1. The roughness of the ball.
The amount of roughness will determine at what critical speed is needed to create the 'knuckling' effect on the ball.
Knuckling effect: when the ball does not spin or spins very little.
Magunus effect: when the ball spins like a 'banana kick'.
For the Jabulani which is a more smoother ball with more seams compared to the Brazuca, experts have stated that the seams affects the accuracy of the ball path. The smoother the ball the higher speed at which the ball knuckles.
Just to compare some figures, the older more traditional balls stitched internally had 32 panels where the knuckling effect occurred around 48km/h.
With the smoother Jabulani ball the numbers were more like 50km/h. (during a free kick.)
This year the Brazuca ball is more rough textured and has dimples on the outside which will help stabilised the ball better.
2. The Geometry of the ball
- The number of seams on the ball plays a big role on determining roughness.
- Also the depth of the seams also influence the aerodynamics.
- Length of the seams
Brazuca: RIGHT and Jabulani LEFT
I am not a physicist and when talking about low pressure and wake I became a bit lost, but basically a rougher balls travel further through the air more efficiently for example, how the football seams agitates the air, the dimples on a golf ball, or the fluff on a tennis ball. The agitation is necessary for fast and reliable flight path. A perfectly smooth ball experiences large amounts of drag force.
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