# G force calculation of hitting the head

• freexd
In summary, without knowing the velocity of your head at the moment of impact or how long you were accelerating, there's little we can do. Can you put this in context for us? Were you in an automobile accident? The details may help us figure out some approximation.
freexd
Hello,
Could you guys please do me a favor and calc the g force of a 8.8lbs head that accelerates with 1m/s or 1.5m/s and than hits a solid metal objebt with the back of the head which moves 0.5 mm.

This is no homework. It happened to me.

http://arxiv.org/pdf/0711.3804v1.pdf

Here's a paper we wrote on the subject of head impacts.

Hitting stuff hard that moves very little is a bad plan.

There is some give in the scalp and some bending in the skull, but not much.

Accelerations can be high.

This looks very interessting but way to complicated for me.

I don't know how to do it

freexd said:
Hello,
Could you guys please do me a favor and calc the g force of a 8.8lbs head that accelerates with 1m/s or 1.5m/s and than hits a solid metal objebt with the back of the head which moves 0.5 mm.

This is no homework. It happened to me.

Without knowing the velocity of your head at the moment of impact or how long you were accelerating, there's little we can do. Can you put this in context for us? Were you in an automobile accident? The details may help us figure out some approximation.

freexd
Drakkith said:
Without knowing the velocity of your head at the moment of impact or how long you were accelerating, there's little we can do. Can you put this in context for us? Were you in an automobile accident? The details may help us figure out some approximation.
No I wasnt in a car accident. I wanted to look through a window and pulled the curtains back(not to the side). I ve overseen this big metal bar attached on the wall and leand my body and head back until it collided. The impact was moderate hard.

The velocity while hitting the object has to be 1 or 1,5 m/s. I think I did not decelerate before the impact. The distance when I started to move backwords was 30 cm. I cannot tell how long I was accelerating,

I'm not sure it's possible to get an accurate number then.

Drakkith said:
I'm not sure it's possible to get an accurate number then.
So the only thing that would be needed is how long I accelearated?

I calculated 0.6s

freexd said:
So the only thing that would be needed is how long I accelearated?

Even with that I'm not sure what we could really do. It's a complicated problem. But honestly I don't expect that the g-forces exerted on your head were very high. There's no way you were moving that fast.

Drakkith said:
Even with that I'm not sure what we could really do. It's a complicated problem. But honestly I don't expect that the g-forces exerted on your head were very high. There's no way you were moving that fast.

After rethinking this I would say youre right.

I needed approximately 0.5 s for a 30cm distance. So my velovity was 0.6m/s.

Now it should be doable? It os no problem when the calc is not 100% correct.

Now it depends on how fast your head decelerated. And that I don't really know how to find out. If we assume that it takes 0.27 seconds (the time of the collision in the paper linked in the 2nd post) then the deceleration is only 2.22 m/s2, which is less than 1/4 g. I expect that the time taken to come to a stop is different than 0.27 seconds, but I don't know by how much. Still, that should give you a decent estimate.

Drakkith said:
Now it depends on how fast your head decelerated. And that I don't really know how to find out. If we assume that it takes 0.27 seconds (the time of the collision in the paper linked in the 2nd post) then the deceleration is only 2.22 m/s2, which is less than 1/4 g. I expect that the time taken to come to a stop is different than 0.27 seconds, but I don't know by how much. Still, that should give you a decent estimate.
0.27s is far too long. It was a rapid stop as metal give not much room. I would drop this number down to 0.1s

About 50-60g would be requird for a concussion,
10-20g is a subconcuasive impact.

I am sure it is around 20g

freexd said:
0.27s is far too long. It was a rapid stop as metal give not much room.

freexd said:
I would drop this number down to 0.1s

That puts the acceleration at 6 m/s2, or just under two-thirds of a g.

Note that you can sustain an injury at much lower g-forces than commonly stated if the force is concentrated in a small area, such as when you hit your head on an metal bar.

Yes I only hit a small part of my head(more the edge of this thing)

So in summary we end up that it cannot be calculated.

At least an assumtion?

freexd said:

Drakkith look here please. They calculated much higher fores.

If you're referring to post #33, then it appears they've made a mistake with the units. Converting everything to meters (which is what you have to do) gives me 9.16 g's, not 91.6 g's. The calculated values in post #35 are also wrong. For the 0.5 mm deflection, the g-force is 0.19 g's, not 1.9.

freexd
Ah ok. You know certainly more like this users about physics.

So what is a reasonable value for my incident yesterday? I know physicians don't like estimations

Assuming your head is a rigid object, a velocity of 0.6 m/s, and that the bar deflects 0.5 mm, I get 3.7 g's.

That looks so little. The bump was mediocre intense. Now think how hard you have to hit your head to get 20-60g. Why did you take 0.5mm? How high are the gs when we reduce this to 0.1mm??

The nfl does reasearch on head to head collisions. Most of thestart at twenty and go up to 50 and more.

Drakkith said:
Note that you can sustain an injury at much lower g-forces than commonly stated if the force is concentrated in a small area, such as when you hit your head on an metal bar.

Where do you have this info from? Imagine the bar to be 4m long, 10cm wide and high. It hit me almost with the edge in the area where the ear ends a bit above.

Drakkith said:
Note that you can sustain an injury at much lower g-forces than commonly stated if the force is concentrated in a small area, such as when you hit your head on an metal bar.

With respect to brain injury, this is only true if the skull itself is compromised. More focussed forces are more likely to compromise the skull.

But with respect to brain injuries that occur without skull injury, it is the translational and rotational accelerations that matter, without regard for how concentrated the external forces and torques are on the head.

A Physics Forum is a poor place to attempt to diagnose a head injury. Google up the common symptoms and if you still think you may be injured, seek a medical diagnosis from a medical professional.

Dr. Courtney said:
With respect to brain injury, this is only true if the skull itself is compromised. More focussed forces are more likely to compromise the skull.

I was under the assumption that a blow to the head was able to cause injury without compromising the skull.

Dr. Courtney said:
A Physics Forum is a poor place to attempt to diagnose a head injury. Google up the common symptoms and if you still think you may be injured, seek a medical diagnosis from a medical professional.

That I agree with.

Drakkith said:
I was under the assumption that a blow to the head was able to cause injury without compromising the skull.

No doubt, but with closed head, blunt force traumatic brain injuries, it is the net rotational and translational accelerations that matter. The area of impact generating the acceleration is not relevant. These injuries occur because of movement of the brain inside of the skull and are essentially due to inertial issues. The skull is acting like a rigid body, and the brain and brain stem are a not-so-rigid body moving around inside the skull and getting damaged.

Last edited:
Dr. Courtney said:
No doublt, but with closed head, blunt force traumatic brain injuries, it is the net rotational and translational accelerations that matter. The area of impact generating the acceleration is not relevant.

I don't agree that the area of impact isn't relevant, but I'm not going to argue it here, as it would be off topic.

I think my skull was not injured, so the rotational and translational forces matter. With the provided data, where they high enough for an injury?

We can't diagnose injuries here at PF, sorry. If you're worried that hitting your head caused you injury, then please see a doctor. Thread locked.

## What is G force and how is it calculated?

G force is a measurement of acceleration that an object experiences due to the force acting upon it. In terms of hitting the head, it is the force that the head experiences upon impact. This force is calculated by dividing the change in velocity by the time it takes for the change to occur. It is often measured in units of "g", with 1g being equal to the force of gravity.

## What factors affect the G force of a head impact?

The G force of a head impact can be affected by several factors, including the speed of the impact, the angle of impact, the surface area of the object hitting the head, and the strength of the object hitting the head. Additionally, factors such as the density and elasticity of the object can also play a role in the force experienced by the head.

## How does G force impact the brain during a head injury?

G force can have a significant impact on the brain during a head injury. When the head experiences a high level of G force, the brain can be jolted or shaken, causing it to move and hit against the skull. This can lead to bruising, bleeding, and swelling, which can result in a range of symptoms and potential long-term effects.

## What is considered a dangerous level of G force for a head impact?

The level of G force considered to be dangerous for a head impact varies depending on the individual's age, health, and other factors. However, it is generally accepted that a G force of 50 or higher can result in severe injury or even death. It is important to minimize the G force experienced during a head impact to reduce the risk of injury.

## How can G force calculations be used in preventing head injuries?

By understanding and calculating the G force of a head impact, safety measures can be put in place to reduce the risk of injury. This can include using proper protective gear, avoiding high-risk activities, and designing safer environments. Additionally, knowledge of G force calculations can aid in the development of safety regulations and guidelines for minimizing head injuries.

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