I would like to continue my attack on the show Sport Science – ESPN. In this short episode, they are comparing the power of NFL player Marshawn Lynch with that of a truck. You can watch it here if you would like.
There are two things that are not quite right with this episode, first, the power thing. I will save the friction problem for another post. So, if you didn’t watch that clip, the basic idea is that Marshawn pulls some heavy tires. Sport Science then calculates the power needed to do this and then repeats a similar thing for a truck. Quick review. What is power? In short, power tells you how fast you can either do some work or change your energy.
For the case of someone pulling something, I assume that the power would be based on the work this person does. Let me keep it simple. If you are pulling something in the same direction the object is moving (at a constant speed), the work done is:
Fairly straight forward, right? Sport Science puts some motion sensors all over Marshawn’s body. They say this is so they calculate the power, but it looks like it is just to make this animated skeleton move like him.
What actually is known about Marshwan pulling stuff?
- He pulls some tires and a sled with a weight of 585 lbs (2600 Newtons)
- The sled is pulled 5 yards (4.6 meters)
- Not exactly sure about the time this takes (because they made part if it in slow motion) but I would guess it is somewhere between 5 and 11 seconds. I counted 11 in the actual clip.
- Sport Science claims that Marshawn produces 573 Watts per kg. (this was in the online clip)
However – there is a difference in the version that was on TV. I thought I was crazy because I didn’t see this in the online version. Good thing I had taken a picture of it. Check this out.
Yes, that says Marshawn produces 57,000 watts. They even went on and showed how many TV’s that could run. How did they get such a high number? My first thought was that they were just taking the weight of the tires times the distance for the work. This would be a pretty large error (that I will discuss in another post), but let me just assume this is what they did. How much work would it take to “lift” 585 pounds 5 yards?
If I let the time be 5 seconds to pull this thing (which I pretty sure it was actually longer than that), then the power would be:
Hmmmm….How can I make this work? In case you didn’t realize, 2300 watts is not quite 57,000 watts. Let me approach this from a different angle. What am I pretty sure about? I am pretty sure about the time and the distance. Let me calculate what force would be needed (what force Marshawn would have to pull with) to get that power (assuming 5 seconds, which I think is low).
So, for a power of 57,000 Watts pulling something 5 yards in 5 seconds you would need a force of 62,000 Newtons (14,000 lbs). Hmmm. I am sure Marshawn is a powerful dude – but 14,000 lbs? There is something wrong.
According to Wikipedia’s page on human powered transportation, an elite sprinting cyclist can produce 2000 watts for very short times. I am sure Marshawn is elite, but not 20 times more elite in terms of power output. Something has to be wrong.
Maybe the people at ESPN were thinking: “hey attach some sensors to this guy and determine his power. Oh, just put down something huge like 57,000 watts. No one will ever check that, it will be fine.”
PS Thanks to Nick at The First Excited State for pointing out the pure awesomeness of Sport Science.