# Physics in Iron Man 3

One of the more interesting action sequences of Iron Man 3 involves the superhero’s catching of 13 people who have been blown off of Air Force One. He flies around and manages to get 12 of them. He can’t hold on to them all, so he has them hold on to each other, creating a giant chain. He hasn’t gotten the last guy. His computer announces that there are but 400 feet to go before they hit the earth. So he speeds up, grabs the last guy, and slows just in time to miss the surface of the ocean. The crowd goes wild!

The Iron Man films really bug me when it comes to physics. Of all the superhero films, I think they are the worst. And it is all the same problem: acceleration! It doesn’t matter if you are in a bunch of padding or an iron suit, if you decelerate too quickly, you will die. And this happens again and again and again in the Iron Man movies. I know: I’m being a pedant. What’s more, this is far from the only physics related problem in the films. But it is the one thing I just can’t suspend disbelief on. Classical mechanics is the one subject in graduate school that I studied far beyond what was required—because I loved it so much.

So let’s look at our little sky dive sequence. I’m going to keep this really simple because I figure it will be bad enough for those who are not freaks about this stuff like I am. Iron Man is at 400 feet. The man he needs to catch is further down, but I’m not even going to worry about that. We’ll just assume that Iron Man catches him at that point. Now the man is falling at terminal velocity which is roughly 120 mph. That’s 55 m/s at a height of 120 m. But iron man can’t be moving at that speed; if he were, he would never catch the guy. So I’m going to assume he is moving at twice that speed: 110 m/s.

Thus, if he keeps at that speed for one second, they crash. So there isn’t much time. Over the course of 120 m (d), Iron Man must decelerate from 110 m/s (v0) to 0 m/s (vf). And we want to know what the average acceleration (a) is for these 13 people. Luckily, there is a handy equation that people learn in the first week or two of physics that helps us out:

vf2 = v02 + 2 * a * d

The answer is that the average acceleration is 46 m/s/s or a tad less than 5 gs. This is about the level at which people lose consciousness. But there is a bigger problem here. I call it the Eraser factor.

I learned about this from my friend Mikhail. In Eraser, Arnold Schwarzenegger falls out of a plane and moves through the sky. He is looking for a parachute that also fell out of the plane. He grabs it and then fights to put it on, buckles it up, and pulls the rip cord. I asked Mikhail if this was possible. But I only mentioned the getting to the parachute part because frankly that was the impressive part for me. He told me it was, but that there was a problem. After locating the pack, you would have to “fight to put it on and buckle in.” Why? Because no one is strong enough to hold on to the parachute when it opens.

So think of our Air Force One survivors. Imagine a 150 pound man hanging from a pull-up bar. Now imagine what would happen if you suddenly attached 750 pounds of weight to him. He’d lose his grip and fall. As they all would. And this would happen at the beginning of Iron Man’s deceleration. So they would likely hit the ocean at a lot faster a speed than if Iron Man had never caught them in the first place. This reminds me of the film Hancock, where all of that superhero’s efforts to help people caused bigger problems. But the makers of Iron Man 3 just didn’t realize it.

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