Okay so I know that KE is .5mv^2 and momentum is mv and that KE is scalar while momentum is vector. My question is how/why they are different.
If something with high momentum hits me how is that different from being hit by something with high KE? Or alternately is there a rule of thumb for when one or the other should be used?
I've spent the last several days searching the internet and the only helpful thing I found was "Kinetic energy is how much energy a moving body can carry. Momentum determines how that energy is delivered." but even that isn't particularly clear.
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The difference is in conservation of energy. Linear momentum is conserved even after collisions and separations...Kinetic energy is not if the collision are inelastic.
In an inelastic collision (the only kind you can see in everyday life) kinetic energy will turn into sound, heat and a bunch of other stuff while momentum in the whole system remains the same.
This is why when someone is shot a lot of damage happens but you don't go flying. The bullet has a lot of KE (it's very fast) which is lost ripping up your body. The bullet has low momentum (about the same as a baseball) and that isn't enough to move your body very far.
Or at least that's the impression I get.
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Apr 5th, 2010 12:43 AM
