5 ms·

The physics of that ‘kickalicious’ kick

247 points by llambda 14y ago

aatish 14y ago
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.
- deleted 14y ago
  [deleted]
- TheAmazingIdiot 14y ago
  That is an awesome analysis of video and working through the physics. Complete aside: Mind exploded from unit mismatch. Miles per hour then meters? Gah.... Just please dont use gradians for angle measurement :)
  - aatish 14y ago
    haha - the 32mph was originally 14.4 m/s. Given that the top story here today is a white house petition to adopt the metric system in the US, I should know my audience better :)
- abcd_f 14y ago
  Analyze this - https://www.youtube.com/watch?v=ZQX8FakToj0 https://www.youtube.com/watch?v=ZQX8FakToj0 :)
- T-hawk 14y ago
  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 14y ago
    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.
- rm445 14y ago
  I think your assumption that good physics == not fake does not hold for certain classes of faking, i.e. simulating the collision first and modifying the ball positions (or creating one or both balls wholesale) to match. I mention this not to cast any doubt on the kicking video, but because there are a lot of good simulation tools nowadays and faking something up by working out the physics first is only going to get easier.
  - aatish 14y ago
    Well, if fakers make the effort to do the math (and physics), more power to them. It just makes this kind of video forensics a more interesting challenge. :) Here's another example of a physics based take-down (by Rhett Allain) of that eagle lifting a baby video that was doing the rounds. http://www.wired.com/wiredscience/2012/12/eagle-picks-up-a-kid-real-or-fake/ http://www.wired.com/wiredscience/2012/12/eagle-picks-up-a-k...
- borlak 14y ago
  Nice work, but these types of videos always annoy me. Anyone with the basics of athletic skill can perform these stunts with enough tries -- which the guy admitted to taking several tries. Some of the pure-power moves are out of the question for a lot of people, and those are definitely cool, but kicking balls into trashcans and basketball hoops is not. The exception would be doing several difficult moves in a row without fail.
  - sophacles 14y ago
    Yes, I could get a video of me doing a lot of these stunts. Great. Could I get all of them to happen in an afternoon of trying? Probably not. It would take a long time and a lot of luck to get any one of them. An interesting, and far more skill showing (imo) version of this video would be to show how close they were on each of the tries - If for example he was within a couple of meters of collision each attempt, I would call that very high skill. But if the other attempts were dozens of meters apart, the skill would be much lower.
    - ricardobeat 14y ago
      There are a handful of uncut scenes in the video where he repeatedly hits his target.
fla 14y ago
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=BURnfFozfO4#t=140s http://www.youtube.com/watch?feature=player_detailpage&v...
- jschulenklopper 14y ago
  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 http://www.youtube.com/watch?v=QfKFIzX7jSY
  - ChuckMcM 14y ago
    I think soccer bowling has a real shot at becoming an Olympic sport! :-)
evan_ 14y ago
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.
nhebb 14y ago
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 14y ago
  > 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 14y ago
    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.
- oh_sigh 14y ago
  Perhaps you should contemplate the phrase and its usage. The term "dumb jock" is always referring to dumbness, or a lack of care for, academic and intellectual pursuits. That's it. Your pedantism is confounding.
sixothree 14y ago
It seems to me that most of these kicks are better suited for a different sport.
- mahmud 14y ago
  Soccer. In fact, the acrobatic "freestyle soccer" sub-category.
chmod775 14y ago
Reminds me of Rémi Gaillard http://www.youtube.com/watch?v=Ps6s45Pg0To http://www.youtube.com/watch?v=Ps6s45Pg0To
yk 14y ago
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 http://sports.yahoo.com/nfl/players/4587/career
- jstclair 14y ago
  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 http://sports.yahoo.com/nfl/stats/byposition?pos=K
  - aptwebapps 14y ago
    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.
    - smackfu 14y ago
      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.
hardik988 14y ago
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 http://youtu.be/KNwLn85I75Y?t=1m25s
- kayoone 14y ago
  Sorry but that Ronaldinho video is a Nike ad and is obviously fake!
  - hardik988 14y ago
    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"?
    - alexkus 14y ago
      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.
kghose 14y ago
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.

247 points by llambda 14y ago

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.

deleted 14y ago
[deleted]
TheAmazingIdiot 14y ago
That is an awesome analysis of video and working through the physics. Complete aside: Mind exploded from unit mismatch. Miles per hour then meters? Gah.... Just please dont use gradians for angle measurement :)
- aatish 14y ago
  haha - the 32mph was originally 14.4 m/s. Given that the top story here today is a white house petition to adopt the metric system in the US, I should know my audience better :)
abcd_f 14y ago
Analyze this - https://www.youtube.com/watch?v=ZQX8FakToj0 https://www.youtube.com/watch?v=ZQX8FakToj0 :)
T-hawk 14y ago
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 14y ago
  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.
rm445 14y ago
I think your assumption that good physics == not fake does not hold for certain classes of faking, i.e. simulating the collision first and modifying the ball positions (or creating one or both balls wholesale) to match. I mention this not to cast any doubt on the kicking video, but because there are a lot of good simulation tools nowadays and faking something up by working out the physics first is only going to get easier.
- aatish 14y ago
  Well, if fakers make the effort to do the math (and physics), more power to them. It just makes this kind of video forensics a more interesting challenge. :) Here's another example of a physics based take-down (by Rhett Allain) of that eagle lifting a baby video that was doing the rounds. http://www.wired.com/wiredscience/2012/12/eagle-picks-up-a-kid-real-or-fake/ http://www.wired.com/wiredscience/2012/12/eagle-picks-up-a-k...
borlak 14y ago
Nice work, but these types of videos always annoy me. Anyone with the basics of athletic skill can perform these stunts with enough tries -- which the guy admitted to taking several tries. Some of the pure-power moves are out of the question for a lot of people, and those are definitely cool, but kicking balls into trashcans and basketball hoops is not. The exception would be doing several difficult moves in a row without fail.
- sophacles 14y ago
  Yes, I could get a video of me doing a lot of these stunts. Great. Could I get all of them to happen in an afternoon of trying? Probably not. It would take a long time and a lot of luck to get any one of them. An interesting, and far more skill showing (imo) version of this video would be to show how close they were on each of the tries - If for example he was within a couple of meters of collision each attempt, I would call that very high skill. But if the other attempts were dozens of meters apart, the skill would be much lower.
  - ricardobeat 14y ago
    There are a handful of uncut scenes in the video where he repeatedly hits his target.

fla 14y ago

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=BURnfFozfO4#t=140s http://www.youtube.com/watch?feature=player_detailpage&v...

jschulenklopper 14y ago
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 http://www.youtube.com/watch?v=QfKFIzX7jSY
- ChuckMcM 14y ago
  I think soccer bowling has a real shot at becoming an Olympic sport! :-)

evan_ 14y ago

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.

nhebb 14y ago

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 14y ago
> 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 14y ago
  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.
oh_sigh 14y ago
Perhaps you should contemplate the phrase and its usage. The term "dumb jock" is always referring to dumbness, or a lack of care for, academic and intellectual pursuits. That's it. Your pedantism is confounding.

sixothree 14y ago

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

mahmud 14y ago
Soccer. In fact, the acrobatic "freestyle soccer" sub-category.

chmod775 14y ago

Reminds me of Rémi Gaillard http://www.youtube.com/watch?v=Ps6s45Pg0To http://www.youtube.com/watch?v=Ps6s45Pg0To

yk 14y ago

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 http://sports.yahoo.com/nfl/players/4587/career

jstclair 14y ago
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 http://sports.yahoo.com/nfl/stats/byposition?pos=K
- aptwebapps 14y ago
  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.
  - smackfu 14y ago
    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.

hardik988 14y ago

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 http://youtu.be/KNwLn85I75Y?t=1m25s

kayoone 14y ago
Sorry but that Ronaldinho video is a Nike ad and is obviously fake!
- hardik988 14y ago
  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"?
  - alexkus 14y ago
    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.

kghose 14y ago

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.