
The physics of that ‘kickalicious’ kick - llambda
http://www.empiricalzeal.com/2012/12/31/the-physics-of-that-kickalicious-kick/?src=search
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aatish
Hi- I'm the author of the piece (on twitter at @aatishb) and am happy to field
questions on the post. Do people accept that the video isn't faked? The data
isn't perfect, but it was good enough to convince me that the video is real.

Here's a follow up question, that I haven't thought much about. Assume that
Rugland launches the first ball at 64 degrees and at 14.4 m/s (about 32 mph).
1.5 seconds later, and 1.5 meters ahead, he kicks the second ball. (So far
these are the numbers I get from the data). My question is, given the size of
a football, how accurate does he need to be in the launch speed and angle of
the second ball, in order to be able to strike the first ball?

You might need to assume a reasonable range for the launch speed to work this
out.

~~~
T-hawk
Here's a first-order approximation. I'll assume the angle is perfect and work
out the speed range. The first ball decelerated to maybe 8 m/s given its
altitude at collision and some loss to air friction. If the ball is 25 cm
wide, it crosses its own diameter in 1/32 second.

Assume the distance of the collision is 10m from launch and occurs 1.7 seconds
after the second kick. The margin of error on the arrival time is 1/32 / 1.7 =
1.84%. Using your launch speed centered around your value of 38 mph = 16.9875
m/s, that means the possible range was 16.675 to 17.300 m/s. Interestingly,
that's a difference of 1.4 miles per hour, which is also roughly the precision
of velocity that baseball pitchers can produce on demand.

By the way, there's more variables on the inputs to the second ball. The
timing of the kick is important and controllable too, creating a three-
dimensional map of inputs. This could be transformed into and visualized as a
3D graph, showing all the combinations of speed/angle/timing that will result
in a collision.

Also, the left-to-right angle must be on target too or the balls won't be in
the same vertical plane for any collision at all.

~~~
Someone
About the vertical angle that you assumed to be perfect: I don't think that is
critical. If you hit the second ball a bit higher/lower than intended, it
crosses the trajectory of the first ball higher/lower than intended, so it
must be at the intersection point earlier/later. Luckily, you get some of that
for free, as the intersection point will be closer by/farther away.

All else being equal, the harder you can kick, the easier this gets. The lower
the arc of the first ball, the smaller the angle of intersection between the
two trajectories, and the easier the hit. You can get a lower arc by giving
the ball more horizontal speed, keeping vertical speed the same (just
decreasing vertical speed won't help; the first ball would hit the floor
before you can hit it with the second ball)

Of course, all else isnt equal; directional errors likely are some function
increasing with both distance and ball speed.

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fla
Human are capable of amazing things. Rémi Gaillard has for example been known
for this very specific skill for years.

One example can be viewed at
[http://www.youtube.com/watch?feature=player_detailpage&v...](http://www.youtube.com/watch?feature=player_detailpage&v=BURnfFozfO4#t=140s)

~~~
jschulenklopper
And capable of funny things as well. This is a 2009 video of that same guy who
roams the streets of Montpellier with apparently some soccer balls to spare:
<http://www.youtube.com/watch?v=QfKFIzX7jSY>

~~~
ChuckMcM
I think soccer bowling has a real shot at becoming an Olympic sport! :-)

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evan_
First of all- I totally buy that this video is legit, it would probably simply
be easier to actually make all of these kicks than it would be to fake the
videos. Plus, he's not saying he can make that kick every time, he freely
admits that it took him many tries, so while it's impressive it's not so
superhumanly accurate that it's impossible to imagine.

But, if I were going to fake the video, I'd have my kicker kick the first ball
for real and mime kicking the second (or if that looks fake, really kick a
second ball but paint it out)- and then use the same video physics package
this guy used to predict where the balls should be at time t, painting the
second ball (and both balls, after they "collide") in, frame-by-frame, on the
path it charts out.

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nhebb
And here we have empirical (zeal) evidence that should make you reconsider
calling someone a "dumb jock". Rugland calculated in his head what a PhD in
Physics worked out on paper. We call it coordination. I look at it as another
facet of intelligence.

~~~
philh
> Rugland calculated in his head what a PhD in Physics worked out on paper.

Besides that the problem doesn't begin to approach PhD-level...

You could probably say the same thing of me when I'm running or cycling. But
whatever calculations my brain performs, the results are not accessible to
myself or to anyone else; and I can't tell my brain what calculations to
perform, so I can't tell anyone else what angle to lean at, and if I go to the
moon I will have to let it work out for itself that gravity is not a universal
constant.

You could also say the same thing when a cat twists in midair to land on its
feet, "using" the principles of angular momentum. (Scare quotes because the
cat has no idea what angular momentum is.)

Rugland's feat is certainly impressive. (And in a different class to my
examples, in that he doesn't get constant feedback; if my balance is wrong I
can adjust, if he kicks wrong the ball misses. But you could describe my
feedback-integration using complicated physics as well, so I don't think that
invalidates my point. I'm pretty sure "knife throwing" and "blindfold
juggling" would have been suitable examples, but I don't personally possess
those skills.) And I'm certainly not saying he's stupid.

But to call this intelligence, seems to be extending the word far beyond its
usual boundaries.

~~~
gadders
I wonder if there is a way to make the results of those calculations visible?
i.e. you can't calculate an intersection of two arcs, but if a VR environment
showed you a ball and said "Throw another ball to hit it", could you then get
a good approximation? Just thinking out loud.

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yk
Nice video and analysis, but the big animation programs all contain simulation
packages, which will calculate precisely this, it may even be easier to
simulate the collision than to animate by hand. ( And what really put me off
in the video is the use of time lapse in the repeated kicks, precisely at the
moment where one could hide a cut.)

On the other hand a NFL level kicker is roughly 50% for 50+ yard field goals.
[1] Therefore the 5 50 yard field goals should be possible for an NFL kicker
in something like 2^5/2=16 tries. ( Similar for the 60, 50 etc sequence, using
again the stats,

1/3.* (24./47)* (96./141.)* (120./136)* (119/121.) = .1

it should require something like 10 tries. ( Assuming a probability of 1/3.
for the 60 yrd.) So I think the video is genuine, but only because I wonder
why anyone would spoil an impressive video by just one special effects shot.)
To really convince me, one would need to calculate the kick of the second
ball, since this is the moment where animation and reality have to match.

[1] e.g. David Ackers 24 - 47 for 50+
<http://sports.yahoo.com/nfl/players/4587/career>

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jstclair
Actually, for 2012, kickers are 61% for 50+ yard field goals [1], including an
incredible 10/10 performance.

[1] <http://sports.yahoo.com/nfl/stats/byposition?pos=K>

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aptwebapps
I bet they do better in practice on an empty field than in a game where they
have a limited amount of time and a bunch of big guys headed their way quick.

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smackfu
This has always amazed me when basketball players are practicing. For the
shots they specialize in, their miss rate is 0% with no guarding or pressure.

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kghose
I remember a section from Feynman's "Surely you are joking..." where he says
he went over a textbook chapter for Newton's laws and found a graph,
purportedly from an experiment where they rolled a ball down an inclined
plane. He says the graph followed the equations perfectly, with a little
Gaussian noise sprinkled in, but they had neglected to account for the
rotational inertia of the ball, and so he concluded that the 'experiment' was
faked.

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sixothree
It seems to me that most of these kicks are better suited for a different
sport.

~~~
mahmud
Soccer. In fact, the acrobatic "freestyle soccer" sub-category.

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hardik988
I'm more of a soccer fan, and there's this video of a famous soccer player
Ronaldinho doing the "crossbar challenge" - from about 30-40 yards out, he
repeatedly hits the crossbar with a soccer ball, only to have it come back to
him. The precision required to pull of such a feat is just mind boggling.
<http://youtu.be/KNwLn85I75Y?t=1m25s>

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kayoone
Sorry but that Ronaldinho video is a Nike ad and is obviously fake!

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hardik988
I knew it was an ad. But, I wouldn't be surprised if a professional soccer
player could pull that off. Also, could you tell me why you think it is
"obviously fake"?

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alexkus
I've played soccer for years, including with some ex-professionals and I'd be
very surprised if any player could hit the crossbar that many times in a row
from that distance with that precision. The bit that screams "obviously fake",
for me at least, is the near perfect return trajectory each time.

Hitting the crossbar requires kicking something ~8.5" in diameter at something
5" wide so you've got a 'window' of 22" to aim at. With practice you might be
able to do it 3/5 times from 20 yards.

(3/5)^4 =~ 1/8

So 8 tries to do it 4 times in a row.

To get the ball to come back like that each time the 'window' is now about 1"
(if that). Outside that window and it bounces down to the ground, or glances
the bar and goes behind the goal, or bounces way up in the air and never
returns to you. So each kick is now 3/(5x22) and (3/(5x22))^4 = 1 in 1.8
million. Good luck.

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chmod775
Reminds me of Rémi Gaillard

<http://www.youtube.com/watch?v=Ps6s45Pg0To>

