[echoangle]

Since the heavier vehicle has higher momentum, it would decelerate slower when hitting a semi-static-object, which decreases the forces on your body. The smaller vehicle would stop much quicker and you would jerk forward. So a heavier vehicle at the same speed would probably be better, all else being equal. And that's neglecting the additional material a larger vehicle typically has that deforms over longer distance than with a shorter car.

[resource_waste]

>it would decelerate slower when hitting a semi-static-object

You just changed the problem.

[echoangle]

Did I? Trees and electrical poles aren’t completely rigid, right?

[mrguyorama]

To a car? Many trees are! They are quite rigidly affixed to the ground.

[echoangle]

So many are and some aren't. So in many cases it doesn't matter which car you're in, and in some cases the heavy car is better. That means the heavy car is still net better.

I still haven't seen a single argument why a smaller car would be better in a collision.

[resource_waste]

Yeah, the point was deliberately to show that a small car performs better in such situations.

If you had to change the problem, it shows you were avoiding the uncomfortable truth.

[echoangle]

But a small car doesn’t perform better, why would it? Surely a large car is better when driving into an electrical pole than a small car. What advantage does the small car have?

Also, just to clarify, how did I change the problem? The problem with car crashes is rapid deceleration which injures you, and lighter cars are worse in that aspect compared to heavier cars.

[resource_waste]

Less momentum

[echoangle]

And can you explain why less momentum is better for the passengers? The thing that injures you in an accident is acceleration (or more accurately deceleration), so you actually want more momentum.

Imagine sitting in a large truck vs a kei car and driving into a brick wall. One has the chance to deform the wall which decreases the speed comparatively slowly. The other one abruptly stops when hitting the wall.

Unless the collision target doesn't deform at all, the higher momentum is better. And if the target is completely solid, a larger typically has a larger crumple zone which is better, too.

I cant come up with any reason to prefer the smaller car/momentum, except in very constructed scenarios (driving over a cliff with a weak fence for example).

[K0balt]

I’m not a crash test dummy, but….

If the object is completely fixed and effectively inelastic, the main determinant in survival is the distance over which the deceleration of the occupant occurs, assuming a lack of cabin intrusion.

So the mass of the vehicle is ideally fixed in relation to its rigidity, and it’s not better to have less, or more, mass except as the ideal ratio to the rigidity of the vehicle.

What you want is a vehicle that decelerates as slowly as possible over the greatest possible time/distance.

A light vehicle that is very rigid is equally terrible as a heavy vehicle that is very rigid. What matters is how many millimeters it takes for each vehicle to come to a complete stop after colliding with the immovable object.

There are a lot of combinations of vehicle mass and rigidity that meet the ideal here, and it is not sensible to assert that a massive or a lightweight vehicle will be ideal in this case.

What you want is a vehicle that, at the speed of the collision, deforms the most completely and to the longest distance possible without incursions into the passenger compartment.

Ideally, the vehicle would have a very long and well engineered crumple zone in front of the occupants. Here, assuming similar material engineering of the impact absorbing structure, length is king. All things being equal, a car with a stubby front profile will expose its occupants to twice the acceleration as one with a 2x longer hood.

Still, the vehicle must have enough mass that the crumple zone is fully compressed at the speed of the collision. If it’s too light, it will decelerate before the impact absorbing distance if fully used.

If it’s to heavy, it will still be moving when the crumple zone is fully exhausted, and either a sudden peak of acceleration or a cabin intrusion will occur when the passenger cage becomes involved in the deformation zone.

I’m going to guess that on average, you’re still better off in a full sized SUV than In a more sensibly sized vehicle, hitting an unmovable object at speed.

You say you have a background in vehicle safety, so maybe you know something I don’t. Please explain where I’m going wrong here?

[itishappy]

Momentum is resistance to acceleration. Momentum protects the driver.

[itishappy]

Not really, the car itself is a semi-static object, even if you're driving a block of raw steel.

[resource_waste]

I did automotive safety and I can assure you, these act as static for all intensive purposes.

Being a skeptical Socrates doesnt change that the momentum is significantly higher, and you arent moving that pole any significant distance.

I'm not sure why there is such a strong denial of reality here. Is it ego?

[itishappy]

Crumple zones have been a thing for almost a century.

Momentum doesn't matter. It matters in a vehicle on vehicle collision, but since the pole is essentially infinite I'm not sure why you're bringing it up. Acceleration is what impacts the human body, and it's determined by speed and distance. For the same speed, a larger car will have a longer distance to stop, therefore lower acceleration, and less force on the body.

[echoangle]

Even if you assume that the pole doesn't move at all, having less momentum doesn't help you. A smaller car isn't better, in the best case it is equal. But a larger car probably also has a larger crumple zone so it is still better. You still haven't given a single reason why a smaller car would have an advantage.

[floxy]

https://www.dictionary.com/e/for-all-intents-and-purposes-vs...