I think you are misunderstanding the information you have found.

First. Football concussion research looks at the G forces acting on the skull at the surface of the skin, not the forces acting on the surface of the helmet.

The fall into a chair causing 10 G's sounds very high. If the chair is rigid, and one lands with the back arched (straight vertebral column), and there is minimal absorption through the back side, the G forces could be that high as they are transmitted up the spine. But, a cushioned chair and/or a normally curved back will greatly reduce these forces.

The tennis ball number is also misleading. Is this 3 G's acting on the tennis ball or 3 G's acting on the skull. The fact that a tennis ball distorts means the G force is reduced.

*admin edit*

Regarding sneezing, there is a whiplash effect causing G forces plus a pneumatic pressure in the sinuses.
Here is a good but complex explanation of calculating G forces. http://www.decodedscience.com/mythbu...alling/26999/2

Regarding the head-on vehicle collision. There are far too many variables to even begin to answer that question without seeing the damage to the vehicles (distortion) and movement of the vehicles after contact and making assumptions of occupant movement inside the vehicle. Even the insurance companies do not often try to make these calculations with highly trained accident reconstruction specialists.

When G forces are measured, there are 3 key factors. Speed before collision, speed after collision and the amount of time for that change in speed. The change in speed over time is either acceleration or deceleration and can be converted to G forces. If there is a complete stop, then deflection can be used in place of the time for that change in speed.

That tennis ball is traveling at 55555 mm/sec. It would likely deflect by 12 mms or more. But, if the skull it hits moves back 6 inches (150 mms) during the contact, that movement is part of the deflection. So, the deflection would be 162 mms. The formula for G force is V1 squared minus V2 squared divided by 2 times distortion divided by acceleration of gravity. So, 55555 squared minus 0 squared divided by 324 divided by 9800. That means the tennis ball experienced 972 G's. But the head did not experience the same G force since it started at 0 velocity and ended at X velocity and moved 6 inches (150 mms) during contact with the ball. That calculation is far more complex. This is where the mass of each object would be needed to calculate the G force to determine velocity X. Even so, assumptions would need to be made.

So, hopefully, you see that it is extremely difficult to calculate these forces.

The tennis ball hit me on the forehead, while i was standing at the net. As far as i can remember, my head went back just about one inch(the ball weighs only 58 gramms).

I see how difficult it is to calculate the g's. But i think it is quite interessting to figure out how much is actually necessary to cause a concussion(for instance, everybody around me told me that a tennisball has not the enough force to cause TBI, but in fact it has)

When we say for instance that 10 g's are necessary, does this mean that the brain hits the skull only when a force of 10 g or more is reached or does it hit the skull also on lower g's, whithout resulting in a concussion? The question is interessting, because sneezing or twitching makes me feel dizzy for a while - is that because the brain touches the skull?

(Here is the link which i wanted to add in my last post www.braininjury.com/injured.shtml )

And here i found the tennis ball calculation:

http://tt.tennis-warehouse.com/showthread.php?t=357202

That tennis ball calculation is wrong, He forgot to square the 55.55 m/sec/sec. Plus, he does not account for the time the racket spends pushing the ball in a powering through stroke. Others suggest the ball was in contact with the racket for 48 cms. As he said, he did not stay at a Holiday Inn Express nor is he a physics expert. If the ball was in contact for only a short distance, the 2200 G's would be the answer. At 48 cms of contact with the racket, the G's would be 320.

The ball that hit you was not going 200 km/hr (55 m/sec). A common tennis serve is 34 m/sec as the ball leaves the racket. By the time it crosses the net, it has lost a lot of speed, maybe to 25 m/sec.

At 58 grams, the tennis ball does not have much effect on a 5000 gram human head attached to a heavier body. According to my calculations, a 5000 gram head would move only about 5 inches when struck by 58 grams at 25 m/sec. The G's of that hit would be about 50 or maybe a bit more. It would move less if there was an effort to limit any movement. In that case, the G force would be higher. Sounds like enough G's for a concussion.

The numbers in the braininjury.com web site are not supported by either research or common physics. It would take quite a plop to get 10 G's. It would take a 20 inch fall with only 2 inches of cushion distortion to get 10 G's. I don't know of many butts that are 20 inches higher than the seat of an easy chair with only 2 inches of cushion distortion. Mine distorts about 4 inches. This site is an attorney's web site with a lot of 'selling to the jury.'

There is one more thing that bothers me. I've read that some people got concussions from hitting there head (very) lightly against a hard, non moving surface(wall, table). It happens unfortunately from time to time to probably everyone(you can't be cautios enough)

Back to our g calculations, how can such a light bump ever cause a concussion? I mean there is not enough acceleration of the brain that could reach the required g force, even though the deceleration is of course higher.

Those things you read are likely not accurate. A light touch against a hard object or wall would not cause a concussion. It may cause an anxiety response. A very sensitive brain may sense a slight 'dinger.'

You guys need to think more about the heads structure in your attempts at calculations and ponderings.

Different substances absorb force in different manners, as does structure diffuse. IE Skin and bone behave very differently under force. And then there are different strengths and weaknesses in the scull. Then an understanding of where nerves/blood vessels lay. Where the impact is will serve to antagonise/mitigate the blow.

If you have a hard tap to the right place on the head it is possible, as the flesh/skin would becomes inflamed and starts to heal, you may have a few burst blood vessels and if this is over a nerve the inflamation could cause the signals to get muddled for a few weeks (or much longer if the actual nerve is damaged, with greater force).

Ash,

We are not discussing surface or skin confusions. Yes, they can be painful but do not relate to the concussion forces that we are discussing.

Mark, even you said in one of your older posts that light hits can cause a concussion.

http://neurotalk.psychcentral.com/thread82429.html

Nonetheless this is not the only source I found. I googled for a couple of minutes and saw quite a number of posts, where people experience concussion symptoms after a light bump(even without prior head injuries)

I don't excactly know what you mean with 'dinger'