# Force caused by a bullet in a bone

1. Nov 26, 2013

### danielamartins

Is it possible to calculate the force caused by a bullet in a bone, knowing the velocity of the bullet when fired, its weight, and the bone's thickness?
If so, could you explain it a bit?
I need to create a sort of exercise, so I wanted to do something involving a bullet and a body. Therefore, I could add some details/info if necessary...

2. Nov 26, 2013

### Staff: Mentor

An easy model that will get results that are order-of-magnitude sensible is to assume that the bullet decelerates at a constant rate until it either comes to a stop or exits the other side at a slower speed.

Now the thickness of the bone gives you the distance traveled, the initial speed and assumption of constant deceleration gives you the average speed that distance is traversed, from that you get the time of passage and the deceleration. Now the mass of the bullet and $F=ma$ will see you home.

No doubt the forensic pathologists have waaaay more sophisticated models.... But not necessarily the case that a more sophisticated and accurate model will produce any more insights.

3. Nov 26, 2013

### danielamartins

Thanks, but how can I calculate the acceleration?

4. Nov 26, 2013

### Staff: Mentor

You know the change in velocity and you can calculate the time over which that change happens. For example, if a projectile moving at 20 m/sec is brought to a stop over a distance of 1 meter...

Its average speed through that meter is 10 m/sec (average of 20 and 0, assuming constant deceleration) so it take .1 sec to cover that one meter. Because the speed goes from 20 m/sec to 0 m/sec in that .1 sec, so the deceleration is 200 m/sec2.

5. Nov 26, 2013

### danielamartins

Oh thanks! I was making it more difficult than it actually is. I'll try to do all the calculations and then, I'll post them here. If u could take a look I would appreciate it ;)

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