A couple of comments on the "Center punch and blade to cut seatbelt?" thread made me think of this.

I was at a brain trauma unit for a while.

While there I was surprised by how many people had been hurt by stuff flying around their vehicles in an accident instead of bumping their heads on windshields or door posts.

Things as seemingly trivial as a clipboard in the back seat.

Everything that is loose in a vehicle becomes a flying missile aimed at you if you are in an accident.

If it is on the dash board, rear window deck or sun-visor it is likely aimed straight at your head.

If you are in an accident at 30 mph that is how fast it will be moving.
You you are driving at 60 mph when the accident happens the missile will be going 60 mph.
At 60 it will have 4 times the momentum it did at thirty and will do 4x the damage instead of 2x.
(force = mass X velocity^2)
Some professional pitchers can throw a fastball a bit faster than 90 mph.

Even a cheap pulp fiction novel will do serious damage to your brain if it hits you at any of those speeds
So think about if it was a water bottle or a wrench.

It would be far safer if loose stuff was in the trunk.
Next best would be in a compartment.
On the floor is a distant third.

So, how many of you have missiles aimed at your head inside of your car when you are driving?

All my stuff is on the floor, usually on the back-seat floor.

One thing that has always annoyed me are the people who refuse to wear a seatbelt, yet have a baby or child in a carseat or seatbelt. In an accident or rollover, the DRIVER is the moving object.

Sue

"At 60 it will have 4 times the momentum it did at thirty and will do 4x the damage instead of 2x.
(force = mass X velocity^2)"

Formulas and definitions not quite right, but point well taken.

Force = mass x acceleration(not the same as velocity squared)

Momentum = mass x velocity

Energy = 1/2mass x velocity squared

At 60, it will only have double the momentum.

Damage is a bit relative. Ballisticians have argued for decades about what is an appropriate calculation for approximating damage from a projectile. I prefer the force calculation, mainly because it is the only formula that deals specifically with terminal ballistics, although it too is an incomplete calculation.


The bottom line is getting hit in the head with a clipboard at 30 mph is not generally as devastating as one at 60 mph, and both situations should, and can be, avoided taking the recommended precautions.

You are right. I should have said Kinetic Energy.
Momentum is conserved.

(1/2)mass times the velocity squared is equal to the force times the distance it takes to stop the flying objects in your vehicle.
(force X distance) = (mass X velocity^2)/2

This gives you the force as Footpounds and the squaring of the effect due to doubling the speed holds true.
If you get in an accident at twice the speed that bobble head dog in your rear window will go 4 inches into your skull instead of just 2 inches.
Traveling three times as fast it takes 9 inches to stop as it passes through your skull.

I just am really bad at remembering formulas that I seldom use.

However, I have made checking for loose objects a standard procedure whenever I get into any vehicle now.
Right up there with all the other standard checks.

If I am involved in a collision and the stuff on my truck's rear seat is propelled forward, I am screwed. I carry so much gear that it would take a miracle not to be hit by multiple objects. I should install a cage like we have in our police vehicles or, at least, strap the stuff in with the seat belts. Hmmm, I wonder if anyone makes a cargo net that snaps into the seat belt receptacles.

Excellent post. Thanks for the reminder.

Mythbusters did a good segment on this!

I have not seen it yet but I looked up the episode from their site with the description.
If I can find it I will definitely watch it.



My guess is that a Kleenex box wouldn't be heavy enough to do much.
Then again I might be wrong.

What does a box of Kleenex weigh and how hard does it hit at 30 mph and at 60 mph?
and in real life there is friction and air resistance.
Balloons will actually not move much in a crash as they are about as dense as the air is.

So what was their answer Mike?
You have me really curious now!

I can't recall if the Kleenex could do any major damage. I think the most it could do is give you a nasty papercut. The issue was that the headrest of your seat should deflect that.

Something more tangible, however, would definitely have your number on it.

Been awhile since I saw that episode.

scafool, your homework assignment is to watch the episode and report back. LOL!!!

I am pretty obsessive about this too. I keep my gear in the trunk, with smaller items in the center console. I have been in an accident and had the radio come out of the dashboard; I'm just glad the wire harness held. My wife is pretty bad about loose stuff, but she hauls so much kid equipment that I can't talk her out of it. There's really no place in a minivan to secure the stuff; I could strap it all down but it would be so much of a hassle to her that she'd leave it all undone.

Another thing to consider is securing pets in the car; not only can they get underfoot when you're trying to brake, but they can bounce around a lot too. We hadn't even thought about it until our training instructor told us about an accident she was in. She couldn't get her dog in the car for almost a year because he was so afraid it would happen again. $20 for a simple harness that will clip to the seatbelt can save a lot of problems...