# That’s why in a frontal collision the speed of the cars does not add up

## If two cars are moving simultaneously at the speed of 100 km per hour to meet each other and occurs a head-on collision, the first day of speed at the moment of impact?

Among motorists runs a lot of plausible myths in which they believe a large number of people. About the many myths we have already written on the pages of our publication. Today we want to talk about the most common myth about the folding speeds of two cars in a frontal collision. Let’s dispel this myth once and for all.

Once it so happened that many people believe that if two cars collide head-on, the impact energy will correspond to the double speed of both cars. That is, as suggested by many motorists, to understand what powers would be frontal impact, you need to add up the speeds of both involved in an accident car.

To understand that this is a myth, and to calculate the force of a frontal impact and the impact of vehicles involved in such accident, you need to make the following comparison.

So, let’s compare the effects of vehicles in different accidents. For example, each car moving towards each other at a speed of 100 km/h, and they then faced head-on with each other. Do you think the consequences of a frontal impact will be more serious than hitting a brick wall at the same speed? If based on a widespread myth, which for several decades walks among the people who only half know the physics (or not at all familiar with it), at first glance, the consequences of a frontal impact of two cars at 100 km/h will be worse than if you hit the car at the same speed on a brick wall, as supposedly the force of a frontal impact will be greater due to the fact that the speed of cars in this case, you need to lay down. But it’s not.

In fact, the force of a frontal impact of two cars at 100 km/h will correspond to the same force that upon impact at the speed of 100 km/h into a brick wall. This can be explained in two ways. One simple one that will be understandable even to a schoolboy. The second is more difficult, which not everyone will understand.

## SIMPLE ANSWER

Indeed, the total energy that must be dissipated through crushing of the metal body, twice in the collision of two cars head-on, rather than when you hit one car on the brick wall. But in a frontal collision increasing the distance of the crumpling of the metal bodies of both machines.

Because bending metal is the place where there is all this kinetic energy, the collision of two cars head-on energy will be absorbed twice as it will be absorbed by two cars, unlike hitting a brick wall, where the kinetic energy will be absorbed by one machine.

Thus, the deceleration speed and the force of a frontal impact at speeds of 100 km/h will be approximately the same as when hitting 100 km/h in a stationary brick wall. Therefore, the impact of two cars moving with the same speed and colliding head-on will be approximately the same as if one car at the same speed crashed into a stationary wall.

## A MORE COMPLICATED ANSWER

Suppose that the cars have the same mass, the same characteristics of deformation and is at a right angle to face head-on and not fly off from each other far away. Assume that both cars will stop at the point of collision. Thus, moving, for example, with a speed of 100 km/h, each car stops upon impact with 100 to 0 km/h. In this case, each car will behave exactly the same as if each of them collided with a stationary wall at a speed of 100 km/h. In the end both car will get the perfect when a frontal impact is the same damage as when hitting the wall.

To understand why the same damage, you need to conduct a thought experiment. To do this, imagine two cars traveling at the speed of 100 km/hour towards each other. But on the road between them is thick, very strong and solid wall. Now imagine that both cars simultaneously slam into that imaginary wall from opposite sides. Every at this moment at the same time stops from 100 km/h to 0 km/h. Since the wall on the road very strong, it does not transmit impact energy of one car to another. The result is that the two cars hit in separate standing wall without exerting influence on each other.

Now repeat this thought experiment with more subtle and not very strong wall, but is able to survive under attack. In this case, if the strike simultaneously from two sides, the wall will remain standing in place. Now imagine instead of a wall sheet of a solid piece of rubber. As two cars crash into him at the same time, the rubber sheet will remain in place because both cars will hold the rubber in one place at the time of simultaneous impact. But a thin sheet of rubber could not affect the slowing down of any machine, so even if you remove the rubber sheet between the cars that collide head-on, each car is still at the moment of impact will stop from 100 km/h to 0 km/hour, that is exactly the same as if one car crashed into a strong stationary wall at a speed of 100 km/h.

## The same impact energy and impact at collision with standing vehicle or stationary wall?

This is another common myth among motorists, which is that if at speed, for example, 100 km/h to collide with a standing car, the force of the blow will be exactly the same as if a car at speed of 100 km/h flew into a stationary wall. But this is not so. This is pure myth, based on ignorance of basic physics.

So, let’s imagine a situation in which one car moves at a speed of 100 km/h and at full speed collides with the exact same car parked on the road. At the moment of impact one car, continuing its movement, will push the other car. In the end both machines will fly away from the collision. At the moment of impact the kinetic energy will be absorbed by body deformation both cars. That is, the impact energy will share between the two cars. In the case of hit a fixed wall of the vehicle at speeds of 100 km/h body deformation will be only one car. Accordingly, the force of the blow and its consequences for the machine will be higher than when struck at the speed of one car to another, which is in place.