(TFT) Power

[Mark Tapley <mtapley@swri.edu>]

At 15:23 -0400 3/27/10, Jay wrote:
> Okay, how about this?
> "let's imagine that a road crew member is shoveling dirt. ... our 
> crew member deposits each load of dirt onto a heap about 4
> feet away (about one hex) from where he is digging. The 4 feet is the
> distance.... tada! -- we have power."
> 55 ft-lbs per second is 10 ST and 1 ST is 1/100th of 1hp.
> 1 horsepower = 745.699872 watts
> 1pt ST is around 7.5 watts

With one caveat, I agree. If the 4 feet is vertical distance - i.e. 
the dirt is being thrown up into a truck-bed 4 feet above where it's 
being dug out of - then the calculation is correct. Moving something 
perpendicular to the force being applied - like rolling a loaded 
railroad car on a level roadbed - doesn't count as "work" even though 
it's not trivial to do. The math for power is "force times (distance 
in the direction of the applied force) per unit time" even though 
it's usually abbreviated as "force times distance per time".
--
						- Mark     210-379-4635
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