Saturday Entertainment: Rocket Sled Vs. Car

One of the more amusing claims I kept reading and hearing about the collapse of the World Trade Center back in 2001 was about how the "physics didn't add up", or some such phrase to indicate that what happened didn't make sense. I thought this was so much twaddle at the time, and said so. Of course, that meant I was a naive dupe of the New World Order, but I digress.

The important thing to remember here is that what we should have learned from 9/11 is that when particular things composed of particular materials come together at speeds and in ways we haven't experienced before, it's anyone's guess what will happen. What "physics" apply in a particular situation are often very different from what we assume will apply.

The show Mythbusters provides lessons in this sort of thing quite often. In it, they test some urban legend, bit of folklore, or seemingly outrageous claim to see if it makes sense. Whether the question is if a Saint Bernard bringing you a shot of cognac when you're trapped in a snowdrift is a good thing, or how plausible an anti-Gorn cannon is, they use science and mechanical abilities to see what might be true. Often, they do this by destroying something in pretty spectacular fashion.

Yes, I really like the show. It's one of the few things I miss about cable television.

This particular segment from Mythbusters features a rocket slide slamming into a car at 500 miles per hour, or thereabouts. The episode's premise was to test a claim that a snowplow had once cut a small imported car in two. The Mythbusters had already tried this out, and found that, sure enough, it wasn't possible. I think enough of us have seen auto accidents to visualize what would happen. We're used to what happens when steel vehicles collide at, say, 20 to 100 miles per hour. But, this being Mythbusters, they wondered if it was possible at any speed.

So, they hired a place with a rocket sled track to set up an experiment. Here it is:

The reason this episode reminded me of 9/11 is the speed with which the sled hit the car, and how this was outside the experience of all the testers. Both they and I made guesses about what would happen. Mine was that the engine would be either crushed or splintered, and the rest of the car more or less cut in two. Watch the video to see the Mythbusters' guesses. I'm an engineer with some experience with cars and aircraft. The people in the episode were experienced at destroying, working with, and building quite a few mechanical devices. None of us, though, is a materials scientist or an expert in the technologies and metals involved in car manufacturing. None of us was right, really. Those points are related.

So, just like we'd never seen anything like an airliner loaded with fuel hitting a skyscraper with a steel external structure at more than 350 miles per hour, this experiment had a result few laymen, if any, would have guessed correctly. As NASA demonstrated during the Columbia accident investigation, even the experts can be wrong sometimes. They didn't think the foam that covered the main tank could damage the Shuttle if it broke off in a launch, but it turns out that's exactly what happened. That's why talking about how the physics don't add up in a new situation like this is nonsense.

Enjoy the explosions.