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Lets talk Physics; Bullet Block Experiment.

Telryon

Telryon

Passed Driver's Ed
Location
Laurel, MD
Haha...I am an engineer for a living, so yeah...a little of both.

As for elastic/inelastic - you're right. I think this falls under the inelastic category. I assumed perfectly inelastic, but that's probably not 100% the case (I'm sure the bullet deforms/fragments on impact). Either way, though, conservation of momentum is still valid.
 
CodeB4U

CodeB4U

Go Kart Champion
Location
Houston, TX
Telryon said:
Haha...I am an engineer for a living, so yeah...a little of both.

As for elastic/inelastic - you're right. I think this falls under the inelastic category. I assumed perfectly inelastic, but that's probably not 100% the case (I'm sure the bullet deforms/fragments on impact). Either way, though, conservation of momentum is still valid.
Click to expand...

Well from what they said in the video the bullet stays in the block of wood. So the bullet has to deform and the wood has to deform also. There is no way either one can put or take mass without deforming. The caliber of bullet wasn't big enough to deform the wood by cracking/splinting the wood. The 22. cal. bullet just compressed the wood fibers...wait...just thinking about that makes more sense.... Compressing, is creating heat, heat is thermal energy, taking away energy, giving it the height is goes to. So if you hit it on the side of the wood, it's rotating, rotational is not free...so the thermal energy it takes to compress the wood and the rotational energy it takes to spin the wood is canceling each other out...giving it the same height. Reason we don't see that is cause we don't see thermal imaging...i bet if they did it with thermal camera, the block of wood shot in the middle will be warmer then the one that is rotating, Because the thermal is missing or is replaced by rotational energy in the wood shot on the side.

Maybe?

The wood is receiving all the energy the bullet is creating, but the wood is displaying two different types of energy. One (thermal) is not visible to the human eye. The other is rotational, which we clearly see.

I hope next week they do have a thermal camera.
 
Telryon

Telryon

Passed Driver's Ed
Location
Laurel, MD
CodeB4U said:
Well from what they said in the video the bullet stays in the block of wood. So the bullet has to deform and the wood has to deform also. There is no way either one can put or take mass without deforming. The caliber of bullet wasn't big enough to deform the wood by cracking/splinting the wood. The 22. cal. bullet just compressed the wood fibers...wait...just thinking about that makes more sense.... Compressing, is creating heat, heat is thermal energy, taking away energy, giving it the height is goes to. So if you hit it on the side of the wood, it's rotating, rotational is not free...so the thermal energy it takes to compress the wood and the rotational energy it takes to spin the wood is canceling each other out...giving it the same height. Reason we don't see that is cause we don't see thermal imaging...i bet if they did it with thermal camera, the block of wood shot in the middle will be warmer then the one that is rotating, Because the thermal is missing or is replaced by rotational energy in the wood shot on the side.

Maybe?

The wood is receiving all the energy the bullet is creating, but the wood is displaying two different types of energy. One (thermal) is not visible to the human eye. The other is rotational, which we clearly see.

I hope next week they do have a thermal camera.
Click to expand...

I suspect you're on to something with this as well. I think someone else here mentioned that the other thing we can't see is how far the bullet travels into the block. My guess is that it travels further into the block when fired on-center than it does on edge. The difference in the energy required to compress/heat the wood is probably what ends up manifesting as rotational energy.

Conservation of energy is hard to evaluate in real life because of exactly what you just said - you can't just account for potential and kinetic energy, you also need to account for thermal, acoustic, etc. (i.e. the things we're usually told to neglect in freshman physics). I think the conservation of momentum argument is easier to make because there are fewer unknowns.
 
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