Bullets falling back to earth

Particularly in the extreme case of a bullet fired a few feet above the ground horizontally.

On 16 Dec 2003 16:55:52 -0800, jim rozen brought forth from the murky depths:

When my grandfater was 93, the California Highway Patrol followed him home one day from Interstate 5 in L.A. and warned my grandmother to watch him so he would keep that 3-wheeled bicycle of his OFF THE FREEWAY. He decided that the freeway was the shortest route home that day.

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To slide rule accuracy. :-)

BTW, it's "vacuum" that's the key word.

Ted

But that is a poor approximation for a realistic balistic situation.

Ted

An object, for simplicity, falling straight down in still air has two forces acting on it, the force of gravity, m/g, and the force of aerodynamic friction. These will act in opposite directions and will be equal at terminal velocity.

Ignoring this will just confuse you.

Ted

Maybe, Ted, but *acceleration* from gravity is not diminished in any way. At each instant, dt, acceleration is still present. The result is offset by the drag of the air and a sort of equilibrium seems to exist, but acceleration from gravity is constant. Matter of fact you and I are accelerating right now toward the center of the earth - but our movement is arrested by offsetting forces. Nevertheless, at any given instant, dt, we are accelerating.

Bob Sw>

I was singularly underwhelmed by that technique. I noticed they not only applied them hot, but fumbled a rivet into them from the wood side while doing so. This of course means the rivet couldn't be set properly (with the wood for a backup) and the band burnt away the very wood it was supposed to be buttressing.

The right way to band a trunk would be to do what coopers do: drive the bands on after they're made and rivited. All they need is to adze a bit of taper into the trunk to make that easier. AND that would have avoided a lot of toxic smoke.

As for making one in one day ... no doubt in my mind that it can be done. For one thing, the auger was probably driven by horsepower, and the pressure was probably applied by leverage. After all, we use drill presses which act in precisely the same way in principle.

They may be cool, but they are largely fools in some respects ... I saw one of them burn off an eyebrow and most of his hair *and* get flash burns while fooling with gasoline vapors, and he was so lacking in pride as to let that be shown in the episode. Also, they make mistakes in fact. The Cola episode is a case in point. CC is actually an excellent fluid to use on rusted fasteners; I've seen it loosen muffler clamp bolts that were just about solidy corroded on.

Regards, Hoyt McKagen

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Not if you can provide an adequately sized cylinder of vacuum from the rifle up to the zero-velocity point and back down. :-)

Granted -- with air in the equation, it makes a *big* difference.

Enjoy, DoN.

Oh darn! That'll be seriously bad news to parachutists.

Bet ya don't see snowflakes accelerating at that rate.

Roger that. Revolting waste of good muskie bait,

Acceleration is, by definitition, rate of change of velocity with time AKA dv/dt. If me arse is changing velocity at the moment I sure don't notice it.

Gravity is a force proportional to mass which makes it acceleration in terms of math units, but that only becomes dv/dt in a force equation after other forces like restraint ( the stool me arse is perched on) and viscous or aerodynamic drag that impedes the descent of snowflakes, parachutists, and other falling objects is included.

Hatchers Notebook (a monstrous book available from Amazon or the library) has a section on this, including tests. Aerodynamic drag plays a big part. Having said that, I wouldn't stand under falling bullets. Geoff

That's not what Hatcher reported. The bullets came down base first, and still spinning at a great rate.

Gary

Hatcher doesn't mention that (his tests took place ~ 1920), but estimates that a 1000 lb. 12" shell, fired straight up, would reach a terminal velocity between 1300 and 1400 fps, with over 28,000,000 ft. lbs of energy. He estimates that a 718 grain bullet from the .50 Browning would reach nearly 500 fps, with less than 400 ft. lbs. energy.

R, Tom Q.

With regard to the 150 grain, flat base Service bullet, he doesn't actually say point blank that it was always stabilized and always fell base first, but it's very clearly implied.

He reports different results when using a 175 grain, boat-tail bullet (experimental Model of 1919). The time of flight using these bullets was either 1 min. 6 sec. (base first) or 1 min 46 sec. (tumbling) leading him to believe that the bullet's stability was marginal.

R, Tom Q.

Don sez:

"Acceleration is, by definitition, rate of change of velocity with time AKA dv/dt. If me arse is changing velocity at the moment I sure don't notice it."

That's because you aren't (we aren't) finely tuned enough to notice the teensy-tiny interval dv/dt.

Bob Swinney

Yep! Stands to reason the rotational velocity would sustain long after forward velocity.

Yes, it's still rotating, but is there enough spin remaining to stabilize a bullet falling base first? The rifling twist is usually chosen to impart the necessary spin to a limited range of bullet weights within a range of speeds (relatively fast speeds, compared with falling) for a bullet fired point first. It's counter-productive to spin the bullet much faster than is required for normal firing conditions.

Let me go out on a limb and say that sometimes the bullet remains stable and sometimes it doesn't.

R, Tom Q.

Did he also complain to your grandmother that all the other damn fool drivers were going the "wrong way" on that side of the freeway and nearly killed him? (G)

Jeff

-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."