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Old    Baitkiller (baitkiller)      Join Date: Jan 2010       09-01-2010, 4:31 PM Reply   
These are skills I lack. But I have a question. Would it be possible to figure the (force) ones melon takes at impact when face planted on landing toe edge W2W in sea water? I have done this a couple times and well darn it hurts bad, chest, arms and especially my poor head.

The info I can provide is the head in question is 5'-10" at the top edge above the pivot.

The initial travel speed is 23 MPH.

Acceleration is developed from a 70' rope.

If arc is useful than figure maybe 4 feet at the apex.

I have no idea what a head weighs, or how to figure acceleration off the rope length or how to figure force once those numbers are achieved.

I tried last night, dug out the books... put the books away and Goggled. Tore up some paper and my head hurt worse than it did from impact.

I'm just curious because I seem to have a nasty habit of catching that lead edge on landing and things start to happen fast. real fast. Painfully fast.

If you have the school and skills I would be obliged.
Not quite P.U.I. only two beers in.
Old    Ben B (benbuchholz)      Join Date: Oct 2009       09-01-2010, 4:54 PM Reply   
well i can only answer how much the human head weighs.
http://www.youtube.com/watch?v=NqxMlmpB66k

I think there was a thread that covered this already, I'll see if i can find it. someone else might know where it is too and post it. couple years ago when i was in my calculus/physics prime, i could probably figure it out. but no way i could now
Old    Jay T. (wakebrdjay)      Join Date: Apr 2008       09-01-2010, 4:59 PM Reply   
There's an ad for bwearing Lifevests in Wakeboarding Mag now and then that tell you what you are asking.I think it was something like 4000lbs per square inch. I'll try and find it and post their number.
Old    Jay T. (wakebrdjay)      Join Date: Apr 2008       09-01-2010, 5:10 PM Reply   
From ad in WB mag "When you wakeboard your body can travel at 40mph,can hit the water with 3000lbs of force,and without a life jacket can sink in 5seconds."
Old    Jonathan Bay (john211)      Join Date: Aug 2008       09-01-2010, 5:21 PM Reply   
Excluding the much lower claim of 3,000 lbs force for the whole body, let's examine the 4,000 psi claim.

Whew ... 4,000 psi impact force?

My ‘melon’ for a melon measures about 9 inches high and 6 wide.

I’ll guess that the area for an ellipse = about (Pi x height x width).

Does that mean for me the impact of my head alone will be about 340 tons ?!?!?!

(OK ... pointy noses and slope heads will fare better than a pie face.)

Whoa ...

I hope you got a Rhino thick skull.
Old    Jay T. (wakebrdjay)      Join Date: Apr 2008       09-01-2010, 5:33 PM Reply   
Did you see I THINK IT WAS??? That's why I looked up the ad.Wasn't sure the psi was in there ok genus?
Old    Ben B (benbuchholz)      Join Date: Oct 2009       09-01-2010, 5:36 PM Reply   
That ellipse theory is off....you're better off just using the area of a square for your face. (9*6) because that'll give you the actual approximate surface area hitting the water. if you use the ellipse equation, you're getting the entire surface area of your head hitting the water, when you really just want the surface area of your face. if that makes sense. so you're looking more at 108 tons of force. I could be wrong though. And i dont know if that article/ad/psa factored in the "give" that the water has or not. I find it hard to believe the 4,000 psi number.

edit: the ad doesn't say PSI anywhere, it just says 3000 lbs of force for your entire body when it hits the water. that number seems a bit more sensible to me
Old    Jay T. (wakebrdjay)      Join Date: Apr 2008       09-01-2010, 5:44 PM Reply   
Yeah my second post is directly from the mag.
Old    Baitkiller (baitkiller)      Join Date: Jan 2010       09-01-2010, 6:08 PM Reply   
108 tons in my face hurts bad enough.

I think I may change my user name to: "Concussion Kid"
Old    Seahawks #1 Fan Robert T (cwb4me)      Join Date: Apr 2010       09-01-2010, 6:12 PM Reply   
i don't need the math to tell it hurts.i have nerve endings for that. LOL
Old    Adam Holdsworth (holdsworth)      Join Date: Jan 2010       09-01-2010, 6:34 PM Reply   
For some reason I'm going to give a serious answer... I hate being an engineer haha

Really, all you need is the height at which your center of mass reaches at it's max, and some sort of multiplication factor of the hardness of the water at that speed (ie, concrete would be a factor of 1 since it's, well, hard... even though it's hard, the water would be a factor of, say, .65)
Old    Art (rallyart)      Join Date: Nov 2006       09-01-2010, 8:30 PM Reply   
Ride in fresh water, it's not as dense.
So you can figure you are going about 40 mph across the wake. That varies quite a by how hard you cut.
The maximum force is also determined by the deceleration time to slow down. You get rid of the energy of the motion with a relationship of force and time.
Old    Joe (ilikebeaverandboats)      Join Date: Jul 2007       09-01-2010, 8:51 PM Reply   
lots of integrals need to be done to get your exact number .............right? To account for every possible distance from the edge of the board? or integrate some function from chin to top of head?? what would the function be tho??
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-01-2010, 8:55 PM Reply   
Just rig an accelerometer to your head...head out...have your driver make a turn in the boat...swing out and and do a mach speed butter slide like Murray does...then just ease your toes in. After your friends revive you...check the G meter.. As a B.S. Mech Engineering, I think this would be the best way for me to watch you figure this out. I can even take some good pics for you.

Actually, this is a very hard question. A lot depend on how hard you hang up an edge. When you catch a TS or HS edge....your feet & board stop, but you continue forward. If you don't let go of the handle...as you arc down, your acceleration rate increases. The trigonometry of your CG relative the the pivot point means that your angular velocity increases at an increasing rate right up till you hit the water. In addition, the force of the 'quarter spin' to faceplant stretches out your body...making your head strike worse. There is really no way to calc this when you hang an edge up....

So get an accelerometer and go plant your face.

Last edited by kitewake; 09-01-2010 at 9:00 PM.
Old    doctor octagon (dococ)      Join Date: Mar 2002       09-01-2010, 10:13 PM Reply   
Even if it were possible to somewhat accurately estimate a range of values within an acceptable margin of error, which I believe might be prohibitively complicated due to the number of unclear interacting variables, still I'm just curious what would be the point of knowing? And honestly I mean no disrespect, just wondering why you are wondering?
Old    Tim A (timmo)      Join Date: Nov 2009       09-02-2010, 5:03 AM Reply   
Quote:
Originally Posted by kitewake View Post

So get an accelerometer and go plant your face.
Best advice on WW ever
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 5:55 AM Reply   
here is an overly simplified calculation that makes a lot of assumptions...force = mass X acceleration...mass of your head = 8 lbs (from jerry mcguire)...acceleration = the change in spead of your head over a given period of time....when you catch your edge, the board stops and your head rotates around your board and the same speed you were traveling (23MPH) until it hits the water and abruptly stops (decelerates to 0 MPH)...we have to estimate the time it takes your head to stop (~.1 seconds??)...if it stops in .1 seconds, the accelertion (deceleration) is ~ 337feet/s^2...the force would be ~83lbs...of course this makes a lot of assumptions...
Old    Sam Hanna (samhanna)      Join Date: Sep 2009       09-02-2010, 7:06 AM Reply   
Nickbot hit the nail on the head.... well mostly. You only accounted for the linear speed at (23 mph), whereas if you board planted it would be a rotational acceleration which then takes the persons height into affect and utilizes it as the radius. This would be used to calculate the actual speed the persons melon were traveling when it hit the water, which would be faster than 23 mph
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 7:52 AM Reply   
i disagree...the board stopping does not cause any angular or tangential acceleration...it only changes the direction of the velocity...there would be centripital acceleration, of course, but no tangential acceleration until you hit the water...also the units for angular acceleration are different (useful for calculating torque, but not force)...i suppose there would be an acceleration due to gravity as the head starts to fall (32.3 ft/s^2) that would give another 8lbs ofimpact force...so, we are at ~90lbs of impact force...that seems reasonable to me...
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-02-2010, 8:12 AM Reply   
Well if you want to throw in another calculation... Take into account surface tension, naturally flatter water (butter) is going to have a higher surface tension than water that has some chop in it; therefore making a faceplant in "butter" much more painful. The more surface tension you account for = the faster your head stops = more force... correct?

I guess there are a whole bunch of variables here and we could go in circles forever...
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-02-2010, 8:15 AM Reply   
I might add that this is pretty entertaining... I'm an engineer and this is much more fun than what i do on a daily basis!
Old    Jonathan Bay (john211)      Join Date: Aug 2008       09-02-2010, 8:16 AM Reply   
oops ... my ellipse formula is wrong. It's 1/4th that. Anyway, my post was not serious.
Old    Adam Holdsworth (holdsworth)      Join Date: Jan 2010       09-02-2010, 8:30 AM Reply   
Doh! I didn't think of it as an edge catch.

In the event of an edge catch, wouldn't it be the same force as coming to a stop from ~23mph? (board stops, head keeps going until impact, but assuming a "perfect" pivot of the body)

@Christopher Roche, you're right on that. Just like in diving practice, they will churn up the water with air jets where they land so when trying new things, they don't fail completely.
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-02-2010, 8:36 AM Reply   
Ya know going back... Its funny how some people can sound like complete idiots in some threads, then come into another and some sound crazy smart. I read some pretty "impertinent" words in here... ha
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-02-2010, 8:42 AM Reply   
I thought these would be helpful!
Attached Images
  
Old    Alek Emery (acerock88)      Join Date: May 2008       09-02-2010, 8:43 AM Reply   
You could probably try to get a better estimate of the head's velocity as it hits the water by taking the original horizontal velocity and adding to it the speed gained from the change in its gravitational potential energy. It shouldn't be much, and it does not take into account air resistance, but it might help for getting a better estimate.
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 9:17 AM Reply   
i don't know why i assume edge catch...i guess that is what i associate a face plant with...the most important factor regarding the severity of the faceplant is your speed (mostly related to boat speed...but influenced by how hard you cut, etc....)...if you are talking about a face plant from a wake jump...say you cut in and travel at 35MPH thrrough the air and then go horizonal so your head is 6 feet off the water it will accelerate another 8MPH as you fall to the water for a total speed around 43 MPH...which would increase the impact force to ~160lbs...of course, this is over simplifed as the directions of the velocity are defferent and you would need to calculate the velocity vector in the direction you would be traveling...it also assumes you stop in .1 seconds which might not be so reasonable...if you double or triple that time the impact force is halved or thirded (??) or whatever...
Old    Jeremy (wake77)      Join Date: Jan 2009       09-02-2010, 9:19 AM Reply   
"i disagree...the board stopping does not cause any angular or tangential acceleration"

I disagree. The board would stop providing a pivot point in which if you were to calculate the speed, your head would be accelerating faster than, say your abdomen. Radius would play a factor, because your body is rotating around a fixed point (your feet and board). So:

Angular acceleration = Change in angular velocity / Total time

I think it is flawed to assume that you would be traveling at the same speed as the boat. The only way this would be accurate would be to step from a platform that is traveling the same speed as the boat and immediately digging your toes in. Even then, you have deceleration (you would still slow down slightly) before the edge caught.

In my view, the only accurate way would be to take the mean of about 100 W2W edge catches (the initial conditions would have to be identical).

But Kitewake probably has the best way to test it.
Old    Sam Hanna (samhanna)      Join Date: Sep 2009       09-02-2010, 9:20 AM Reply   
To not get too technical. If you drew a FBD of this your velocity would be in the "+"X direction and your acceleration would be in the "-"X direction as a form or friction from the water. Your head slamming into the water would in the "-"Y direction and the surface tension and density of the water would be in the "+"Y direction. The acceleration from falling would only be a resultant in the X direction and therefore technically have no impact in the Y direction which is what causes the head trauma. What causes the acceleration in the "-"Y axis would be the force from your board stopping on the X axis at a lower point than the velocity of the tow rope, which would act as a lever causing rotational acceleration into the negative "Y" direction. You would have to take a moment at the board which would then become Moment = Force X Distance, with the distance being from the board to the pull from the boat.....

My guess is that there are less of you that can understand what i just wrote on this forum than I have fingers on one hand.

Last edited by samhanna; 09-02-2010 at 9:23 AM. Reason: spelling
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 9:28 AM Reply   
don't confuse angular acceleration and angular velocity...you are correct that the angular velocity of the head would be greater than that of the abdomen...but the edge catch does not cause any tangential or angular acceleration (centripital yes)...think of driving your car at a constant speed and then you take a 90 degree corner...do you speed up?? of course accelerometer is the best way...just trying to get an approximation.
if the boat is traveling 23MPH and you are connected to the boat via rope/handle...you are also traveling 23MPH...edge catch usually happens while you are still holding the handle, hence the assumption...
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 9:36 AM Reply   
now i'm thinking your guys are on to something...your angular velocity is 0 when travelilng in a straight line...when you start rotating there IS angular acceleration...you could use that to back out tangential acceleration and then force...
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 9:37 AM Reply   
man, i'm bored today...
Old    Seahawks #1 Fan Robert T (cwb4me)      Join Date: Apr 2010       09-02-2010, 9:39 AM Reply   
this is all over my head. but i'm only 5'6' and i ride the short bus.LOL
Old    Sam Hanna (samhanna)      Join Date: Sep 2009       09-02-2010, 9:40 AM Reply   
What kind of engineer are you Nick? I am a Civil Engineer in Texas
Old    Jeremy (wake77)      Join Date: Jan 2009       09-02-2010, 9:51 AM Reply   
"think of driving your car at a constant speed and then you take a 90 degree corner...do you speed up??"

You can't compare that to an edge digger. You would have to think of it as you are driving at a constant speed, you hit a pothole that causes the car's rear end to rotate around the front end. (the car's linear velocity becomes zero). The rear bumper of the car as angular acceleration in relation to the pot hole (with the pothole being the center of the circle with radius L (length of the car).
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 9:54 AM Reply   
if you back it out as i mentioned above...that angular acceleration would add ~ 36lbs to the impact force bringing the total to ~125lbs (or 86lbs if your head stops in .2s)...sam, i'm mechanical in MI...
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-02-2010, 9:55 AM Reply   
that's a big f'n pot hole hahaha!!!
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-02-2010, 10:55 AM Reply   
How about this.... 23mph + TS face plant = Really BIG Headache and Nasal Congestion (no matter what variables you throw in)
Old    Francis Debelo (theanimal)      Join Date: Jun 2010       09-02-2010, 11:23 AM Reply   
LOL... I just read all of this and now I have a headache
You guys are too much for me...
Old    doctor octagon (dococ)      Join Date: Mar 2002       09-02-2010, 11:51 AM Reply   
I'm still trying to figure if this is all mental masturbation purely for entertainment purposes, or is there some reason he wants to know.
Baitkiller, is there some reason you want to know?
Old    Baitkiller (baitkiller)      Join Date: Jan 2010       09-02-2010, 1:42 PM Reply   
No hidden agenda, the amount of threads on this site about broken bodies and my own personal experience had me pondering the amount of force we are messing with.
This is not a helmet thread, or a CGA thread or save the manatee or Piping Plover thread. Just wondered how hard your head hits the water when the board stops in full edge load. Launching or landing.

So do we know? Or do I have to strap a meter on the melon and take one for the team?

Thanks guys.
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-02-2010, 1:50 PM Reply   
hahahaha.... Sound like "the ladder" is our only option. Now who's gonna take the hit?
Old    doctor octagon (dococ)      Join Date: Mar 2002       09-02-2010, 2:43 PM Reply   
Just wondering because in terms of head injuries, the type/quality of force can be as important, or moreso, compared to the simple magnitude of force in determing types, extent, amount, complexity, implications of damage, etc. to the brain. Example, straight on blow to side of head is different from straight on blow to forehead, is different from blow combined with twisting motions, is diffetent to blow combined with abrupt stopping of momentum, etc. So even if it were possible to determine the magnitude of force, it really doesn't tell you anything definitive or predictable about the potential damage done within your cranium's gelatinous innards. But indeed it might be cool sometimes to tell people that your head smacked the water with x tons of force.
Old    LEE DANEILS (hyperlite)      Join Date: May 2009       09-03-2010, 6:43 AM Reply   
hahaha
Old    Jeremy (wake77)      Join Date: Jan 2009       09-03-2010, 7:16 AM Reply   
Bait, I believe that the consensus is, it is really too complex to simply plug into an equation and get a result. Nickbot was able to offer an approximation, which seems to be in the ballpark, but truth is, an accelerometer would probably be the only way.
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-06-2010, 12:15 AM Reply   
Nicks numbers are not even in the same zip code as the ballpark.

One of the first common sense sense questions to ask yourself, as an engineer, is does the answer even make sense.

"~90lbs of impact force...that seems reasonable to me... "

Really? Seems like an awfully low number. Assuming about 55 square inches of frontal area...that is less than 2 psi.... Seems WAY low.

The average G force, to the skull, experienced by a boxer when struck solidly is 50-60 Gs. Football players often experience over 100 G's. The range of acceleration thought, by medical researchers and physicians in the field, to cause a concussion or loss of consciousness is from 60-150 G's...depending on the person. Lets just assume wakeboarders have weak chins...and call the threshold 60. We all know that wakeboarders get knocked out from time to time by hard hits when they catch an edge. We also know that the average human head weighs 9-11 lbs. So a really bad edge catch is capable of knocking you out...and thus decelerating your skull at a minimum of 60 G's. 60 x 10 = 600 lbs. That is the reasonable range just by working backwards from proven medical research.

The numbers stated here are well below the realm of what is reasonable. Nikbots assumptions and methods of calculation way way off.... 90 pounds...I wish.

Last edited by kitewake; 09-06-2010 at 12:20 AM.
Old    Alain (ak4life)      Join Date: Nov 2003       09-06-2010, 10:38 AM Reply   
As a competitive kickboxer in my youth, I can confirm that head impact from a good edge catch wakeboarding can ruin one's day as effectively as taking a solid punch or kick to the head.
Old    Alain (ak4life)      Join Date: Nov 2003       09-06-2010, 12:00 PM Reply   
I don't have any science to contribute, just a crapload of inferences, but heck, this is a forum, not a Ph.D thesis, so here we go..

There was an episode of Sport Science (1) which compared impact from big things moving slowly (sumo wrestlers) with small things moving fast (a punch), measured Rampage Jackson hit at 1800 PSI. There's some controversy there regarding Quentin's imperfect punching technique (2), but it was on TV so it must be true, therefore we accept it as fact.

I'm certain that a properly executed muay thai style roundhouse kick could produce at least twice as much force as a punch, and a solid edge catch at 30-40 mph completely stopping the board and swinging the rider like a pendulum, causing the tip of the pendulum (which so inconveniently happens to be the head) accelerate much faster still, producing impact that has to be greater than either a punch or a kick, so a claim of several thousand PSI doesn't strike me as impossible.

Perhaps someone could petition Sport Science or Myth Busters to take this on. ;-)

(1) http://www.youtube.com/watch?v=jzYMX_3K_xE&eurl=
(2) http://www.boxingforum.com/boxing-fo...psi-punch.html
Old    Alain (ak4life)      Join Date: Nov 2003       09-06-2010, 12:09 PM Reply   
http://www.youtube.com/watch?v=maQINqPI7S0
http://www.youtube.com/watch?v=C2JhhzYqaB8
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-06-2010, 2:30 PM Reply   
Quote:
As a competitive kickboxer in my youth, I can confirm that head impact from a good edge catch wakeboarding can ruin one's day as effectively as taking a solid punch or kick to the head.
Kicks to the head...that explains a lot, Alain.

But your gut inference about the pendulum/pivoting effect is correct. When you are in the air (if you are not doing an invert of spin), all (if you hold a static position) of your momentum and kinetic energy is due to translation/linear motion. When you catch an edge, however, a rotational constraint is added, and this complicates things greatly. You now have pivoting action, and parts of your body (feet...legs...pretty much anything below your center of mass) slow down....but where does all the energy your body has due to translation (moving through the air) go? It goes to INCREASING the velocity in other parts of your body...above your center of mass.

The only way you can catch an edge, do a face plant, and not have your head hit at a much faster speed than you are traveling is if 100% of your body mass is in your head! In that case...and only in that case, would your head strike the water at the same speed it was translating (actually...it would strike a bit faster...due to a conversion of potential energy to kinetic energy due to the acceleration from gravity..)

A good analogy would be a trapeeze acrobat flying horizontally through the air...and then hooking his or her feet on a fixed bar...and going from a horizontal flightpath to a spin constrained by that bar/pivot. Because your head is located way beyond your center of mass, your angular velocity is always accelerating through the first 90 degrees of rotation.

In wakeboarding...this is made even worse if you don't leg go of the handle. This is because the handle is traveling at a fixed velocity...pretty much no matter what force you as a rider can apply to it. There is so much going on here...

A good example of this from an academic text is from the rotational motion chapter in Fundamentals of Physics, Halliday and Resnik. An example of linear bodies falling in rotation is presented. When a tall industrial stack is brought down by placing explosives at the base, it will usually fracture in the middle part way down.

To quote:

Quote:
Before rupture, the chimney is a rigid body, rotating about an axis near its base with a certain angular acceleration, alpha. From Eq 17, the top of the chimney has a tangential acceleration a(subt) given by alpha x L, where L is the length of the chimney. The vertical component of a(subt) can easily exceed g, the acceleration of freefall. That is the top of the chimney is falling downward with a vertical acceleration greater than a freely falling brick.
This is only with free fall under gravity! Add pre-existing translational motion, and a constant linear/horizontal velocity constraint, the effect is even more exaggerated.

Lots of people here trying to apply fancy engineering principles without even identifying or understanding the basic free body physics. At its heart...this is a freshman year physics problem (but a challenging one...) before it is an engineering problem.
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-06-2010, 2:33 PM Reply   
Here is a pic demonstrating the loads that act in a body falling about a pivot when the center of mass is not at the end. The acceleration at the end is a multiple of acceleration of the center of mass. This sets up loads that cause the rigid body to fracture.
Attached Images
 
Old    Joe (ilikebeaverandboats)      Join Date: Jul 2007       09-06-2010, 2:38 PM Reply   
You guys are above my head at this point. Im working on my statics homework right now haha.
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-06-2010, 2:41 PM Reply   
This is all the explaining that is needed....

http://www.youtube.com/watch?v=xE6YxkNU4ac

Looks like about 80 G's to me!
Old    Alain (ak4life)      Join Date: Nov 2003       09-06-2010, 10:06 PM Reply   
OMG, that faceplant was so bad. Poor Tanisha...
Old    Tom N (SangerTom)      Join Date: Aug 2010       09-06-2010, 10:29 PM Reply   
I know I think I understood what I thought you said. But I'm not sure I realize what you said is not what you meant.
Old    Nickbot (nickbot)      Join Date: Feb 2007       09-07-2010, 5:58 AM Reply   
brant, i have to take issue with a few of your points.
1) surface area of the head : I don't think it's reasonable to use the projected area of the whole head, perhaps the projected area of the forehead, nose, and chin is more appropriate...more like 8-10in^2
2) 60 g's = 60 X the acceleration due to gravity (32.3ft/s^2) or 1938 ft/s^2....X 10 lbs = 19380lbs....not 600lbs...check your math...
3) i believe 60 g's is too high an assumption for this case...car crash generates upwards of 30g's in the head...blue angles generate ~ 6g's...i don't thing an edge catch is in this range...
regardless, my previous estimate of 125lbs may be low...but, i think that has more to do with underestimating the time it takes your head to stop (.1s...maybe more like 30ms??), and underestimating the weight of the head (8lbs vs. 10lbs) than bad theory. if we assume a 10lb head and 30ms to stop (~2g's)...the force would be more like 500lbs...more reasonable?? drop a 15lb weight on your face...does that feel like your last edge catch??
Old    Christopher (Cajun_Misfit)      Join Date: Jun 2010       09-07-2010, 7:48 AM Reply   
I think I'm gonna side with Nick here... I could see ourselves taking that kind of blow (500 + lbs) if we were boarding on asphault. The fact is water somewhat cussions the blow, so you really cant compare a faceplant in water to : a car crash, punch from Rampage, or a so-called round house kick from Chuck Norris... That being said, it takes 16 - 196 lbs of force to crush the human skull depending on size/angle/etc... So if we are taking 500+ lbs faceplants, we as wakeboards are as crazy as everyone thinks.

Now we have more variables to consider!!!
Old    Alain (ak4life)      Join Date: Nov 2003       09-07-2010, 12:13 PM Reply   
Quote:
Originally Posted by Cajun_Misfit View Post
The fact is water somewhat cussions the blow, so you really cant compare a faceplant in water to : a car crash, punch from Rampage, or a so-called round house kick from Chuck Norris...
It's been demonstrated that faceplants can cause loss of consciousness and concussions, just like any other sufficiently hard impact, so I guess I don't understand why they can't be compared?

Sounds like the challenge is calculating the exact force of a faceplant, since there are so many variables involved. So we're right back to the best advise ever given on wakeworld:

Quote:
Originally Posted by kitewake View Post
get an accelerometer and go plant your face.
Or get a $150K crash test dummy and figure out a way to consistently plant his face to produce a large enough sample to be useful.

Else, I personally think it's not unreasonable to say that a wakeboarding faceplant can yield forces comparable to a solid punch or kick to the head or even a 35 mph car crash (1).

(1) http://www.youtube.com/watch?v=j4SQzbAFNmo&NR=1

Last edited by ak4life; 09-07-2010 at 12:22 PM. Reason: just because
Old    Jeremy (wake77)      Join Date: Jan 2009       09-07-2010, 7:33 PM Reply   
"...and thus decelerating your skull at a minimum of 60 G's. 60 x 10 = 600 lbs."

You had me going until you posted this gem. It totally killed your cred.
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-08-2010, 4:30 PM Reply   
Really Jeremy...

remember...this was the force acting on the HEAD....and the head weighs 10# +/-.

Lets do it in SI units....that way I don't get confused by the pound force vs pound mass vs slug thing

Ave human head = 4.5 kg (4.5*2.205 = 9.92...close enough)
1G = 9.8 m/s^2 (32 feet per second squared....)

F=MA
1 Newton = 1 Kg*m/s^2

Again...common sense. It takes a 60 G impulse to knock you out. This has been well documented. (G's in a plane are steady state...you lose consciousness due to blood flow...concussions, etc are due to impulses...totally different)

60G = 588 m/s^2

The force to decelerate your skull at 60G, and be in the ballpark of knocking you out is 2646 Newtons.

If we do the pound force conversion...we have 1 lbf = 4.45 Newtons.

2646/4.45 = 594.....

Hmmmm...pretty close to 600... let's call it a rounding error..
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-08-2010, 4:38 PM Reply   
Some more food for thought....

http://www.impactlab.net/2006/01/22/...tects-g-force/

Quote:
The helmets have measured more than 33,000 hits on the North
Carolina team, and more than 250 of those hits had a force greater than
100 Gs. That is equivalent to slamming into a brick wall at 25 miles
per hour.
Or you can go read these two studies...

Guskiewicz KM, Mihalik JP, Shankar V, et al. (2007). "Measurement of head impacts in collegiate football players: Relationship between head impact biomechanics and acute clinical outcome after concussion". Neurosurgery 61 (6): 1244–52; discussion 1252–3. doi:10.1227/01.neu.0000306103.68635.1a. PMID 18162904.

Gever D (December 7, 2007). "Any football helmet hit can cause potential concussion". MedPage Today, LLC. http://www.medpagetoday.com/Neurolog...rology/tb/7625. Retrieved 2008-02-27.

They both put the concussion threshold range at 70-75g's.

So explain to me please why wakeboarders can suffer a consussion at 9-12Gs (per Nick)....when most other humans keep the lights on up to 70-75?

You can also take to heart Kyle Schmidt talking about learning a raley...

Quote:
This trick is no joke. In my 15+ years of coaching I've done seizure resuscitation on two people and seen many concussions. I myself separated ribs multiple times during the learning process. This isn't meant to scare you, just to make sure you take the safest route possible.
Not the sort of result that come from 90-126 lbs...

Last edited by kitewake; 09-08-2010 at 4:45 PM.
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-08-2010, 5:04 PM Reply   
The pound is a unit of force....when you do F=MA in Imperial units...you have to use slugs. The Slug is a mass that accelerates by 1 ft/sec2 when a force of one pound-force (lbf) is exerted on it. Therefore a slug has a mass of 14.5939kg. The head weighs about .3 slugs.

F = Force
M = Mass
A = Acceleration

If you use pound force for F=MA, you are using a force to calc a force...and up with a way high number....common mistake. See my previous SI derivation above. Imperial units suck for this reason. When ever doing any dynamics calcs...I like to convert to SI just to double check....

32 *60*.3 = 576

Who ever came up with Slugs...anyway?
Old    doctor octagon (dococ)      Join Date: Mar 2002       09-08-2010, 5:20 PM Reply   
That picture reminds me of something else.
Old    Brant Williams (kitewake)      Join Date: Jul 2007       09-08-2010, 5:36 PM Reply   
A quick back check. You hit an object at 35 mph (15.65 m/s). You decelerate at 60 Gs (588 m/s^2). How long will is take you to stop? Only .0257 seconds. So what seems like a very high force...acts only for a very short period of time. The distance covered during constant deceleration is still not trivial. It works out to about .216 meters....or 9".

If you hit at 35 mph...and decelerated a 6G...how far would you take to stop. About 2 meters under constant decceleration, taking .26 seconds...which is a LONG time. Since we are talking about velocity normal to the water.....that does not seem reasonable. The water is a lot harder than that.

I stand by established medical research and recent experience. 60Gs, which for a 10# head is about 600 pounds of force....albeit only for a fraction of a second.
Old    Baitkiller (baitkiller)      Join Date: Jan 2010       09-08-2010, 5:58 PM Reply   
Brent I almost understood that.

I think I'll read it again tomorrow morning.
Old    Landan Luna (landowakettu)      Join Date: Nov 2009       09-11-2010, 10:03 AM Reply   
I really hate that I know whats going on right but it was greatly entertaining! Im currently finishing up a BS in Mechanical Engineering, all the assumptions and data seem viable to me, although shouldn't we account for the surface tension of the water, on a butter day it would be rather high as compared to a blown out day? I know it may seem trivial but I think it could apply more pressure to the "melon". Also you've got to consider the temperature of the water on certain days...

Surface Tension: force needed to change the surface of a liquid (not exact definition but will do)

Temperature
(oC) Surface Tension, σ (N/m)
0 0.0756
10 0.0742
20 0.0728
30 0.0712
40 0.0696
50 0.0679
60 0.0662
70 0.0644
80 0.0626
90 0.0608
100 0.0589

And those numbers are with air as the medium contacting the water, it could be slightly different when taking into account human skin. Just food for thought...

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