Tuesday, November 29, 2011

Can Kobe Bryant jump over a moving car?

In 2008, a commercial promoting the new "Hyperdunk" line of basketball shoes went viral on the internet. The commercial involved Los Angeles Laker, Kobe Bryant, jumping over a moving Aston martin.

"If 'Rambo Part XX' can be a one-man militia, I can jump over an Aston Martin" he told the Los Angeles Times.

Understandably, there was a lot of speculation as to whether or not the stunt was real. Can we use physics to determine the validity of the stunt?

The "Dot Physics" blog of Wired website used physics to examine whether or not the jump was fake. They used Tracker Video Analysis to get the x,y positions of each body part in each gram and plotted center of mass values against time. They then fit a quadratic function to the center of mass and related it to the kinematics equation and found that the data fit the expected parabola very well.

Next, they examined Kobe's horizontal position during the jump using the same method. They found that the horizontal motion of his center of mass was fairly constant, which is what one would expect for a jump. There is no force in the horizontal direction while in the air, so there should be no horizontal acceleration.

Thus, by examining his vertical and horizontal positions, it seems as though the jump itself was real. However, an image overlapping two frames shows that Kobe was actually standing very near to the front right tire of the car, not in the middle of the car. This suggest that a degree of deception was involved.

"Sports Science," which is an ESPN television series that explores the science and engineering underlying athletic endeavors, also examined whether the stunt was real or fake. They, however, took a different approach: they tried to recreate the stunt that Kobe apparently performed.

The stuntman must perform the very difficult task of perfectly synchronizing the peak of his jump with the top of the car passing underneath him. In order to clear the car, a jump of at least 48 inches off the ground is required. The stuntman himself can jump 52 inches off the ground. If the Aston Martin is travelling at 55 mph it moves 1 foot every 0.01 seconds, meaning the stuntman must leave the ground when the car is exactly 24 feet away. However, it takes the brain 0.25 seconds to react to visual stimuli, meaning the stuntman must decide to jump when the car is actually 44 feet away.

After many many trials, they were ultimately unable to recreate the stunt. The stuntman was able to jump a high enough height to clear the car but the timing was impossible - 0.01s accuracy was required. The only time they were able to recreate the stunt was when the stuntman wore a harness connected to a 40 foot crane in order to give him an extra boost and to keep him safe.

Thus, the stunt was fake.

Furthermore, the earlier mentioned Dot Physics blog found that the Aston Martin that Kobe apparently jumped over was travelling at a constant velocity of about 22 mph. If Sports Science could not perform the stunt when the car was travelling at 55 mph, it is even less likely that Kobe was able to perform the stunt when the car was travelling at 22 mph since the slower velocity of the car means that Kobe had to be in the air for a longer amount of time.

In conclusion although the jump itself was real, the stunt was faked in some way.

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