How is the newer cars are more fragile during an accident but are more safe for the passengers
In: Physics
Imagine someone hit you with a baseball bat or a pool noodle. Both are about the same size. One is soft. One is firm. Which one will hurt you the least? The soft one, even at the same speed.
Think of it like this. If you and a friend are carrying a 12ft beam of steel and your friend drops his end, you’re going to feel a serious amount of vibration in your hands. Now if that’s a 12ft beam of glass and your friend drops his end, it’s going to shatter and you won’t feel a thing.
Similarly, if the front of the car crumples, that means that most of the force is spent on crumpling the car and not crumpling your bones.
So a good car will break the car (acting like glass) and not you (acting like steel).
The energy from a crash needs to go somewhere and destroy something.
It could either destroy the car, or destroy the people.
For obvious reasons, we made the choice to destroy the cars so that the forces acting on people were far less.
Older cars with a “strong” build would make the driver into the crumple zone
Newer cars behave like air cushions, except that they don’t go back to their original form.
This is done to protect people both inside and outside the vehicle. By deforming itself the car dissipates a great deal of energy therefore reducing the impact force exerted on people.
They’re not more fragile, they’re designed to absorb the impact energy rather than transferring that energy to the passengers—better to sacrifice the engine or trunk than a human. However, there is a very strong roll cage surrounding the passenger compartment to prevent the passengers from getting crushed.
If the cars crumple up, it means that it’s absorbing the energy of the impact so the passengers aren’t the ones crumpling up
You could build an incredibly strong car that takes minimal damage in a collision, just uparmor that bad boy like its a tank
Bad news, when you hit something at 60 mph, the meatbags inside will become meatloaf on the dash
Cars aren’t design to preserve themselves, they’re optimized to protect their occupants at the expense of themselves. The difference between a new $40k car having $10k in damage because its robust or being totalled is irrelevant if you don’t have legs anymore so we favor the legs over the reusability of the car.
Keeping people (and other meatbags like pets) safe in a crash is about decelerating slowly. Highway speed is roughly 27 m/s, if you come to a stop in 10 milliseconds you’ll cover 13.5cm and experience 275 Gs. Bad news, 100 Gs for even a short time will generally break your neck. So to get this down to a survivable level, say 50 Gs, you need to decelerate over more time/distance. Seatbelts help with this, they let you decelerate over maybe half a meter and airbags do a good job supporting your head, but if you want a reliably survivable head-on highway impact you need the person to decelerate over 75 cm which means you need the front end to implode to buy you more time and distance
So that’s what it does. The front and the rear of the car both crumple but with a fair amount of force required to greatly extend the time/distance of the impact so the peak force is lower and doesn’t just turn you into mush. The actual passenger compartment is quite strong and rarely will things significantly intrude on it even if the entire front end is basically missing there’s a decent chance some of the doors still work.
While cars have gotten significantly heavier and more expensive with all the safety tech, it really does help. In 1960 fatalities were 5 per 100 Million Vehicle Miles, by 1980 they were down to 3.3, and in 2018 it was just 1.13 fatalities per 100 Million Vehicle Miles.
The energy from a car crash has to go somewhere, and it is safer for it to break the car than break your bones.
It’s the same concept as using water barrels or the front parts of guardrails that are designed to deform/break in order to distribute the force of the impact.
The car itself absorbs the impact and in the process both slows down the passengers and prevents them from being impacted by parts of their own car.
They design them to be. Cars nowadays are designed to destroy themselves to take the brunt of the damage. The thinking (and rightly so) is a human is worth a lot more than a car. Seems kindof simple, but in the 50s and 60s, even though every car designer would have agreed with that sentiment, the knowledge on how to do that simply (so it could be made well but cheaply) and safely just didn’t exist. I mean the solution back then for an uber survivable car before lapbelts then Volvo’s 3 pt seatbelt, then airbags in the 80s would have been to fill the inside of the car with foam or wrap the passengers with bubblewrap.
And not that the concept of crumple zones didn’t exist.. its just it took a lot of experimentation (build and test) on how to fold, bend and cut metal so that when it received a great impact force, it would warp and deform in a way to send the force away from the passengers. With the advent of computer modelling this got a LOT easier to model, thus a lot cheaper. Also more energy absorbing materials (i.e. plastics, foams etc.) became feasible.
The old cars from the 50s and 60s are like giant rigid metal tanks; the most deformable part is the big void in the middle where the squishy humans live. Modern cars, the strongest part of the car is the safety cage with the squish humans – the rest of the car throws itself literally under the bus to sacrifice the humans. Yay car.
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