The Forces of Life

I was rewatching the second Matrix movie a while ago and got to that really pumped-up car chase - you know, the one with the truck that smashes into all the cars and all the Michael Bay-esque explosions? I remember watching and wondering why the car looked like it had recently been attacked by chainsaw-wielding lunatics while the truck barely had a scratched-up paintjob. A couple of years later - because I'm really not that big of a fan of the Matrix series, the last time I watched it, I was around 12 - I learned about the forces that occur in a car crash.

It turns out that both the car and the truck experience the same amount of force, but the car is lighter, so it moves further. The force exerted by a vehicle in a car crash is influenced by two things - the mass of the vehicle and its speed at the time of the crash. The car weighs around 1300 kg while the truck weighs nearer 13,000 kg, but they both experience the same amount of force - doesn't make much sense, does it? Well, it turns out, the force that each of the vehicles experience is a combination of the force exerted by each individual vehicle. 

Every time the truck smashes into the car, the producer spends another large sum of money on VFX. The other thing that happens when the two vehicles collide is that the car moves a lot further than the truck does. This made sense to me - the truck's a lot heavier than the car, so obviously, it won't move as far. 

What really struck me then, though, was the difference in the degree of damage done to each of the vehicles. Since then, due to my extensive (HA! If you believe that, there's a bridge I can sell you in New York) research into the manufacture of cars, I have found that this is intentional. Car manufacturers intentionally use a combination of stiff and soft materials to make sure that if you're in a crash, your bonnet will crumple. They do this so that they can make more money off of repairs. No, not really, of course. The hood of your car is what is known to the car-manufacturing biz as a "crumple zone". It's meant to take the impact of a crash so that you, the driver/passenger/annoying, hyperactive kid in the back don't have to. Older cars didn't have a crumple zone, so if you smashed into a truck in a car in the 1940s, you were a lot more likely to end up stretched across the sidewalk than you are today.

Trucks, on the other hand, have much higher chassis than cars do, because their wheels are larger. The lower part of the truck's body is usually what plows into the car, and it's quite rigid. The truck is also much heavier than the car, so it's less likely to fall off the road into a ditch when it bounces back and explode in a massive, Hollywood-style mushroom cloud. That's why the truck doesn't seem to be nearly as damaged as the car.

Thinking this through, though, I realised that a large part of the reason I understand this stuff is because I actually paid a modicum of attention in my ICSE physics classes. After all these years of complaining about how terrible it is, this post is something of an olive branch to the ICSE board and to my teachers, and a thanks for all the stuff they've taught me over the course of ten years.