(TFT) Energy, units, cautionary notes.

[Mark Tapley <mtapley@swri.edu>]

At 3:07 -0400 3/26/10, Jay wrote:
> Dynamite ~20,000fps or ~3,636 ST

	Jay, I have trouble with your choice of units here. 
Converting a "ST" to a speed (feet per second) just doesn't seem 
consistent. Put another way, the speed has to be connected with a 
mass to mean anything in terms of either energy or momentum. A single 
atom at 20,000 fps is negligible, whereas a locomotive at that speed 
would be almost thermonuclear.

	I would be happier (not completely happy) connecting "ST" to 
either momentum or (kinetic) energy, since to at least some 
approximation, strength allows you to pack momentum and energy into a 
tool or projectile (during a throw, or a swing).

	I would be happiest connecting "ST" to *power* (Watts), or spelled out,

Watt	= Joule/second
	= Newton meter/second
	= (kg meter/second^2) meter / second
	= kg meter^2 / second^3

At 3:07 -0400 3/26/10, TFT Digest wrote:
> "It is estimated that the human body reaches 99% of its low-level terminal
> velocity after falling 573m 1880ft
> ... at normal
> atmospheric pressure and in a random posture."

	...but of course, by the time they have fallen 1880 ft, 
atmospheric pressure has changed, increasing the density and reducing 
terminal velocity, so it's more complicated than just an asymptote.

Drag = 1/2 (density) (velocity)^2 (area) (Coefficient of Drag)

At 3:07 -0400 3/26/10, TFT Digest wrote:
> So it's all about the energy huh?
> Ooooooookay.

	In a lot of ways it is.

	On very short time scales, *momentum* (mass times velocity) 
is also important, but friction erases that pretty fast for most 
medieval applications. Well, meteorology is an exception. Coriolis 
force, based on momentum of large masses of air, causes hurricanes, 
tornadoes, etc., which are really ways that nature manages to 
*concentrate* energy. Lightning is one other exception; there 
triboelectric effects work to concentrate sunlight (pretty diffuse 
power) into a very concentrated (both in time and in space) form of 
energy - so the *power* is amplified considerably.

	But for most purposes, tracking available and expended energy 
is a good way to measure civilization.

At 3:07 -0400 3/26/10, TFT Digest wrote:
> This brings us back to that 0.1 hp per person of work.
> Aparently, Egyptian priests told Herodotus that up to 100,000 men worked on
> the Great Pyramid at once.
> At about 0.5g protien per kg of "ideal body weight" per man per day in food
> (just above starvation), this
>
> equates to about 550 footpounds of work over the course of a workday
> (10hrs?).

	1 horsepower = 745.7 Watts = 550 foot-pounds per *second*, 
not per day. If a worker really could sustain 0.1 hp over an 8-hour 
workday, that would be 1584000 foot-pounds. It's probably 
unreasonable to think of a worker actually moving that much (?), but 
certainly 5 pounds 11 feet in one second is quite reasonable.


At 3:07 -0400 3/26/10, TFT Digest wrote:
>  This simple and specific situation not only proves the ability
> to percieve 1 image within 1/220
> of a second, but the ability to interpret higher FPS."

	I disagree. I think it proves that the optic system 
(detectors, nerves, etc.) can be affected within 1/220 second such 
that the after-image is enough for the brain to grasp, process, and 
recognize the shape that caused the after-image. But realistically, 
if frames were being sent one after another at 220 frames per second, 
could the pilot later say, "yes, numbers 7 and 33 were MiG-23's"? I 
strongly doubt it. A single frame will produce an after-image lasting 
seconds, which is plenty of time. But the Ted Williams experiment 
pretty much demonstrates that 1/220 second is not enough time for the 
brain to do much of any processing, IMHO.

	I think the 0.215 seconds from the web site is a lot closer 
to a reasonable time for a "dumb" reaction (flinch) and I think 
somewhat longer for a "complex" reaction (Door #1, Door #2, Door #3) 
would be appropriate.


At 3:07 -0400 3/26/10, TFT Digest wrote:
> Biomass energy

	But note, a lot (most?) of the mass that contributed to the 
energy release was oxygen in the atmosphere, floating around the 
biomass before it burned.

At 3:07 -0400 3/26/10, TFT Digest wrote:
> US measure: 106 pounds for 60 inches in height
> + 6 pounds for each additional inch over 60 inches

	Ew. I have to lose *15 lbs?* Ew. ;-)
--
						- Mark     210-379-4635
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Large Asteroids headed toward planets
inhabited by beings that don't have
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				Think of it as Evolution in Fast-Forward.
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