Calculating the possible trajectory of a soccer ball

July 13, 2004 8:00 AM

Soccerfilter: We've seen Beckham bend it. But what's really the most acute angle you can curve a football? Can it like 'boomerang'? I ask this to settle a very very very serious argument.
posted by timyang to science & nature (6 comments total)

You pretty much don't bend it more than this. (3,4 MB mpg)
posted by mr.marx at 8:22 AM on July 13, 2004

Wow...that clip is amazing, mr. marx.

tim, I'm not sure about the answer to your question, but one key issue is whether you're talking about the absolute aerodynamic properties of a soccer ball--how much you could curve the trajectory if you potentially used a machine to strike it, under idealized conditions--or whether you're asking how much a human being could practically be expected to bend a kick.

If you presume an invincible soccer ball that wouldn't explode under impact, and a machine that could put the ball under any amount of force and spin, then you could probably do some pretty impressive things.

In practice, though, it's hard to imagine doing much better than the guy does in mr. marx's clip (although I'm happy to be proven wrong).
posted by LairBob at 8:34 AM on July 13, 2004

That clip has to rate as one of the finest free kicks ever. I'm not sure even Roberto Carlos could do that again. It's a truely freakish ammount of movement and power in a shot and he has tried many times to do it again without such dramatic effects.

Recent shots with exagerated curve that I've seen include Zidane's free kick against England and Marek Heinz's free kick against Germany in the recent European Cup finals. Neither of them moved the ball quite so much as Carlos though.

I'd venture that a boomerang shot would not happen unless the balls get lighter and a match is played in a wind tunnel.
posted by davehat at 8:41 AM on July 13, 2004

From"The Physics of Football":

"Carlos kicked the ball with the outside of his left foot to make it spin anticlockwise as he looked down onto it. Conditions were dry, so the amount of spin he gave the ball was high, perhaps over 10 revolutions per second. Kicking it with the outside of his foot allowed him to hit the ball hard, at probably over 30 ms-1 (70 mph). The flow of air over the surface of the ball was turbulent, which gave the ball a relatively low amount of drag. Some way into its path - perhaps around the 10 m mark (or at about the position of the wall of defenders) - the ball's velocity dropped such that it entered the laminar flow regime. This substantially increased the drag on the ball, which made it slow down even more. This enabled the sideways Magnus force, which was bending the ball towards the goal, to come even more into effect. Assuming that the amount of spin had not decayed too much, then the drag coefficient increased. This introduced an even larger sideways force and caused the ball to bend further. Finally, as the ball slowed, the bend became more exaggerated still (possibly due to the increase in the lift coefficient) until it hit the back of the net - much to the delight of the physicists in the crowd."
posted by Otis at 8:53 AM on July 13, 2004

Holy fuck.
posted by signal at 9:11 AM on July 13, 2004

Thanks Mr Marx and Otis! That's was a truly perfect shot!
posted by timyang at 8:23 PM on July 13, 2004