Friday, 22 May 2015

How do the measurements of a standardised rugby league ball affect the place kick?

The specific measurement and shape of the rugby league ball (determined by the International Rugby Board) give it certain biomechanical characteristics to be exploited by the players.

As seen in the figure on the right, the measurements of a
standard rugby league ball are as follows:
Shape: Prolate spheroid
Length: 28-30 centimetres
 Width: 18.5-19.7 centimetres
End to end circumference: 74-77 centimetres
Width circumference: 58-62 centimetres
Weight: 410-460 grams




The Answer: The shape of a rugby league ball is described as a rounder, egg like shape which can be referred to as the prolate spheroid (Lemoine & Naami 2013). A prolate spheroid is spheroid that allows a rotation around the major axis, which enforces a backward motion after the ball has been kicked allowing for greater distance to be traveled and a predictable flight path. The length, width and circumference of the ball make it less aerodynamic than an Australian Rules football; however, its wide berth allows it to be more stable so that it can be kicked a greater distance with more accuracy, which is important for the place kick. The weight of the rugby ball is typically heavier than Australian Rules footballs to reduce the effect of air resistance and high winds but, is still light enough to be easily carried during play. 

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