Dot Physics

18,000 lbs of cumulative force

I want to give ESPN’s Sport Science another chance. The segment on Tim Tebow didn’t really have any errors. I thought, cool – what about this one on Jason Pierre-Paul? Here is the clip. Oh wait, embedding is disabled. Ok – if you want to watch go here (the image is a link)

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The goal of this segment was to examine why Jason is so awesome at tackling. The answer: because he can do flips. Really, that was the answer. Let me briefly go over some of the problems with this segment.

Correlation does not mean causation

They didn’t say it explicitly, but it seems the are saying the reason he can tackle so well is because he can do “back flips”. NOTE: those are back handsprings, typically (according to my daughter) if you say back flip, you probably mean a back-tuck and your hands don’t touch the ground. This is a back flip:

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Anyway, Sport Science has already shown that they don’t understand correlation. So, the last thing to say – xkcd has the best response to “correlation implies causation”.

Other claims

While doing the back handsprings, Sport Science says the following:

  • Jason rotates around his center of mass at 11 mph
  • Feet and hands sustain forces up to 3 times his body weight – (over 800 lbs)
  • He can do this 23 times in a row – that is cyclic loading (whatever that means) of 18,000 lbs of cumulative force (in less than half a minute)
  • His body absorbs more weight than the entire roster of the New Orleans Saints (Go Saints)

So, which of these claims are ok and which are crazy? The 11 mph seems like it would be easy to verify – even though the problem is not really defined. I guess they meant that his feet are moving 11 mph? They should have instead talked about his angular speed. Also, I could do the force exerted on the body during the “spring” part of the handspring. It could easily be over 800 lbs. But you know what I am going to talk about, don’t you?

Why do they make this stuff up? Oh, if you push with 800 lbs for 23 times – that is THE SAME AS LIFTING ALL THE NEW ORLEANS SAINTS! I know, they didn’t say he could lift the Saints, but it kind of implies that – doesn’t it? Let me first point out that Sport Science first claimed that Jason pushed with 800 lbs both with his feet and hands. If he does 23 hand springs, (by their methods) that would be 23*2*800 = over 36,000 lbs.

Next, a thought demo. Let me assume that all the Saints have a weight of 18,000 lbs. Let me also assume that when I run, my foot hits the ground with a maximum force of 1.5 times my body weight (really, this is a silly thing to say since it is not just the peak force – but I will use their silly method). Also, suppose that with each step, I move 4 feet. So, how many steps would I have to take to have a “cumulative force” equal to the weight of all the Saints? Just 75 steps or running just 300 feet. I can do that.

Seriously, what does this have to do with tackling? Sport Science – you should stick to reproducing Kobe Bryant’s fake jump over a car. You did a pretty good job at that.

Comments

  1. #1 Anonymous Coward
    April 22, 2010

    Re: “His body absorbs more weight than the entire roster of the New Orleans Saints”

    I didn’t watch the show, but I love the “scientificy” expression “absorbs more weight than…”! It makes Jason Pierre-Paul sound like he’s starring in an advertisement for paper towels.