What Happens When Two Cars Collide A Science Lesson

Imagine a crash dummy test in slow motion. You see the car accelerating toward the stone wall. Then, in a matter of seconds, you see everything “accordion.” If the car was 12 feet long, within two seconds it may shorten to 9 feet in length. That’s the power of gravity, of objects in motion.

Isaac Newton figured all this out long before the first car rolled off the assembly line. Without gravity, colliding cars would bounce off one another softly like beach balls. With gravity, mass and acceleration combine to pack an enormous wallop.

Force equals mass times acceleration

In an accident, brittle substances like glass and metal instantly transform. The windshield dissolves like an Alka-Seltzer. The solidity of the engine under the hood is so great that it does not accordion. Though these substances have considerable tensile strength, they are no match for the shockwave passing through the automobile, then impacting the occupants of the cab.

Even if the inhabitants are built like Dwayne (The Rock) Johnson, the shock wave envelopes them as if they were ragdolls. Their bodies are whipped against the dashboard, crushing bones.

Energy continues to move through the vehicle. But it has been dissipated by the objects that took the full brunt of impact.

A car collision is like a tidal wave

A car accident is like a mini-tsunami. A wave of tremendous energy engulfs the immediate area, and then moves through everything in its path. At the end of its trajectory, the wave is spent. But it is too late – human beings absorbed too much of the wave’s fury. Their lives, if they are still alive, are changed – in most cases forever.

What’s it all about?

What it’s all about is our slow march toward safer cars and safer driving. As cars, back in the early 20th century, began to achieve higher speed potentials, doctors were staggered by the violence of car crashes.

Car companies set out on a long journey to make automobiles safer – because if injuries are too common, sales will suffer.

Car bumpers, seat belts and safety glass were among the first “anti-gravity devices” car companies came up with. An early insight about seat belts is that they not only protect the body by absorbing violence – they restrain us from flying into one another in the cab, cracking skulls and braking bones.

Airbags followed. Today we are on the brink of a brave new era in driverless automobiles. Yet, even in 2019 that brink may be farther away than we thought. An article published in the New York Times in July 2019 carried the headline, Despite High Hopes, Self-Driving Cars Are ‘Way in the Future’. The article goes on to note that even though hopes were high and ambition even higher, it will likely be many more years before self-driving becomes commonplace. The car companies have concluded that “making autonomous vehicles is going to be harder, slower and costlier than they thought.” (Source: https://www.nytimes.com/2019/07/17/business/self-driving-autonomous-cars.html)

So, error-prone humans are still going to be holding the wheel for many years to come. And even in Elon Musk’s wildest imagination we’re pretty sure there’s no cure for gravity, unless we restrict our driving to the lunar surface. But safety improvements to roads that change the way cars collide, and more important – changing the way we drive our cars – we will stop being vulnerable dummies, and the rate of serious injuries will shrink to a dot.