About place your head against eh headrest, some cars have active head restraints that move forward in a rear end collision.
The answer is relax. The more you tense the more likely you are to injure yourself.
This is the perverse reason that alcohol related accidents can see the drunk person the one who escapes with the least injury (comparatively speaking). Drunk people are more relaxed and just sort of flop around more whereas the sober person tense up…stiffens legs and arms and whatnot and get hurt more.
The science is not in on that, and there is quite a bit that refutes it.
In martial arts, there’s the notion of “two hits”. One hit is the person hitting you, the other is you hitting something else. If you’re about to be pushed into a wall, it’s better if you’re already up against the wall. Otherwise, you get hurt by being hit, and get hurt by slamming into the wall
I’m struggling with this one. I’ll give this example:
- I place an eggshell 6 inches from the wall and push it with enough force that is rolls to the wall and cracks a little.
- I place an eggshell against a wall and push it with the same force, it will crush badly.
This is because in (2) the eggshell has to absorb the whole force, but in (1) the force converts to movement.
With a person, against a wall, the have to be rigid - nobody would advise you stay rigid if a person is hitting you.
Another post said in rear end accidents, it is best to leave the brake off, to which I agree, surely this is the opposite of the martial arts “two hits” example.
If you use enough force to crush and egg to push on it, then it will crack more than just a little when you use that same amount of force to accelerate it into the wall.
Here’s an experiment that ensures that the force is the same for both cases.
-
Drop an egg from 6 inches. It will probably crack at least a little.
-
Leave an egg on the table. It will be just fine.
Both are under the same amount of force, it’s just in the first case, you have exactly the “two hit” issue of which you seem to be dismissive. It has those six inches to be accelerated by that force.
They are not under the same force, the dropped egg underwent a pretty high acceleration ie experienced a force when it stopped and the kinetic energy needed to be absorbed which it was in the breaking if the shell.
I’m not sure whether you are agreeing or disagreeing here.
They are both being accelerated towards the table by exactly the same force, 1G.
In the case of the egg sitting there, it is not undergoing an additional force as it suddenly matches the velocity of the table.
This is exactly analogous to being in a rear end car accident, except replace the egg with your head, and the table with your headrest.
ETA: I guess there are slight differences: The headrest is softer than a table, but you are also going to be experiencing more than 1G of acceleration.
If you use enough force to crush and egg to push on it, then it will crack more than just a little when you use that same amount of force to accelerate it into the wall.
Here’s an experiment that ensures that the force is the same for both cases.
- Drop an egg from 6 inches. It will probably crack at least a little.
- Leave an egg on the table. It will be just fine.
Both are under the same amount of force, it’s just in the first case, you have exactly the “two hit” issue of which you seem to be dismissive. It has those six inches to be accelerated by that force.
Have I missed something here? These are not comparable:
- Leave an egg on a table = zero force
- Drop an egg from a height and that’s a lot of force.
If you use enough force to crush and egg to push on it, then it will crack more than just a little when you use that same amount of force to accelerate it into the wall.
How could this happen? If I push an eggshell and roll it, the force from my finger is transerferred to the motion of the egg, meaning less is used to crack the shell.
I’m not sure what you may have missed, but you are correct that they are two different situations, which is the point that I am getting at.
This is not correct, it is experiencing 1G of force.
When you drop an egg, it is experiencing that same exact 1G force, however, it now has space to be accelerated by that force.
Well, now you are specifically saying that you are putting less energy into the egg as you push it than you were putting into it by crushing it into the wall.
Are you saying that you just tap the egg for an instant, and stop pushing it before it reaches the wall? If so, this is not analogous to being rear ended, where the force will be sustained for the entire time that your head is being accelerated towards the headrest. In order to be analogous, you would have to keep pushing the egg with the same force all the way to the wall.
Try an experiment with the wall.
Get a spring, put the egg between the egg and the wall, and increase the force on the spring until it just cracks the egg.
Now, get another egg, and pull the spring back 6 inches. When you release it, the egg will splatter with far more violence.
Too late to edit:
I meant spring, there.
Anecdote:
I was rear-ended, and came out of it unscathed, except that the car was totaled… and I had whiplash. Not too bad, but really sore for a week.
So the next time when I saw it coming, I pressed my head back against the headrest, and ended up with another totaled car, but no whiplash.
Suppose my stationary vehicle is a motorcycle. My best option is get out of the way and let the rear ender hit the guy that was in front of me, but what is my second best? Hold the bars tight, let go and jump, take a 20mph hit from cross traffic or a 30mph hit from behind?
There probably are no good options, jump up and stand on the seat so your legs and body are above the front of the on coming car? Probably impossible to do though but if going left or right is not an option, up is all you have left. Staying still is the worst outcome I would think, obviously depends a bit on the speed of the expected impact, but at 30mph I’d suspect diving out to the side has a better chance , rather than certainty of being seriously injured or dead staying still.
What is the effect of having junk in the trunk during a rear end collision? Do people tend to be injured by stuff? If I have a load of feather pillows in the trunk, I would think that the crumple zone built into the car would not be impeded, but if I were carrying a load of bricks, how much worse off might I be?
A few years ago the father of a 'Doper was killed at a traffic light when his motorcycle was smashed into the back of the stopped pickup truck ahead when the bike was rear-ended by a drunk who braked waay too late.
There are no good options. Even assuming you knew it was coming; the rear view mirrors on bikes are rather more limited than on cars.
Lots of variables to discuss there. Bricks make your vehicle heavier, which reduces the amount it’s accelerated. But bricks impede the crumple zone. And they are individual fragmentary missiles. Net, net, probably more harmful than helpful.
Story time:
Back in the 80s I was at a mini golf course backed up to a freeway. (Aren’t they all? Why?). Traffic was steady but light. We all heard squealing tires & looked over to see a car going fast (90ish?) spinning madly out of control. He spun into the median, bounced off the barrier and then across all the lanes finally stopping in the outside shoulder not far from us. This was pre-cellphones.
A bunch of young spry guys including me, quickly vaulted the chain link fence and ran the couple hundred yards to this guy’s badly mangled car. The entire ass end of the car was both smashed and smeared with bright red liquid. Kind of a gut-wrenching sight as we’re dashing up all out of breath…
The guy, drunk out of his gourd, clambers out of the driver’s seat apparently none the worse for wear. Though we prevailed on him to sit still until the paramedics eventually showed up.
The red stuff? He’d had a few cases of red spray paint in the trunk and in one or another impact they’d gotten crushed and burst, spewing solid paint and drippy splatters everywhere. Looked like the aftermath of the bathroom shower execution scene in Godfather.
Whew!
I just saw this thread, and about half of what I wanted to say has been said, and said well.
Here is the other half:
Force on an egg on the counter: mass*acceleration due to gravity, mg down, equal and opposite force up from the counter holding it in place. Net acceleration is zero.
Force on an egg falling: mg. No opposite force from the counter, so there is a net acceleration.
The important part is - Force on an egg when it hits the counter after being dropped. That egg is decelerating quickly. If it is decelerating at 5 gs (say 0.5 m/sec to zero in .01 seconds) then it will see 5x the force of just sitting on the counter. That force is the counter pushing up to decelerate the egg.
As far as the car collision:
-Look straight ahead
-Keep your arms on the steering wheel, at or below the equator (9 and 3 o’clock)
-Put your head against the headrest
-Relax (being drunk doesn’t help, but relaxing will)
-Braking
-if there are no hazards ahead, break really hard. The force of the tires on the ground will reduce your acceleration, which is good. Another way to look at it is it will absorb energy that otherwise might go into you.
-if there are hazards ahead, breaking may cause you to spin and lose control. Wait until after impact, then brake safely.
-If you think of it, put the car into neutral because if the car is not totaled, damage to the transmission will be less likely
Two hits:
My intuition is that being against a wall makes the first hit a little harder and the second hit a lot softer.
I need to think about that for a bit.
I still can’t picture what you mean. Putting your arms behind you in the event of a rear-end collision seems like the perfect way to break both your arms.
The mirrors are smaller than what’s in cars, but if aimed correctly, they still tell you what you need to know.
We riders are soft and vulnerable, but we’re small, so we can go places cars can’t go. Standard advice for bikers at a traffic light/jam is to come to a stop near the edge of your lane, keep it in first gear, and watch your mirrors, being ready to scoot out of the way, around the car in front of you, if a car approaching from the rear doesn’t seem to be stopping. I also have a habit of flashing my brake lights a few times as a car approaches from the rear (squeeze/release brake lever a few times).
How about water?
Fill your trunk with a whole bunch of 5 gallon buckets of water, seems that should do quite a bit of energy dissipation.
Gotta be quick to get them in there before the car hits though.
Gravel could work too, I think.