Physics of car accidents

In this article, let’s discuss how safe cars are now? Why not make cars even more durable, and what have engineers worked on to prevent dire consequences in an accident?

A liter of gasoline contains about 56 megajoules of chemical energy. That’s more than the same amount of TNT would have detonated. And that energy would be enough to run a toaster for a whole day. Cars work by burning gasoline, which turns chemical energy into kinetic energy, helping to move the car. Eighty percent of the energy is lost as heat in the engine, but 20 percent of the 56 million joules is still a lot. It only takes 5 teaspoons of gasoline to accelerate a two-ton car from 0 to 60 km/h. That doesn’t seem like a lot of fuel, but the energy of a car traveling at 60 km/h is comparable to that of an elephant or rather a stegosaurus thrown from the third floor. For a car to stop, all that energy has to go somewhere. If the brakes stop the car, they dissipate the energy by heating (and then cooling) the brake pads and discs. And in the event of a collision, the energy is dissipated by deforming the front of the car. And because a slow stop is better than a fast stop, cars are carefully designed to crumple on impact. This prolongs the collision time and stopping requires less braking acceleration.

High acceleration is very bad for human brains and organs. But people don’t really like driving cars with a long front end. Most cars have 50 cm of crumple space in which they have to dissipate the energy equivalent. The deformation of the front of the car has to withstand a force that is equal to a quarter of the thrust of the shuttle’s main engine. More than half of the controlled buckling must take up the pair of steel rails connecting the main part of the car to the bumper, which bend and deform to absorb energy and slow the car down. All of the remaining energy must be absorbed by the deformation of the rest of the metal in front of the car. This planned collapse allows the machine to slow down quickly, but at an acceptable and stable rate.

If the machines were very hard, they would stop so fast that the acceleration in them would be 15 or more times greater than that experienced by astronauts in training. Such enormous overloads are not compatible with life. Engineers learned to make machines with crumpleable parts that created a safe zone inside. Fully solid cars are not suitable for driver and passenger safety. In fully solid cars, even in a collision at a very low speed (30-40 km/h) people could be killed.

Leave a Reply

Your email address will not be published. Required fields are marked *