LameRandomName

This is sort of car related. Technically. Barely.

It's definitely advanced tech though, because I don't think the guys in the other forums could even manage a quadratic equation, let alone

I was watching Mythbusters and they were working on the whole; "Will a tissue box hitting the back of your head at 60mph kill you?" question.

I don't have a fancy test rig, but I do have a pencil, paper and a kitchen scale.

Here's where I'm at:

863.76 Kilogram-Meters/Second

Now I'm stuck.

I don't know how to convert that into a unit of energy that I can understand in terms of physiological consequences.

Also... Rich...?

This is where you come in.

As a medical professional, I figure you would be in a position to judge the potenial carnage.

OldSStroker

I'm a little confused with your 863.76 Kilogram-Meters/Second figure. A box of 160 Kleenex tissues has a mass of 268 gm +/- a couple. 60 mph is about 26.82 m/sec. Linear momentum is m * v or mass times velocity. I get (.268 Kg* 26.82 M/sec) = 7.188 Kg-M/sec. You got 120 times as much. Hmmmm... Even if you used a larger box of tissues of 322 gm., you would still be 10^2 or 100 times the momentum. Either I don't understand the concept or one of us is a couple orders of magnitude off.

To assess the damage caused by a collision we look at the force caused by the change of momentum of the tissue box. IOW, assume it decelerates from 60 mph to 0 when it strikes the noggin. This can be called the impulse-momentum theory and is equivalent to Newton's Second Law.

Before we get into numbers, we need to know about how long it takes to decelerate the tissue box. If it were basically uncrushable (a brick), it would decelerate in the distance it penetrated the skull, let's say 25.4 mm (1 inch). If the box crushed completely, it would be about 254 mm or ten times as much. The analogy is hitting an imovable object with an M1 Abrams tank that doesn't crush much, and hitting it with you car which crushes a number of feet assuming a 60 mph impact. Much more force is transferred to the occupant (or the bridge abutment aka your head in your example) in the short time it takes the object to travel one inch than if it takes 10 inches to stop it. Personally I think they chose a tissue box just because it will crush in a 60 mph impact.

We can use the impulse approximation if we assume that the force of the flying snotrag box acts on the head for a short time but is much larger that any other force present. That's probably an ok assumption. It's travelling at 26.82 * 1000 = 26820 mm/second. With a constant deceleration in 254 mm (length of box), it might take about 19 milleseconds to stop. (26820+ 0)/2 = 13410 mm/sec avg. velocity / 254 mm = 52.79 1/sec or .0189 seconds.

Using Issac's 2nd Law, change in Momentum(delta p) = F/change in time (delta t), we get F= delta p/delta t or 7.188/.0189 = 380.3 Kg-M/sec^2.

Again using F=Ma, solving for acceleratuion we get a = F/M. If the average noggin has a mass of about 6.8 Kg, we get a = 380.3 Kg-M/sec^2/6.8 Kg or 55.92 M/sec^2. Dividing by 9/8 M/sec^2 (1 g) we get about 5.7 g's. applied for 19 ms. Now unless my numbers are way off (by a factor of 10-20), that g load for that time isn't anywhere near lethal. Here's where Rich needs to make a call.

FWIW, 100-120 times that figure or 570-684 g's has a P sub k (Probability of Kill) well over 1.0. IOW, you be dead many times over.

Someone needs to check my math (and also physics), but my conclusion is NO, the 60 mph impact from a standard Kleenex box probably won't do you in, but it will sting a lot.

My $.02.

MachinistOne

Basically a box of tissue does not weigh as much a a baseball, and a baseball will concentrate it's mass behind a smaller point of impact causing more damage because the load is not spread out as much on your dome. If pitchers can hit guys in the forehead or somewhere where the helmet doesnt cover at more that 80mph without death, then I doubt a kleenex box will cause you to hemmorage and die.

A good place to look for this kind of information is helmet manufacturers, to be snell and DOT approved, they have to test all sorts of impacts and their effects...their was a real intresting article in last months hot bikes that talked about the rating given to head impacts and how much actual force it takes to cause a life threatening injury.

LameRandomName

My box of tissue was 366grams.


You know, this question seemed a whole lot less silly last night...

OldSStroker

Yeah, didn't it. I still think your momenmtum is way off.

It's been many many years since I worked with head impact studies, but if I recall the damage depends on a combination of gs and time. The head can withstand lots of gs for a millesecond (.001 sec), but as the duration increases, the max g drops off rapidly. I'm sure that data is available on-line, but we've probably wasted enough bandwidth on this already.

Now I know why I don't watch those shows.

Zero_to_69

Wait, I want to waste more bandwidth on this one!

I'm trying to picture a scenario where a tissue box would be moving at 60 MPH
to begin with (waiting for the, "in your car response").

Aside from that, even if the box was traveling at 60 MPH, I would imagine the
rate of deceleration after removing "the power source" is going to be huge.

There just isn't enough mass to cut through the air (consdering surface area
of any side of the box)...or even keep the box directional for a decent distance.

So...by adding some spoilers/air foils, a 'fast back' style box end, and cone shape front end, we could really make this tissue a killer.

OldSStroker

Zero, imagine it falling from a 4th or 5th story dorm window. Ma Nature supplies the constant power source. One could run an interesting experiment to measure vertical velocity and even terminal velocity if the building was high enough. You could even measure the impulse when it hit the ground.

Or Scotty might rig up a tiny impulse engine for it.

Think "out of the box"!



















Pun was intended.

rskrause

I very much doubt a serious head injury from the above scenario. This is assuming a young, healthy person. The part of the head that was struck would play into it though. The occiput (back of the head) and fronmtal area are pretty resistant to blunt force trauma. The side of the head, quite a bit less so due to a number of anatomic factors.

There are a couple of different kinds of brain injury. First, you can gross disruption of brain tissue from direct apllication of force - typically penetrating trauma or massive blunt trauma with gross disruption of the skull. The latter is pretty rare - I saw it once wherein it was conclusively demonstrated that a wrecking ball >>>>> a human head. These can cause instant death in most of the latter cases or a more or less severe injury in the case of penetration based on the exact mechanism and location of the injury. There can also be primary brain injury from shearing forces. This is often what happens in car accidents. Basically, the brain is damaged as it twists or recoils inside the skull due to translational forces. The forces needed to cause this kind of damage are quite high, especially when spread over a relativwely large area (e.g the tissue box).

Then there is a large variety of secondary brain injuries and delayed primary injuries. Things like bleeding into the cranial cavity (epidural or subdural hematome, etc.) and so on. The amount of force needed to produce these is quite variable, but from my experience I doubt the tissue box at 60mphh would pack enough punch. Lots of peope get beaned with a baseball at 60mph and while this can cause fatal injury, it usually does not. And a baseball has a lot more mass and delivers force over a much smaller area than a tissue box.

Rich

Zero_to_69

Hey, you're not going to believe this, but I was making a sandwich just now
and saw a box of tissue on the table.

I picked it up and whipped it at the wall as hard as I could (try it, it's fun!).

I was standing about 10 ft. from the wall.

She goes pretty good!

I take back my last statement about directional stability.

LameRandomName

There is also the issue of drag I suppose...

Using Bowling's Aerodynamic HP Calculator (V2.00) and assuming a Coefficient of drag similar to a tractor trailer with the following inputs:


Coefficient of drag = 1.2
Frontal Area = 0.33 sq feet
Test Temperature = 70.00 degrees F
Test Barometer = 30.00 inches Hg
Vehiche MPH = 60


That gives us the following results:


Air Density Computed is 0.00233
Aerodynamic "Drag Factor" is 0.00099
Rolling "Drag Factor" is 14.22689
Computed Aerodynamic Horsepower Required is 1
Computed Rolling Horsepower Required is 0
Computed Frontal Lift Force is 0 Lbs.


Of course, I don't have the slightest idea what all that means, but it sure looks groovy.

OldSStroker

Rich,

Very interesting info, well maybe with the exception of the wrecking ball/head impact thing. In the days before airbags, a lot of automobile testing was done on head impact on instrument panels, top of steering wheel and anything a belted or unbelted body would hit in a frontal vehicle impact. Here the head, which has the approximate mass of a bowling ball if I recall correctly, was the projectile hitting the inside parts of the vehicle.

When the vehicle hits something head on, it stops but the occupants continue on at the initial vehicle velocity. The inside of the vehicle effectively backs into the passenger. This is where restraints and airbags help. It's this "secondary collision" that does the damage.

The forces are much larger than most people imagine. Passenger vehicle seat belts resist at least 5000 lbs of force before they fail, but some crashes are so violent that seat belts fail in tension. Of course, at that kind of deceleration (load) the crash is probably not survivable anyhow. Racing seat belts are much stronger.

I wish I could have gotten past the "blood & guts thing". Medicine interested me greatly. Never could get past it. My wife is a first assist for a general surgeon. She likes to watch surgery on TV while eating. I can't even watch it with no food in sight. The day's cases are not dinner conversation, needless to say. Trauma seems to me to be the worst case.

So, baseball caps (but not baseballs nor bats) and Kleenex boxes are ok on your rear package shelf, but bricks, bowling *****, and Dominion head castings aren't.

Come to think of it, I've never seen a box of Kleenex used as the fatal weapon in a Law and Order episode.

MachinistOne

I'm an EMT in this county and we don't work patients in extreame car accidents( 60mph into tree ->unresponsive, no pulse) because even though they can look fine from the outside, the secondary collision as you put it will most likely break organs off inside the body especially snaping the aorta it doesn't sound right but that's the SOP.

number77

Oddly enough, I'm currently considering going to med school (i would like to be a trauma surgeon), just because I don't like seeing people like that.

So your just saying you don't resuscitate them?

OldSStroker

My favorite trauma surgeon got his start in VietNam (we're both in our early 60's). He is very laid back. IOW, he never panics in any situation. He is very fast at what he does; less time = more survivors. He doesn't mind getting calls at all hours, especially weekend, holiday or full moon nights, and it's almost always nights.

He doesn't save all of them. If the trauma surgeon is working on them, they are hurt badly. Some are very young, and were perfectly healthy until the trauma. That's the tough part.

If you have these characteristics and can juggle a number of ***** simultaneously (figuratively speaking), trauma might be just the ticket for you.

My analogy of surgery to flying: trauma surgery is more like driving a fighter than a commercial transport. Transport pilots get rich, but bored, with a few exceptions. (Toronto in a T-storm).

My $.02

unstable bob

Funny you should mention the Dominion head casting as being a "no-no" on the rear package shelf. I was able to test that theory w/o having that beret wearing woo-woo or his metrosexual side kick around at all! I hauled one of my heads around for a long time on the package shelf of an 86 Cutless. And one day I was passing Joey's Dog House, and noticed a sign out front that said "Under new management! Special 2 day: 2 for 1 chilli dogs!" Well, I slammed on my brakes so I could bang a quick "u-ey" to get some of those dogs,and 'sho 'nuff...the Dom head flew forward like a cruise {night} missile!
It wailed me in the back of my dome, and then fell to the floor. The only damage was a small chunk broke off the corner of the head. The Dominion head, not my head. So, I guess yer theory is 50/50 Pops! If you are unstable bob gable, it is safe to ride around with a Dominion head on yer package shelf. If you ain't unstable bob, you shouldn't try it at home!