# Bullets and truth

Good afternoon -please bear with me -I had to skip physics as a subject -so my knowlege is good in some places, non-existant in others.
There was an interesting post in the archives about the momentum of a bullet -that if two bullets impact with the same energy, the one with more momentum will "kick" more?
Momentum is virtually never mentioned in the gun press, but Energy (KE) is alot -but what does it actually mean? If I shoot something the momentum is what moves the object back -what difference would different levels of energy have? If two bullets have the same momentum, the lighter one will be faster, so have greater KE -what practical effect does that produce?
Related question -a hollowpoint bullet will mushroom when it strikes a liquid/semi-liquid due to a hydralic effect if the bullet is moving fast enough -is this governed by KE or momentum -is the hollowpoint more likely to open if I make the bullet heavier or make it lighter and faster?
phil

## Answers and Replies

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Arcon
Originally posted by phil
Good afternoon -please bear with me -I had to skip physics as a subject -so my knowlege is good in some places, non-existant in others.
There was an interesting post in the archives about the momentum of a bullet -that if two bullets impact with the same energy, the one with more momentum will "kick" more?
Momentum is virtually never mentioned in the gun press, but Energy (KE) is alot -but what does it actually mean?
The kick is related to changes in momentum. However you can't be too careful when considering such statements.

Kick is a force. Force is change in momentum per unit time. The same change in momentum will give a different forces when the time during which the change occurs differs.

The rest of your questions concern damage and that's pretty complicated. Basically, all other things equal, more kinetic energy - more damage. But not all things are usually equal

Thanks for the reply
"more energy, more damage"
Main damaging mechanisms of a bullet are the depth and width of the wound channel (there is energy being lost to the stretch cavity -but that produces little damage with handgun rounds) -how does more KE contribute to these? Does more KE mean deeper penetration?
Any ideas on what the forces that mushroom the bullet are?
phil