Note: This is part of my ongoing attack of ESPN’s show Sport Science. Really, I am continuing to look at the episode where they calculate a football player can produce 57,000 Watts by pulling some stuff. Wait…I don’t want to limit my stuff to Sport Science. I see this stuff all the time. The problem is that people confuse the force needed to move something with its weight.

So, you want me to pull something? Great, I am a physics guy. I could probably pull maybe 100 pounds. That seems reasonable? But wait! I will increase it to 500 pounds! That is like two huge football players. Pulled by me! No, I will crank it up. 1000 pounds! 3000 pounds! How about OVER 3500 POUNDS! I am going to try it. Here it is:

That is not a fake video. It is real. I pulled a Mazda 5 with some kids and a grown woman inside.

Now on to the real stuff. Yes, it is true. I did not exert a force of 3500 pounds. Here is a force diagram for the car.

So let me pretend like I want to pull the car at a constant speed. In this case, I would have to pull with a tension equal in magnitude to the frictional force – not equal to the weight of the car. Sure, often the frictional force is related to the weight. However, just because the weight is large this does not mean the frictional force is too large. What if I want to get it moving? In this case, I just need to pull a little harder than friction and the car will accelerate. Really, it is not that hard. Here is my 6 year-old daughter moving the car (she had trouble pulling it the whole 5-yards, so I won’t use her for the calculations below). Also note: it looks like the driveway is at an incline – that is because of the camera. This is Louisiana, everything is pretty much flat.

### Calculating the power – the wrong way

I still never figured out how Sport Science calculated a power of 57,000 Watts. My guess was that they assumed the force was the weight of the tires and the sled (which it wouldn’t be). This still gave me a value that was too small. Anyway, I am going to calculate my power doing it **the wrong way** and see what I get. Here is what I am starting with:

- I pulled a Mazda 5 – weight of about 3500 lbs (11,000 Newtons)
- The distance the car was pulled was 5 yards (4.6 meters) – just like in the Sport Science
- The time it took me to go 5 yards was about 9 seconds.

Using my same calculations as before and the weight of the car as the force, I get:

I failed to get the 57,000 watts, but I am better than an elite bike sprinter (2000 watts).

### The correct way

If I wanted to do this the correct way, I would need to measure the force I exert on the car (which is NOT the weight). I did not measure this, but I am sure my actual power is significantly less than 5000 watts.