OK Mr. Wizard, explain escape velocity to me.
- Thread starter kcollins4
- Start date
is it really true that a bullet follows a parabola, and that it will hit with the same force it left the barrel? It doesn't seem perfectly logical, I guess I have never thought of it.
I know that if you shoot a gun horizontally and drop a bullet at the same instant it's fired, from the same height, the bullets will hit the ground at the same time, but that will change of course if you shoot at any upwards angle, since you are going against gravity during the rise. You'd have to drop the bullet from the same height as the bullet's peak, and then they'd hit the ground at the same time.
I guess what I'm missing is how do you calculate the acceleration and the effect of the deceleration on the bullet as it's still gaining speed, gravities pull is always the same of course, but it seems that the bullet would have more velocity going out of the barrel than it would at the same height coming back down, because gravity can't accelerate the bullet downwards as fast as the powder sends it upwards, follow me?
Maybe I'm just confusing myself, I've been known to do that. And I have already been quite wrong once on this thread already, let's go for 2! Crexrun
Simplified: I think the bullet will travel faster during the first part of it's curve on the parabola, and gravity can't pull it as fast as the powder propelled it, so the equal half on the opposite side of the curve will be slower on average, especially at it's mirrored point, on the backside of the curve.
It doesn't seem that say, 3,200 fps at 6 feet off the ground here equals 3,200 fps 1/2 mile away, at the bullets landing point, 6 feet off the ground. But maybe that wasn't the point anyway, and I'm still missing something.
I know that if you shoot a gun horizontally and drop a bullet at the same instant it's fired, from the same height, the bullets will hit the ground at the same time, but that will change of course if you shoot at any upwards angle, since you are going against gravity during the rise. You'd have to drop the bullet from the same height as the bullet's peak, and then they'd hit the ground at the same time.
I guess what I'm missing is how do you calculate the acceleration and the effect of the deceleration on the bullet as it's still gaining speed, gravities pull is always the same of course, but it seems that the bullet would have more velocity going out of the barrel than it would at the same height coming back down, because gravity can't accelerate the bullet downwards as fast as the powder sends it upwards, follow me?
Maybe I'm just confusing myself, I've been known to do that. And I have already been quite wrong once on this thread already, let's go for 2! Crexrun
Simplified: I think the bullet will travel faster during the first part of it's curve on the parabola, and gravity can't pull it as fast as the powder propelled it, so the equal half on the opposite side of the curve will be slower on average, especially at it's mirrored point, on the backside of the curve.
It doesn't seem that say, 3,200 fps at 6 feet off the ground here equals 3,200 fps 1/2 mile away, at the bullets landing point, 6 feet off the ground. But maybe that wasn't the point anyway, and I'm still missing something.
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In a vacuum it will. Not on the Earth's surface.
When the trigger is pulled, chemical energy in the bullet is transformed to kinetic energy, propelling the slug out of the gun. As the bullet rises, KE is transformed to potential energy as gravity slows it down. PE reaches a maximum at the apogee where the slug momentarily stops and reverses direction, then PE is transformed back to KE as the slug picks up speed falling to the ground. If there were no atmosphere, then the law of the conservation of energy says the bullet must hit the ground with the same force it left the muzzle with. But here on Terra, the atmosphere prevents that, since some of the energy will be transformed to heat both on the trip up, and the trip down.
Would a slug retain enough energy to kill someone when it came back down? Depends on the slug and how well it can slip through the atmosphere. An AK-47 round is a heavy, pointy little bastard, and could probably do so easily. A pistol round from something like a 9mm might not, but I'm not volunteering as guinea pig to see.
The bullet doesnt accelerate anymore once it leaves the barrel...the fastest point is when the explosion takes behind it...that is the only fwd force applied (a push)..at all times, the bullet is subject to gravity. if the barrel is not pointed upwards, but straight, the bullet will follow half a parabola. the highest point being the spot where fired.
Air resistance notwithstanding, if the bullet didnt land with the same velocity, it wouldnt follow a parabola, as the vertical component of the forces would be greater on the way down than on the way up. the available kinetic energy on the way up must equal the kinetic energy on the way down. Air drag is the same for both halves of the parabols.... In space, there would be no parabola, as gravity would not influence the bullet. (although there is gravity everywhere in the universe, but with negligible effects)....If this wouldnt be the case, once a cannon shell reached the apex, it would fall faster...and that is not the case....
Air resistance notwithstanding, if the bullet didnt land with the same velocity, it wouldnt follow a parabola, as the vertical component of the forces would be greater on the way down than on the way up. the available kinetic energy on the way up must equal the kinetic energy on the way down. Air drag is the same for both halves of the parabols.... In space, there would be no parabola, as gravity would not influence the bullet. (although there is gravity everywhere in the universe, but with negligible effects)....If this wouldnt be the case, once a cannon shell reached the apex, it would fall faster...and that is not the case....
I hate to say it, but terminal velocity affects that straight up and down bullet.
But it's still bad news. That's why New Years eve in some places is so dangerous, even when the twit is firing straight (how straight???) up. (that one degree error adds up quick)
There is something called a ballistic coefficient that basically is a measure of the bullets ability to pass throgh the air. Long distance competitive shooters use software that figures in barometric pressure, ambient temperature and relative humidity to name a few... to get the drop characteristics for that shot.
FWIW more energy is locked up in the spin of the bullet than in the velocity, sometimes when the velocity is boosted too high for a barrels' twist the round will disintegrate in midair... the jacketing on a bullet can actually hold it together. That is the foundation for "varmint" shooting.
But it's still bad news. That's why New Years eve in some places is so dangerous, even when the twit is firing straight (how straight???) up. (that one degree error adds up quick)
There is something called a ballistic coefficient that basically is a measure of the bullets ability to pass throgh the air. Long distance competitive shooters use software that figures in barometric pressure, ambient temperature and relative humidity to name a few... to get the drop characteristics for that shot.
FWIW more energy is locked up in the spin of the bullet than in the velocity, sometimes when the velocity is boosted too high for a barrels' twist the round will disintegrate in midair... the jacketing on a bullet can actually hold it together. That is the foundation for "varmint" shooting.