So this article claims the small cars have significant disadvantage in crashes with big cars.

However, they don't say anything about the advantage of smaller weight in terms of stopping distance, maneuverability, being able to change direction rather than absorbing the crushing forces, that could do more damage to a heavier vehicle that is harder to move.

Imagine what fares better to a hit with a spoon from the side - a heavy egg or a light ping pong ball...

https://www.technologyreview.com/s/4...-big-cars-win/

Thoughts, comments?

 

Not a physics expert, but I'd rather be in the larger modern vehicle.

If you read the article, it's the transfer of forces that affects the smaller car more. The bigger heavier car transfers the force to the smaller and and slows down slower. The smaller car stops, then bounces off so you have double the forces affecting it. The adage "It's not the fall that kills you, it's the sudden stop" comes to mind.

Here is the video that your link has a broken link to: Crash tests show how vehicle size, weight affect safety

Your example of the egg and the ping pong is flawed IMO. The egg will absorb it better because the shell will crush and absorb some impact (like what a car does in a crash with crumple zones), while the ping pong will just bounce off to who knows where.

 

What conclusion from my example did YOU draw that is flawed?

Let me ask you, if you had a choice of being in a crash against 4000 lbs accord in a 2012 Honda fit, would you prefer the fit to be empty with one driver or be carrying five 200 lbs passengers plus 300 lbs cargo?

Please explain your answer.

 

In your scenario, it wouldn't make a difference if the vehicle is empty or packed to the gills. The accord has a larger frontal area and crumple zones, so it would transfer the forces slower than the Fit.

 

I would disagree.
A moving object's kinetic energy is the result of velocity multiplied by mass. Therefore, a heavier Fit will have to deal with A LOT more energy, and therefore the damage that energy does to its own structure. Again, imagine a brick wrapped in foil paper rolling on a skateboard being crashed into an object, vs that same foil being wrapped around a sponge. The heavier brick will do more damage due to possessing more energy.

Remember, the second law of thermodynamics states that the energy is neither created nor lost, it just changes form. So, more gas had to be burnt to accelerate the havier fit up to speed, therefore this energy will be converted into more damaging force that will be dissipated in a collision (likely in severe, unpredictable and potentially damaging way to Fit's occupants as well as the passenger in the Accord's). The lighter Fit, would not have this much energy to dissipate, though.

 

My argument was only that the article failed to note that lighter vehicle have the advantages over heavier vehicles in some types of collisions.

The relationship between vehicle mass, its rigidity, its ability to absorb energy via structural deformation, its maneuverability are way too complex to say that lighter cars are by definition more dangerous than heavier cars in ALL scenarios. Here is an example

 

I have to laugh at your example of wrapping two items of completely different composition in foil to explain your thesis.

Also the video is comparing a modern car with an older design. Compare two modern cars of different sizes/weight and it'll show a different outcome. Even in the last 10 years there have been a lot of advancement in safety engineering.

 

On one level I don't care.
I''m driving a sub-compact vehicle. With airbags, uni-body construction, and crumple zones.
But it seems near to undeniable common sense to believe if I drive head on into a much bigger vehicle, I'm likely to suffer much more consequence than the person sitting in the much bigger vehicle. You cannot remove the realities of physics and momentum.
It's not spoon vs heavy egg or ping pong ball....It's larger vs. smaller, and less mass vs. more mass.
And in the vast majority of situations when two objects collide, small vs. large , the smaller mass simply will not fair as well as the larger mass.

But really, this is just a reality of the world we live in. With airbags, crumple zones, and the design put into the modern automobile, I'm perfectly happy with the degree of safety offered.

Accidents in the real world are unpredictable. Am I hitting something stationary? Am I hitting a vehicle of similar size and weight? Am I hitting or am I being hit by a much larger vehicle?
There is no way to really predict.
Today's modern small vehicles are much safer than similar sized vehicles just decades previous.
But physics still apply.
I'm not willing to bank on the prediction of what would be pretty rare situation, where I "might" be hit by something bigger and heavier and simply skid or slide away.
We are talking about the forces of not only size and weight, but also momentum from two propelled objects hitting each other and usually in those situations...bigger and heavier, will impact smaller and lighter to a much greater degree.

 

Exactly, and now just use some imagination to imagine numerous scenarios in collisions when lighter vehicle weight is of benefit. That's what the article fails to mention.

Heavy car being dropped onto its room, heavy car hitting a pole and slicing itself in a half due to all the momentum of its heavy body... the scenarios are numerous.

The article fails to mention that, and that is why I shared it. No need to state the obvious about head on collision of two objects of different masses.

 

 

They, automakers and the institutes that test for crash safety, test for the most common predictable factors, which will in the vast majority of situations be momentum and mass.
Therefore while it's arguably possible to create specific scenario's where one could imagine lighter and smaller being "safer", I think the exercise entirely unnecessary, and in majority invalid.
I think YOU DO have to discuss the collision of two objects of different masses, because in the majority of accident situations that is what you are dealing with, NOT...strange blue moon scenarios, where large cars are "sliced in 1/2" or smaller cars "skid to safety".
Sorry, I agree with the overall reality and premise of the original article.
In the majority of situations not tainted by flights of imagination and fancy, in an accident larger and more mass coming into contact with smaller with less mass, the potential safety advantage goes to the larger object.

 

I was rear ended at a stop light a few years ago, my more "maneuverable" tacoma made no difference to the box truck. Luckily it was a low speed collision and wasn't seriously hurt.

 

At my age I'm not worried. I'm far more vulnerable on my Harley than in the Fit, and I'm not giving up the Harley, either.

Simple solution: don't crash!

 

My '07 Fit Sport was T-boned by a '90's Cadillac Sedan de Ville @ speed; side/seat airbags deployed, and I walked away without a scratch. Front wheel had a 3" inch hole in the middle of the rim, the tire itself had a 2" inch hole in the side wall, the CV joint was pulled from the transmission, and the control arm broken. My insurance totaled it, but amazingly, it turned up on Craigslist repaired and with a salvage title! So, all in all, I considered it a good outcome!

 

I read that you have two different premises here.

Premise 1. A more maneuverable is better able to avoid a crash.

Premise 2. A light car is better at not succumbing to damage due to energy transfer because it has... less momentum? less mass? less stored energy to transfer?

Thoughts on 1: Sure. This is generally true. Much like a sportbike can avoid crashes better than a Harley. Best way to avoid damage is to not be there. Makes sense.

However, so much of that is dependent on the driver's reflexes and driving ability that it's nigh unmeasurable. It's mainly up to the driver to get out of the way. Their vehicle's characteristics can simply make it a bit easier or harder to do so. This is why this aspect is missing from studies. You can't reasonably test for driver ability. It's too variable and quite subjective. All you can test for is what happens in the event a crash happens.

Thoughts on 2: Independednt of design (since your premise does not really take into account crumple zones and other structural energy-mitigation design), I guess you can make the argument that in those rare cases of being wrapped around a tree the reduced mass of a lighter vehicle means it may be less likely to be torn in half. As you said, less energy to dissipate. There is some truth to this, but I don't think it's as relevant or important as you think it is.

If you imagine your ping-pong ball with people inside, those people are going to be broken horribly if the ball does not absorb impact. The crushing of the eggshell is what saves people from terrible whiplash-type shear forces.

fitchet's last post (#11) is exactly right. Automakers test for common and objectively measurable situations. And, as a general rule, especially if you ignore crumple zones and other design characteristics, the winner will be the object with more mass.

 

The problem with applying generalities about accidents to specific instances is that accidents are so "accidental."

 

 

All good points above, and not having much time to respond to each right now (i am going on trip to Arizona in my Fit),

I would like a response to the following question (which I already asked before but didn't see any one respond to).

Would you rather be in an empty Fit in a head on collision with a wall, or the one loaded with 5 adults and 400 lbs of cargo? Let's say the adults are wearing seat belts and cargo is rigid with the body of the car behind the rear seats.

Please explain which scenario is likely to be "safer" for the occupants.

 

u trying to kill your inlaws or something?

 

That question requires one to think in terms of physics...