Hat tip to Derek for pointing out the following ESPN Sport Science video. While you watch it, see if you can grade it. What mistakes are made?
Note: You know, I am not a big Sports Science fan, right? Just to get that out in the open. Now, let the grading begin. These are the errors that I found - either flat out wrong or extremely misleading.
Maybe I am being picky, but Sport Science claims that in a helmet-to-helmet collision a player can experience "100 g's of force".
Is that wrong? Yes. The unit "g's" is a unit of acceleration. Well, g's isn't really acceleration. It is the acceleration relative to free fall (as described by Wikipedia). I guess you could call it the apparent weight of acceleration. If you are standing still on a floor at rest, then you would be a 1 g. However, your acceleration would be zero. All in all, not the best unit for acceleration.
Now, often this will be called the "g-force". But it is not a force. Sport Science should know that. If they don't know that, they could just look it up on Wikipedia, pretty simple to do. What should they have said? They should have said a head (not the whole body) can have an acceleration of up to 100 g's. That would be good enough. As an example, think about two heads. A normal head and a giant head that has a mass 10 times as much. In order for these two heads to have the same acceleration, the giant head would have to have 10 times the force on it in the same amount of time. So, force is not a good thing to use here.
Right after this, Sport Science said it again. They said "on special teams, players can experience 190 g's of force". Should I take off twice for the same mistake? I guess so.
Talking about collision between two players, Sport Science shows this:
Here are the words that go along with that:
Again, you could possibly give Sport Science the benefit of the doubt here. You could make this seem right. Maybe they mean that the change in speed of one player's head is 14 mph. Ah ha! But they didn't say that. They said deceleration (I hate that word). Well, what is the difference? Here is the vector definition of average acceleration:
So, if I go from 20 mph to 6 mph the change in speed could be 14 mph. What if this takes an hour? What if this takes a nanosecond? Both have the same change in speed, but different accelerations. And for that matter, I am not sure where the 14 mph change in speed comes from. Was the running guy going 20 mph and then slowed down to 6 mph? Also, 20 mph seems a tad bit high for the speed of a football player, but what do I know?
I am pretty sure they are talking this red player having a change in speed of 14 mph. It seems their set up had two guys going towards each other at 10 mph each.
Let's say they are both going 10 mph, then they stick together going 6 mph to the left. Here is a before and after diagram.
Could momentum be conserved here? Sure, if the two players were different masses. Also, they didn't say that the two players were moving at the same speed. They just said that the collision speed was 20 mph. Anyway, in this case, the red player goes from an x-velocity of +10 to -6 mph. This would be a change in speed of -6 mph - 10 mph = -16 mph. Oh, this is just unclear. They could have meant any number of things. I suspect they wanted to say that the red guy went from 20 to 6 mph. However, the video clearly shows that he went in the other direction. Direction matters when you are dealing with vectors.
Collisions are tough. What is important in a collision? Energy? Change in momentum? Acceleration of the object? I think the general rule of thumb is to characterize collisions by the acceleration the object has. So, what about a sledge hammer? If you just say "sledge hammer" you really aren't saying much. The results of getting hit with a sledge hammer depend on the situation. The same is true for collisions between two football players. I guess you could also say getting hit by another player is like getting hit by a canary bird (especially if the bird was quite large and moving at super sonic speeds).
So, I guess this isn't really wrong as much it is pointless. Should I take off points for this? I am going to, here is why. This is Sport Science for goodness sakes. I expect more out of them.
Again, I guess my complaint is the pointlessness of this comparison. Yes, 40g's is greater than 7 g's. However, the time is also different. If I jump off my desk and land on the floor, I can experience quite a large acceleration (depending on how I ben my legs). This acceleration can be several times greater than the acceleration of an F-16 pilot even. Oh, I know I am just getting cranky. This is what Sport Science does to me. Not my fault.
Dear Sport Science. Here is your short episode back. Sorry about all the red ink and the coffee (I spilled a little bit on your episode while grading). Your grade for this assignment is a D. I hope you take these things seriously. Lots of people actually watch your stuff and look up to you. Please try a little bit harder.
P.S. Batman has The Joker, Harry Potter has Voldemort, and I have Sport Science. Bring on your next move.
