How is the newer cars are more fragile during an accident but are more safe for the passengers
In: Physics
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.
If you are talking about how cars “crumple” more, the number one cause of death in an accident isn’t being crushed, it’s the sudden jolt and hitting the car itself. Sturdy cars might survive a collision with little damage to themselves but in doing so, they transfer all that momentum into the passengers. By allowing the car to crumple more easily, it makes the actual stop less sudden and thus less lethal. All that kinetic energy goes into the car rather than you. Think falling onto concrete over falling into water. Yes, at a point, they are both fatal, but that point comes sooner to concrete than water. That’s because concrete has no “give” and stops you all at once while water stops you slowly over time, thus you don’t feel those intense, fatal g-forces.
Note that these cars are also built with cages around the passenger and drivers seat to prevent a car from crumpling you death, so there is a sturdy part of the car protecting you.
Going fast doesn’t kill you in an accident.
It’s the sudden stop.
It’s why you can fall onto an airbag from 50 feet and be fine, but fall onto concrete and you won’t be.
Older cars yes usually were more solid, not crunching or crumpling in the accident. But in an accident when those cars would suddenly stop, your soft fleshy body would still go shooting forward/backwards/sideways depending on the accident, and smash up against that hard, solid car.
We’ve invented airbags that deploy to help prevent this from happening, but we’ve also done what you said, made our cars crumple.
That’s because when our cars crumple, instead of stopping suddenly, the crumpling of the car means you slow down over a longer time, even if that time is only half a second, it can drastically reduce the force on your body during an accident. The crumpling of the car absorbs energy from the accident, meaning there is less energy to do damage to your body.
Cars could be made as a solid block of steel impossible to break, but cars aren’t designed to protect the car, they’re designed to protect your soft squishy body inside.
When you crash you come to a sudden stop and all the energy you had before you stopped has to go somewhere, if the vehicle is all steel and doesn’t crumple or fall apart alot of that force will go into your body.
Now you replace the steel with plastic and when you crash the plastic flies off and any energy it carries can’t come back into your body.
Crumple zones. Because moment is conserved in a collision, the more parts there are that absorb that momentum (either by deforming or flying off), the less the passengers do, keeping them safer. And inside that is a very strong cage around the passenger area that protects them from getting squished.
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