this post was submitted on 05 Apr 2026
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I am not sure why the difference in energy related to vehicle mass is relevant here as humans have an insignificant amount of mass compared to either vehicle, so transferred energy should be roughly the same. However, the difference in how the collision plays out (pulled under Vs thrown above) should be a huge impact
I see what you did there.
The higher mass and force transmitted by a truck means the human will be thrown further and possible impact other objects at a higher speed
Not all of that energy is transferred. The car doesn't stop as if it hit a wall. Usually it barely slows down. The human on the other hand gains at most the kinetic energy corresponding to their body mass and the speed of a human bouncing forward off the car at around the same speed as the car was going, so a tiny fraction. Of course impact geometry will determine the specifics and pickups suck there too. The important thing about kinetic energy is that it's dependant on the square of the velocity. That's why speed kills. The mass is just a linear relation.
The issue is energy transfer doesn't care about weight of the human, more kinetic energy will impart more speed to the human during the impact impulse. Imagine a solid bowling ball hitting a beach ball vs a plastic hollow bowling ball hitting a beach ball
You are thinking of perfectly elastic collisions. That's a fantasy and not applicable to the real world. A human body isn't a beach ball and cars have crumple zones (although I believe pickups suck in this regard as well).
And your comparison isn't applicable in terms of masses either. Both a sedan and a pickup are way heavier than a person.
Edit: Without getting too deep into the math, let me put it this way: The energy of the impact is equal to the energy that the car loses during that impact. The car doesn't lose mass, so it depends instead on how much the car loses velocity. That depends on how the mass of the other object stacks up against the mass of the vehicle. Car hits something much heavier than itself? It stops and all of it's kinetic energy is expended. Car hits something much lighter? A bug on a windshield. A human obviously isn't quite as neglibly light as a bug and the mass of both the human and the vehicle do factor into this, but with both a sedan and a pickup truck, the speeding vehicle never expends more than a fraction of it's kinetic energy on the impact itself. The rest of it is dealt with via breaking, and a pickup will have a harder time slowing down due to it's kinetic energy.
Car crumple zones are tuned to prevent damage to the car, not to pedestrians. If they were they would have airbags on the front of the car. A car can kill a pedestrian by hitting them with a crumple zone, without that zone crumpling.
This means most of the non-elasticity is in the pedestrian's body; how they flop onto the hood of a normal car, and how their bones crumple and flesh splatters before their brain and vital organs do.
Of course if a car hits a pedestrian hard enough, the crumple zone will crumple to reduce damage to the car, but that's overkill as far as the pedestrian's life is concerned.
That said, if you (unrealistically) assume the speed at impact and the geometry of the hood are the same, the difference between a car that weighs 20 times what a person does and one that weighs 40 times that is (40/41 - 20/21), or only about 2.5%.
Realistically, the weight increases the braking distance and the hood geometry makes the pedestrian's body perish more elastically.
Well, yeah. I can kick a dent into a car, but mostly I just raised crumple zones to emphasize that these are inelastic collisions we're talking about.
And yes, the breaking distance is pretty much the only way that vehicle mass is relevant for pedestrian survival.
Partially correct, the speed (technically acceleration) of the human after a collision is limited by the decceleration of the moving object caused by thr human. Since a car and a truck decellerate about the same amount when receiving the counter-acceleration of the human, the force transfer remains similar.
The bowling ball will not slow down in the slightest when is hits the beach ball, accelerating the beach ball up to it's speed.
The plastic ball will lose significant speed hitting the beach ball, decelerating itself significantly as it accelerates the beach ball.
I'm going to pick some easy math speeds/masses for demonstration. 2,000 kg sedan, 4,000 kg pickup and 100 kg human. Starting velocities of 20m/s and 0m/s. An impact/acceleration time of 1s.
The sedan hits a pedestrian with (f=ma) of 40kN. It takes 2kN to bring the human up to 20 m/s. So the sedan will be somewhere around 38kN, or 19m/s at the end of it and the human absorbing 1.8-2kN.
The truck has f=80kN. Same 2kN for the human. So the truck will be somewhere around 78kN or 19.5m/s at the end. With the human absorbing 1.9-2kN
In either case the we talking a difference of 1.8-2kN for the human. Regardless the mass (and total force) of the vehicle, the relatively small human as a maximum force they can absorb. And that maximum force is heavily related to the speed of the larger object.
Not to say trucks/SUVs aren't deadly for other reasons (like where and how the force os transferred)