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Everyone's heard the urban legend that a penny dropped from the top of
a skyscraper becomes a lethal projectile. Fortunately, this isn't the
case, as air resistance prevents falling pennies from accelerating once
they've been falling for 40 feet or so. The falling coins can't descend
fast enough
to hurt a person on the ground below.
BBs, however, aren't subject to the amount of air resistance that flat
pennies are. During times of war, planes filled with as many BBs as
their cargo holds can carry could fly over enemy territory, or army
camps, and unload their cargo. These dense metal BBs would
accelerate to bullet speeds and rain down upon the ground, causing
severe damage.
It's Rainin' Blood
http://www.youtube....watch?v=CUDWLp1yIWw
[jaksplat, Aug 26 2009]
Bryan Ferry's version
http://www.youtube....watch?v=d77yJyDBcTA
[coprocephalous, Aug 27 2009]
Human-rain
Human_20Precipitati...Defence_20Programme
Terrifying prospect... [theleopard, Aug 28 2009]
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Annotation:
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I'm pretty sure a BB has a terminal velocity below 1600 fps. |
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You really do have an evil streak, don't you? |
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lookup the word "flechette". Basically a steel dart, used in many interesting ways. Think beehive rounds for tank cannon. |
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In WW1, and I think WW2 as well, bulk volumes of flechette were dropped from aircraft in an antipersonnel capacity. Flechette are many times more effective than bb's for this purpose, and are well baked at that. |
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Anyhoo, terminal velocity is all about drag vs weight. Largely that's a sectional density issue. |
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I will bet a small amount of good beer that a sphere such as a bb has a poorer terminal velocity than a disc such as a coin falling edge-on ie cutting through the air. Also note that on average, terminal velocity increases as you scale up the size of the items being used. An interesting experiment would be to measure the statistical spread of velocities of coins randomly dropped from a given height, versus coins given spin (so as to stay edge-on while falling). I think a spinning coin falling from a great height may still be dangerous. |
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//a sphere such as a bb has a poorer terminal velocity than a disc such as a coin falling edge-on ie cutting through the air// |
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Warning. Assumptions ahoy. I meant to add the text "within reasonalbe limits of thickness-to-diameter dimensions of the coin" - of course. |
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//During times of war, planes filled with as many BBs as their cargo holds can carry //
This is exactly what happened - during WW2 unarmed BOAC-liveried Mosquito fighter-bombers flew from Sweden to the UK with their bomb-bays loaded with ball-bearings, but they were far too precious to drop on the enemy.
Instead, much bigger bombers flew over Schweinfurt, and dropped their explosive bombs on the ball-bearing factory there.
(I have a feeling that just before this happened, the Allies bought the entire Swedish production, to deny the Germans an alternate source - maybe the Allies were worried that the Germans were going to drop ball-bearing-based V weapons on them).
What they all said about flechettes. [-] |
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Make your BB's of sodium, store them in mineral oil, then pump them out. With sodium, terminal velocity doesn't matter. |
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// sodium, .... store them in mineral oil // |
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That sounds familiar .... do you think it would smell nice in the morning ? |
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"Good old Dow Chemical. They're not just for the nice things in life...." |
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"Guaranteed to break the ice at parties" |
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Far more concerning is the prospect of raining men. They're
bigger and will more than likely kill you if you get hit. Let
alone the psychological trauma of seeing hundreds of corpses
exploding around you. |
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However, it's all been dealt with, thankfully, in the [linky]... |
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No, the ones that can fly are Witches, and therefore guilty ...... |
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//air resistance prevents falling pennies from accelerating once they've been falling for 40 feet or so.// |
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I wonder if this holds true for a spinning penny? If its tilt were in line with its acceleration the wind resistance would be greatly reduced. |
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But slipping on the balls afterwards _could_ cause death. |
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