Suppose a car going about 100 km/h hits a 20-meter-thick block of mattress foam. What happens to the car?
Is the block of mattress foam secured to the ground? If not, how high and wide is it?
Let’s say it’s 5 meters tall, 5 meters wide, and braced against the bottom of a cliff face.
the front end of the car gets smashed in. and the “mattress foam” gets torn up quite a bit.
Would the driver of the car survive?
probably, if it was a modern car. and if the impact was full-frontal; the compression of the foam and the probable partial collapse of the car’s crumple zone would likely reduce the shock impulse felt by the occupants.
Some runway arrestor beds use a cellular concrete foam. They’re designed to stop a fully-loaded 747.
Couldn’t the foam display elastic spring back and throw the car backward from whence it came , well perhaps upside down or something ? at approx 50% the original speed that would seem to mean it would be out of control at speed…
The exact property of the foam would matter. Mattress foam, rubber or as strong as, constructed for long life, may act as a trampoline and throw the projectile back.
Polystyrene foam, easily torn and squashed permanently can just absorb the hit and leave it sitting still.
There’s grades in between , then there could be a foam block made of various grades…
Well let’s do some basic mechanics.
The real issue here is acceleration (well, deceleration). There are a few possibilities. The foam might be too soft such that the car is still moving at speed when it has fully compressed the foam, such that it effectively hits the cliff. Another possibility is that the foam is too hard such that it decelerates the car fully before the car has travelled fully into it. Another possibility (and frankly probably the most realistic) is that the foam is going to get harder and harder to compress as it gets compressed so that deceleration is not linear. I’m going to assume this foam is neither too hard nor too soft, to give our car the best chance. I’m going to assume it decelerates the car linearly because otherwise the math is too hard ;).
I’m also going to assume that the foam is compressible to 95% of its original thickness ie it can squash down to 1m thick.
That means the car has 19m to go from 100km/h (27.8m/sec) to 0km/hr.
It will traverse that 19m at an average speed (assuming linear deceleration) of 13.9m/sec (half of 27.8) meaning it will take 1.37 seconds to fully compress the foam.
Acceleration is 2d/t[sup]2[/sup] which is 2 x 19/1.37[sup]2[/sup] which is 20.3m/sec/sec which is 2.1G.
I don’t know what that would do to a car exactly - it might stove in the front bumper a little - but it isn’t going to bother people inside one bit.
The OP brings back a scary memory.
I was on a lonely stretch of Interstate late one night, somewhat lulled by the boredom, no traffic in sight.
Suddenly an enormous object looms up ahead, blocking my lane and part of the passing lane. There’s no time to avoid it. I barely have time to start braking, and
WHAM!!!
I have hit (and knocked aside) what appears to be a giant styrofoam block. No damage, but I was wide awake for quite awhile after that.
Now, if there’d been a truck (or cliff) hidden behind the styrofoam block, the outcome probably would’ve been less happy.
Do you have any idea where the Giant Styrofoam Block[sup]TM[/sup] came from? That seems like an odd thing to appear in the middle of the road.
How big was the Giant Styrofoam Block?
It was the pillow of the Big Giant Head.
1G applied to the front contact area of the car is equivalent to standing a car on its nose, with the full weight of car borne by the front bumper/grille. The tires, wheels and brakes can decelerate a car on the road at something close to 1G, but those components are designed to take that kind of load; the front bumper/grille are not. This seems virtually guaranteed to do significant damage to the front end.
Now with that car stood on its nose, set another car on its rear bumper so that you’ve doubled the weight on the first car’s nose. You’re gonna cave that front end in pretty good.
1G of decal will have the car’s occupants leaning into their seatbelts pretty good. 2.1G, much more so. Imagine hanging in your seatbelt in the vertical car described above, and then imagine your identical twin (except with 10% more weight) spooning you from behind. The seatbelt won’t injure you, but I wouldn’t say it isn’t going to bother you either; you’ll get the wind knocked out of you pretty good.
True.
But that’s rather a different process. The weight of the aircraft crushes the foam, and then the effort of plowing the landing gear through the deepening foam is what provides the braking force.
The best analogy in a car would be driving off a road into steadily deepening powdery snow.
It was taller than the hood of my car and seemed about as wide, though I didn’t have a lot of time to take mental measurements.
I have no idea where the thing came from. It might have fallen off the back of a truck, hatched from a styrofoam egg or been dropped by aliens.
Good link. Thanks.
I agree it’s the same idea, except for many truck ramps there’s also a lot of uphill. So the decel is a mixture of surface drag and simply coasting uphill.
I didn’t mention truck ramps not wanting to get that uphill part mixed into it.
Don’t know if this has been addressed,
But a lot of racetracks (European mostly) have foam along the wall in the most dangerous parts of the track.
The collision is amazing, the car is destroyed, foam flys everywhere, and the driver walks away.
Well you’re right. I suppose I was thinking relative to what normally happens to passengers when a car hits something at freeway speed.
The kind of foam will make a big difference here. Old fashioned mattress foam was available in different densities, but none of it was strong stuff. That stuff might disintegrate as the car plows into it, effectively acting like a loose snow bank. Modern memory foam and silicon foams are much stronger material, and denser with many more smaller voids. That stuff will slow the rate of de-acceleration when the car first hits it but pretty soon it’s going to act like it’s close to solid as the air in the voids gets compressed without destroying the foam material.
ETA: hmm, this got me interested in posting a new question