The summer after i graduated highschool, myself and three other somewhat shady characters rented a farm house north of town for the summer. We drank most of that summer, so some of my memories are a bit cloudy. Anyway we would shoot barn swallows out of the air with 22LR ammo just as the swallows would enter there den in the top of the old corn crib, that was on the property. Somehow, one of us missed a shot on one of those barn swallows, and the bullet traveled about 1 mile and planted itself in the neighbors pole barn. So this s what i know. After the ass chewing we got from the neighbor, and the promises the conservation officer gave us about going to jail if we ever pulled that stupid stunt again, i have never shot another single bullet up into the air. I will also say that shooting barn swallows with a 22lr while they hovered was a lot of fun!! However fun it may have been, it wasnt one of my brighter moments in my journey of life. Lee
V
Vibe
Guest
4mesh
It's called angular momentum - and the axis "wants" to remain pointed in the same direction. The Mass Moment of Inertia is less about the log axis and creates a given amount of angular momentum at a given RPM. Change that axis of the bullet away from the axis of rotation and the bullet will start precessing (coning) - trying to wobble like a top slowing down. This does a couple of things. The angular momentum only represents a given amount of energy and as the Mass Moment of Inertia goes up due to the change in axis alignment - the rotational speed will go down. That's a bit over simplified, but it's a start.
It's called angular momentum - and the axis "wants" to remain pointed in the same direction. The Mass Moment of Inertia is less about the log axis and creates a given amount of angular momentum at a given RPM. Change that axis of the bullet away from the axis of rotation and the bullet will start precessing (coning) - trying to wobble like a top slowing down. This does a couple of things. The angular momentum only represents a given amount of energy and as the Mass Moment of Inertia goes up due to the change in axis alignment - the rotational speed will go down. That's a bit over simplified, but it's a start.
4
4Mesh
Guest
Vibe,
I think we're on the same page there, those things can be observed with most any object. But where I think Ray and company are loosing me is that many of the horizontal flight forces which cause the bullet to tumble, are not present when fired upward. So, the thing basically stays point up and then falls straight back down base first. Or, at least that's what I'm taking from what they're saying. So I guess I can buy into parts of it, but then the guy also has situations where the bullet falls tumbling (hits sideways, or that is what I'm reading anyhow). So, nothings real predictable here. For all i know, two of the same bullet may act differently.
Maybe I'll spend the day shooting bullets straight up!
I think we're on the same page there, those things can be observed with most any object. But where I think Ray and company are loosing me is that many of the horizontal flight forces which cause the bullet to tumble, are not present when fired upward. So, the thing basically stays point up and then falls straight back down base first. Or, at least that's what I'm taking from what they're saying. So I guess I can buy into parts of it, but then the guy also has situations where the bullet falls tumbling (hits sideways, or that is what I'm reading anyhow). So, nothings real predictable here. For all i know, two of the same bullet may act differently.
Maybe I'll spend the day shooting bullets straight up!
M
mks
Guest
Yes, good start. Conservation of angular momentum explains why a skater doing a spin speeds up when she draw her arms and legs in close, and slows down when she extends them out.
The bike example has an additional effect related to the change of orientation. Angular momentum is conserved along each of the three axes that define three-dimensional space. Angular momentum for the spinning bicycle wheel exists only around the axis defined by the axle. When you rotate the axle 90 degrees, the force required to rotate it eliminates the angular momentum in the original direction, and converts very little of it to the new direction of the axle.
"hits sideways" doesn't equate to tumbling. Hurl a piece of lathe, it doesn't tumble, it just precesses, predictably.
I submit that a falling bullet rifle achieves an "angle of repose" about 30-60 degrees off vertical depending on it's shape, with a very slow ""helicopter" motion. And that any given bullet will do this predictably. It will land sideways by a certain amount, not just flopping around randomly.
al
M
mks
Guest
Right - none, zero, whatever you want to call it.
M
mks
Guest
In a vacuum, velocity v = v0 - gt, where g = 32.17 ft/s^2 and picking initial velocity v0 =3217 fps, gives time t = 100 s for how long it takes the bullet to top out (v = 0). The elevation is then y = v0t - 1/2 gt^2 = 160850 ft = 30 miles.
In air, the bullet slows down much faster, and the calculation is complicated by the change in air density and the transitions from supersonic to subsonic flow and turbulent to laminar flow as the bullet slows down. An exterior ballistics program would get a more realistic answer, but I don't know of any that take all these factors into account. No doubt our military has done such calculations for trajectory with large altitude and velocity changes. A guess might be, say, half as far?
Cheers,
Keith
S
swmft
Guest
What no one seams to mention is that holding a gun you are unlikely to get a perfect 90 so when it hits earth the round could kill. We get at least one person seriously injured or killed per year from fools that shoot in the air to celebrate.