image from http://turbocharged64.wordpress.com/
So, Bob and I were sitting with our friend Jeff at a Seattle pub, after a long and trying city day a couple weeks ago.
We got onto the subject of traffic accidents, since that morning Bob and I had encountered a car driving straight towards us, in our lane, at freeway speed, before it swerved over to the shoulder (on our right) and rushed past us. Unnerving, to say the least.
Jeff declared that if you’re in a car going 60 mph, and you run head-on into another car which is travelling towards you at 60 mph, it’s no different for your car than it would be if you ran into a stationary wall. The principle being that in either case, your vehicle abruptly switches from 60 mph to 0 mph. So it doesn’t matter whether the thing you hit is travelling toward you, or is standing still. You come to an abrupt stop just the same.
I contend that it does matter. I believe the impact of two vehicles in motion would be greater, so that if you’re going 60 mph headed east, and you crash into a car headed west at 60 mph, that the impact is going to be greater than just if you hit a stationary object.
I know that cars crinkle inwards upon impact, softening the blow, but I want to ignore that variable. I also know that the answer has something to do with the weight of the respective objects in motion, and with their ability to recoil, but I’m not sure how that all works.
In my (admittedly brief) efforts to dig up an answer, I discovered that Google Sketchup now has a Sketchy Physics program, where you can create and manipulate objects and they will behave according to the laws of physics. Since it’s glorious clear sunlight and 75 degrees outside today, I won’t be able to fuss with the finickiness of Sketchup right now.
( Last time I played with Sketchup, it had the dual qualities of being really addictive and being kind of opaque to the new user. I kept getting results that were just tantalizing enough to keep me trying to master the commands, until I realized how many hours I was sinking into it and removed it altogether from my computer.)
Actually, I’ve just discovered that devotees of Physics Sketchup have posted some of their animations on YouTube, although I haven’t found any that exactly fit my problem. Here’s one of a pickup truck which is shown spilling cans out of the back of it as it goes spinning over extreme terrain. Computers bring out the finest flowering of the fertile geeky mind.
Any of you out in cyber land who want to post a comment that would shed some light on this, please do so!
4 Comments
Lovely to ‘meet’ another Rowan mom
A brick wall doesn’t have initial velocity or force from it. The only force enacted upon impact is the automobile exerting force on the wall. Assuming the wall stays upright, that force is pushed back onto the automobile from the wall.
A car of the same mass going toward you at the same speed is double the impact force of one car hitting a brick wall because that car does put force onto the second car. That’s assuming that both cars are equal mass. If the second car is more mass than the first car, then the first car will receive more damage than hitting the brick wall at twice the speed.
I posted in your Etsy thread, not sure if you saw it or not. The answer depends on a lot of things and it’s not definitively yes or no.
There are many variables, including the mass of the objects, their instantaneous acceleration, the rigidity of the wall, angular momentum…If you wanted to model it, it gets complicated quickly by the integral of the acceleration.
I’m so pleased to have two answers offered here! It seems like Jadewick’s explanation more or less agrees with my initial hunch. I love the luxury of having people offer me tidbits of knowledge; it’s like being handed a virtual bon-bon!