Physics of car accidents.
In this article we will discuss how safe are cars now? Why not make the car even more durable, and what did the engineers work on to prevent the dire consequences of an accident?
A liter of gasoline contains about 56 megajoules of chemical energy. This is more than in the explosion of the same amount of TNT. And this energy would be enough for a whole day of toaster operation. Cars work by burning gasoline, which converts chemical energy into kinetic energy, helping the car move. Eighty percent of the energy is lost as heat in the engine, but 20 percent of 56 million joules is still a lot. It takes only 5 teaspoons of gasoline to accelerate a 2-ton car from 0 to 60 km / h. It 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, dropped from the third floor. For the car to stop, all this energy must go somewhere. If the brakes stop the car, they dissipate energy by heating (and then cooling) the brake pads and discs. And in the event of a collision, the energy is dissipated by the deformation of the front of the car. And since stopping slowly is better than stopping quickly, cars are carefully designed to crumple in a collision. This lengthens the collision time and requires less braking acceleration to stop.
Large breaking acceleration has a very bad effect on human brains and organs. But people don't really like driving cars with a long front. Most vehicles have 50 cm of crumple space in which they must dissipate the energy equivalent. The deformation of the front of the vehicle must be able to withstand a force equal to a quarter of the thrust of the shuttle's main engine. More than half of the controlled crush must be taken up by a pair of steel bars connecting the main body of the car to the bumper, which flex and deform to absorb energy and slow the car down. Any remaining energy must be absorbed by the deformation of the rest of the metal in front of the car. This planned destruction allows the vehicle to decelerate quickly, but at an acceptable and consistent speed.
If the cars were very solid, they would stop so quickly that the acceleration in them would be 15 or more times higher than that experienced by cosmonauts in training. Such huge overloads are incompatible with life. Engineers have learned how to make cars with crushing parts that create a safe zone inside. Fully solid cars are not suitable for the safety of the driver and passengers. In completely solid cars, even in a collision at a very low speed (30 - 40 km / h), people could die.
Driving and being passengers in cars is a part of our everyday life. We are sure that there are a lot of people who are thinking about possible car accidents, but still use cars every day. The vehicles occupy such a big part of our lives that we can even have dreams about car accidents. Have you ever had a car crash dream?
