On Sun, Mar 4, 2012 at 2:49 PM, Phil <philgoetz@gmail.com> wrote:
Half (I think?) of the energy in a
bullet goes into the gun, and a gun is a lot less massive than a BSC.
Well, no.
In the limiting case of a rifle fired into the air, with it's butt resting on the ground,
the rifle's motion is effectively zero, so all of the energy goes into the bullet.
Energy is mass times velocity squared, and if velocity is zero, so is energy.
In the case of a 2.25 kg pound rifle firing a 9.7 gram bullet, less than half a
percent of the energy goes into the rifle, and more than 99.5% goes into the
bullet.
Anything that can knock a BSC weighing several hundred
pounds a few inches... well, do the math if you're curious, but I
doubt that a bullet could do that.
Of course I'm curious, and the math is simple.
The BSC mass is 272 kg.
You say it jumped a few inches -- lets call it 10 cm.
Let's say it came to rest in a single second, so the speed is 0.1 meters per second.
The energy is then 2.72 joules.
This is not surprisingly a fairly small amount. I can move a 600 pound box a few
inches without getting winded. Moving my own 200 pounds a few inches three
times is not a lot of effort either.
Calculating the energy in the centrifuge is also fairly easy, but to make it even
easier, let's just ask how long it takes to spin up, and what size motor is used
to power the air compressor. A 200 watt (1/4 horsepower) motor, running for 30
seconds is 6,000 joules of energy. The centrifuge system is probably 10% efficient
at best at converting that electricity into rotary motion, as most of the energy goes
out as wasted high speed air. Call it 600 joules. An AAA battery has 1,000 joules
of energy. A candy bar has a million.
The muzzle energy of a .38 special is 420 joules.
A .44 magnum gets you 1400 joules.
Let's look at a 5 inch diameter rotor (I'm guessing at the diameter) spinning at 53k rpm,
or 883 revolutions per second. The speed at the circumference (pi * 5 inches, or 40 cm)
is 353 meters per second. That's in the same ballpark as a .22 rifle bullet. But that is the
speed of the very outside edge of the rotor. An inch in from the edge, you only get 200
meters per second.
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