- #1
stvsxm
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hi, my high school physics is letting me down here and I just have to get an explanation...
when you talk to gun guys, they say that the maximum velocity that a bullet reaches is the muzzle velocity ... i.e. the absolute velocity of the bullet at the instant that it clears the barrel. their assertion is that , once the gases stop pushing the bullet, that everything after that is " slowing down.
I understand the logic and science of their position but I can't get it to make sense to me. I certainly remember f=ma ... a given force imparted to a given mass results in a given acceleration... fine. then any unbalanced force acts to offset that acceleration. fair enough... so the bullet is immediately subjected to a drag force as a function of air versus its instantaneous velocity and gravity pulling it down...
I did that calculation a hundred times in school... " someone throws a rock of x mass with a force of y lbs off a cliff z feet high in a vacuum . how far does it travel before it hits the ground ? " that was all linear... time to ground etc... but in the real world it just seems , just like the guy throwing the rock, that the bullet accelerates for some period of time AFTER it leaves the barrel before it reaches an equilibrium with the drag and starts slowing down... i.e. max v occurs not at the muzzle but somewhere down range.
just like a pitcher throwing a 100 mph fast ball... the pitchers arm isn't moving at 100 mph when the ball leaves his hand ( is it ? ) so the ball accelerates to max v and then slows down... the velocity is a curve... of distance vs time rather than a straight line ... starting at max and ending at zero... so... somebody please remind me what the truth is , please...
when you talk to gun guys, they say that the maximum velocity that a bullet reaches is the muzzle velocity ... i.e. the absolute velocity of the bullet at the instant that it clears the barrel. their assertion is that , once the gases stop pushing the bullet, that everything after that is " slowing down.
I understand the logic and science of their position but I can't get it to make sense to me. I certainly remember f=ma ... a given force imparted to a given mass results in a given acceleration... fine. then any unbalanced force acts to offset that acceleration. fair enough... so the bullet is immediately subjected to a drag force as a function of air versus its instantaneous velocity and gravity pulling it down...
I did that calculation a hundred times in school... " someone throws a rock of x mass with a force of y lbs off a cliff z feet high in a vacuum . how far does it travel before it hits the ground ? " that was all linear... time to ground etc... but in the real world it just seems , just like the guy throwing the rock, that the bullet accelerates for some period of time AFTER it leaves the barrel before it reaches an equilibrium with the drag and starts slowing down... i.e. max v occurs not at the muzzle but somewhere down range.
just like a pitcher throwing a 100 mph fast ball... the pitchers arm isn't moving at 100 mph when the ball leaves his hand ( is it ? ) so the ball accelerates to max v and then slows down... the velocity is a curve... of distance vs time rather than a straight line ... starting at max and ending at zero... so... somebody please remind me what the truth is , please...
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