Dot Physics

Kobe Bryant Jumping Over a Car

We have all seen the Kobe Bryant video of him jumping over an Aston Martin – this keeps coming up on the Internet. There has been vast discussions of whether this is real or fake. I will do my best to examine the evidence. In short (in case you don’t want to read the whole thing) Kobe can most likely really jump that high, it is possible that there was some perspective trickery involved. Here is the video in case you are brand new to the WWW:

Oh – don’t forget I already analyzed Kobe Bryant jumping over a pool of snakes. I voted that was real.

First, let me give a personal note to Kobe and his friends:

  1. When making a video, please do not wear dark
    colors. Also, it would help if your outfit had
    distinguishing patterns on it. This video is very
    difficult to analyze because it is hard to see
    where you are (legs and arms and stuff). It would
    help if you wore a bright red cap or
    something.
  2. Your other video (of
    you jumping over a pool of snakes
    ) was much
    easier to analyze because you didn’t change your
    body position. Whenever possible, please do that
    again.
  3. I must give bonus points to your film crew.
    Thank you very much for not moving the camera while
    he is jumping and for having a nice perpendicular
    shot that does not need perspective correction (I
    still haven’t figure out how to do that).
  4. Finally, I know these jumps may be fun, but
    please be careful. Oh, the quality of videos on
    youtube pretty much sucks. I found one somewhere
    else that looked much better but it had repeating
    frames.
  5. Oh, one more. The next time you do a jump, send
    me a note and I will analyze it as soon as
    possible.

Ok, now on to the analysis. Question: was the jump
fake? Well, one way to answer this is to look at his
acceleration in the air. This is somewhat problematic
because he is not a rigid object while in the air. To
compensate for this, I will mark the location of his
important body parts and plot the motion of his
center of mass. Again, I use Tracker Video Analysis to get
x,y positions of each part in each frame. I
tracked the motion of his calf, thigh, trunk,
arms and head. To find the y-value of the center
of mass, I used:

i-0ab1f27fba8fa1e414813df4e86bdde8-page-0-blog-entry-73-1.jpg

I used this table (http://oregonstate.edu/instruct/exss323/CM_Lab/bsp_deleva.htm) to get the percentage values of a typical person’s body parts (that way I did not need the total mass). Doing so, I obtain the following plot:

i-46c675949785540a9fe6b2f540343a35-page-0-blog-entry-73-2.jpg

Where I have fit a quadratic function to the center of mass plot. Relating this fit to the kinematics equation:

i-6a19e3b981f7689baa5b2ada70a275fa-page-0-blog-entry-73-3.jpg

so, the A value in the fit is 1/2 times the acceleration. This means that the acceleration (in the y-direction) is twice the A value for an acceleration of -11.6 m/s2. Yes, I know this is not what would be expected (the expected value of -9.8 m/s2), but I think it is ok.

  • First, you will see that the data fits a
    parabola very well (the listed RMSE of 0.015 – this
    is root mean square error – 0 would be a perfect
    fit).
  • Next, why would this be off? I calibrated my
    data from the poor quality video using the height
    of Kobe Bryant as 1.98 meters (as listed on
    wikipedia). He was never standing up nice and
    straight except when his arms were over his head
    (making it difficult to see his head). So, this
    could be a cause for the different
    acceleration.
  • Lastly, I really guessed about the location and
    percentage of mass for Kobe’s body parts.

Also, I looked at his horizontal positions (and did the same thing as above)

i-924e151582e071e957bda25b3168fd7d-page-0-blog-entry-73-4.jpg

Here you can see that his horizontal motion is fairly constant (for his center of mass). This is what you would expect for a jump. There is no force in the horizontal direction (while in the air) so there should be no horizontal acceleration. Notice that the motions of the body parts CAN have acceleration, but as a whole, no.

As a comparison, I did another analysis of a jumper – but this jumper used a trampoline. This is video of some world-record trampoline dunk.

Notice that this quality is even worse than the Kobe video (but they do give a nice sideways view – thank you Japanese show people. Here is the data for the horizontal and vertical motions:

i-ee32f229fd0be2bc30561aa39ec3b413-page-0-blog-entry-73-5.jpg
i-2735ae580b037b32741ec6b1cfcc6c84-page-0-blog-entry-73-6-1.jpg

First, note that this analysis shows a vertical acceleration of -6.76 m/s2 with a much higher RMSE (and with much poorer quality video). The horizontal motion shows constant velocity (as expected).

Conclusion: The jump seems real. He is a professional basketball player, so one would expect that he can jump. I am sure I have seen some other video of a person jumping over a moving car, so not an impossible stunt (though still impressive).

Next, was some there some sort of trickery involved? First, let me look at the car. Doing an analysis for the motion of the car (just in the horizontal direction although it is clear it is going down hill).

i-4e041caea77dc1998808f1e7cef5a7f1-page-0-blog-entry-73-7.jpg

Here is the plot of the position of the car. You can see that it is moving at a fairly constant velocity (9.79 m/s or about 22 mph). The question I originally thought of “was it turning around him or something”. This doesn’t say for sure, but I would think it would have a non-constant velocity in this case.

Did the camera play some type of perspective trick? Here is an image of two frames overlapping:

i-6891156d7f63c9956b2fb3a194be7342-page-0-blog-entry-73-8.jpg

This shows Kobe and where he was standing and how that compares to the position of the car at a later time. From this it looks like he was standing very near to the front right tire of the car (clearly not in the middle). This suggests that perhaps there was trickery involved. It really would be foolish of him to jump over a car without trickery. What if he missed by just a little and injured himself – that would not be good for his basketball career, would it?

In my opinion (for what its worth), Kobe has the ability to jump over a moving car. I am not sure if trickery was involved.

Note: If this post analysis looks familiar, it is because I had originally posted this on my old set up. I am moving it to my wordpress install.

Comments

  1. #1 August Larson
    January 29, 2009

    I’m thinking that they created the video by recording Kobe and his jump as Video A and the Aston Martin driving as Video B. Once these 2 were completed, they just layered the two together and that produced the given video. It makes sense because the camera did not move; The perfect way to create this illusion.

    Agree? Disagree?

  2. #2 Rhett
    January 29, 2009

    August,

    That is very possible. I am pretty sure Kobe has the ability to jump over the car, but it would be quite dangerous (especially to his basketball career) if he failed.

  3. #3 Bill
    March 16, 2009

    I agree with August. It is multiple takes layered together. The shadows cast by Kobe and the car seem to be at different angles and if you watch the shadow cast by the goal as the car passes it’s position changes.

  4. #4 Donna
    September 9, 2009

    MSNBC put out a brief article that Kobe admitted the jump was only made possible via “Hoylywood.” Anyway, these guys have contracts about attempting dangerous stunts. Here’s the link.

    http://nbcsports.msnbc.com/id/24071921/

  5. #5 Rhett
    September 9, 2009

    @Donna,

    Thanks for the link. I am not surprised it wasn’t completely real, but I am pretty sure it is possible (if he really tried).

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  8. #8 Priciayana
    December 23, 2010

    Kob is different from others. There is no doubt he used car for showing his talent. It wouldn’t be surprised if he could jump over speeding Aston martin. Even I am confused for that. But an athlete can’t take risk over his career for commercial. If any unwanted thing will happen, then what about his career. He won’t be able to play any more.