water polo a player can shoot the ball as fast as 50 miles per hour without contact with a surface to provide force and stabilization.  I want to explain how a water polo shot works and consider a few physics concepts that are at work in scoring a goal.
Procedure:
1)    Player lifts the  ball out of water with his/her shooting arm raised above the shoulder and trunk rotated away from the goal
a.     Non-throwing arm is outstretched in the direction of the goal for aim
2)    The player raises their body as high out of the water as possible to minimize FD
3)    Shot is initiated by rotation of front arm away from goal and trunk rotation toward goal
a.     As the trunk is rotated forward, the throwing arm is left behind for greater potential energy due to FT in triceps and shoulder muscles
4)    The shoulder is rotated and elbow extended to release the ball
a.     Trunk lean is away from shooting arm to improve position relative to the axis of rotation (spine) and maximize velocity
5)    The wrist snaps for follow-through and fingers can be used to provide spin on the ball

Many of these procedures are similar to throwing a baseball with a few special considerations due to  the fact that the player is never in contact with the ground and does not have a stabilizing force. In water polo, the action of the legs is key for support, balance, and production of force behind the shot.  During the shot there are several key actions of the legs to aid in balance and force production.  The player starts with their non-shooting-side foot pointed to ward to goal for aim.  Force is produced during the shot by “snapping” in the shooting-side foot to initiate trunk rotation.  During the forward swing, the non-shooting-side leg is forcefully extended to achieve force balance from the upper body rotation.
The key physics concepts used in scoring a goal in water polo are buoyancy and drag force, tension of muscles, angular momentum, and distribution of forces.
Videos:
Some great water polo shots: (showed shot at 4:39 in class)

A clip from the movie “Children of Glory” about the "Blood in the Water" match between Hungary and the USSR at the 1956 Melbourne Olympics during the Hungarian Revolution. It is a fun video to watch, but we only saw a clip of the penalty shot at 3:34.
Post written by Kelsie Anson


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