
How does a soccer ball swerve? - srikar
https://newsoffice.mit.edu/2014/explained-how-does-soccer-ball-swerve-0617
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nkurz
The paper referred to is here: The aerodynamics of the beautiful game by
J.W.M. Bush

[http://math.mit.edu/~bush/wordpress/wp-
content/uploads/2013/...](http://math.mit.edu/~bush/wordpress/wp-
content/uploads/2013/11/Beautiful-Game-2013.pdf)

    
    
      one can only be puzzled to note that striking a smooth   
      beach ball or an old, worn volleyball with spin has just 
      the opposite effect
    

I'm having great difficulty believing this. I've spun many beach balls and
struck man old, worn volleyballs and have never seen a ball curve the wrong
way. I've also dealt with many smooth ping-pong balls, and have even sanded
off the dimples on golf balls to see the aerodynamic effect.

I'm not saying it's mathematically impossible, just that I didn't think it
would be possible to find this effect in the real world. Maybe I've just never
tried something smooth enough. Is there some reasonable home demonstration of
this that I can try to prove it to myself? They say they did it with a latex
band around a soccer ball?

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rcthompson
It sounds like the effect depends on whether the surrounding airflow is
turbulent or laminar. I believe that making an object smaller biases the
airflow more to turbulence, so ping pong balls and golf balls may be too small
to show the negative effect at their respective game-relevant velocities.

Also, just having a rough surface texture can be enough to cause turbulence,
since it causes the air to stick more to the surface. In my experience, ping
pong balls have a definite texture to them, and unless you polished that
sanded-down golf ball to a mirror finish, it probably has a non-smooth texture
too.

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rjtavares
Pirlo's free kick mentioned in the article:
[http://gfycat.com/CourteousHatefulBat](http://gfycat.com/CourteousHatefulBat)

Roberto Carlos' free kick:
[http://www.youtube.com/watch?v=Pl0LHM-33Io](http://www.youtube.com/watch?v=Pl0LHM-33Io)

~~~
kokoloko
Notice how the ball in Pirlo's free kick is barely spinning, goes very fast
and the path is very unpredictable. It's called a "Folha seca" and it exploits
the turbulences to make the ball drop at the last moment. Very spectacular,
but hard to score consistently.

~~~
eyko
It's spinning, and the amount of curve matches the amount of speed. The
unpredictability comes from the fact that the axis is also spinning, but very
slowly. It's hard to get the topspin and rotation on the ball, and still hit
the target. But these guys train shots for a living.

~~~
dmoo
If you have a few minutes have a look at Juninho, one of the best ever.
[https://www.youtube.com/watch?v=NesfdRNtwsE](https://www.youtube.com/watch?v=NesfdRNtwsE)

Also don't forget the boots are designed to work the ball, for example
[http://en.wikipedia.org/wiki/Adidas_Predator](http://en.wikipedia.org/wiki/Adidas_Predator)

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nrzuk
Football*

:)

~~~
thret
Friend of mine recently did a stand up about this, it's a little NSFW
(c-bomb):
[https://www.youtube.com/watch?v=82mMuSZPohM#t=00m38s](https://www.youtube.com/watch?v=82mMuSZPohM#t=00m38s)

~~~
Dewie
[https://www.youtube.com/watch?v=dF1NUposXVQ](https://www.youtube.com/watch?v=dF1NUposXVQ)

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neves
I thought Hacker News were the only place of the world where soccer weren't a
conversation theme.

~~~
JetSpiegel
Run to the hills!

