Science Buddies: "Ask an Expert"

Hi I was wondering if someone could explain to me a little better what g force is.

I know that a g is one times the force of gravity. So for example, if you are pulling six g's you are experiencing six times the force of gravity.

What confuses me is the concept of impact g's. For example, a football player may take as many as 100g's to the head. I know that they occur for a very short duration, and that is why they do not kill him.

I would really like to have the difference between normal g forces and impact g forces clarified. Also, is there a way calculate the impact g's of an object by using its mass, speed, etc.?

I would really appreciate your help ASAP.

Thanks!

Please look up various force equations and explainations of them to understand them and how to add and subtract force vectors as a starting point.

One of the simplest Force formulas is F = M x a (Force equals Mass times Acceleration). The gravitational constant "g" is the acceleration constant for graviataional forces so F = M x g when the acceleration is caused by gravitational forces.

Acceleration is defined as the change in Velocity with respect to time (dV/dt in calculus terms). In an impact, the velocity can change very rapidly so you can easily get instantaneous forces that are extremely high. If you have had calculus or pre-calculus, then you should be able to understand taking the limit of dt (change in time) aproaching zero will give you an infinite value. If not, then divide 1 by 1, then by 1/10, then by 1/100, then by 1/1000, etc and see what happens to the result.

In reality, there is some elastic nature in all materials that allow the materials involved to initially bend which means the deacceleration time interval never actually reaches 0; however, it can happen very quickly and you can easily get factors of 10**3 to 10**9 times the pre-impact velocity. Predicting and measuring impact forces is an in-exact science because a small error in a small number in the denominator makes a big difference in the result.