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# Stopping a bullet in a solid watch

1. I'm trying to work out what thickness a solid of a given density would have to be in order to stop a bullet.

I can figure out the speed of the bullet, assumed to be constant then assuming the solid provides a constant deceleration then I could work out the thickness the solid wouid have to be by calculating the distance the bullet would travel before its velocity was 0.

I'm not too concerned as to whether or not the assumptions ive made are great. I would like to know how I could go about calculating the deceleration caused by the motion inside the solid, I get the feeling its quite simple but Im not certain how to go about it to be honest.

Probably missing something stupid but I'd love a pointer in the right direction!

Thanks
- Eremor
2. (Original post by Eremor)
I'm trying to work out what thickness a solid of a given density would have to be in order to stop a bullet.

I can figure out the speed of the bullet, assumed to be constant then assuming the solid provides a constant deceleration then I could work out the thickness the solid wouid have to be by calculating the distance the bullet would travel before its velocity was 0.

I'm not too concerned as to whether or not the assumptions ive made are great. I would like to know how I could go about calculating the deceleration caused by the motion inside the solid, I get the feeling its quite simple but Im not certain how to go about it to be honest.

Probably missing something stupid but I'd love a pointer in the right direction!

Thanks
- Eremor
Depends a lot on other material properties of the bullet and target
e.g. a very brittle material could be smashed and pushed out of the way without dissipating much energy.

different materials have different effectiveness in taking the energy out of a projectile hitting them.

e.g. these pumpkins turned out to be surprisingly tough despite being largely hollow - see how many the guy had lined up

whereas these tiles weren't

The bullet wasn't recovered in that video... and that chap always seems to show the bullet if he's able to recover it so I suspect it deflected out sideways with enough velocity left to take it a considerable distance.

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