Thread: Discussion Efficiency of a ducted fan
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Old Feb 01, 2008, 12:44 PM
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Originally Posted by Texas Buzzard
POWER EQUALS FORCE x DISTANCE/TIME OR THE RATE OF DOING WORK. 1.0 HORSE POWER = 550 FOOT POUND OF WORK DONE /SEC. So if you push a trunk across the floor with a force of 550 pounds and move it 1.0 foot in 1.0 sec then you exhibilted 1.0 H.P. In metric 1.0 Joule of Work done per second = 1.0 Watt. So think that WATT IS EQUAVALENT TO H.P. or just Power.
Work is Ws (WattSecond) = Power times duration.
And 1 H.P. is ~735W.

And by the way. Use International SI units , not imperial units.
The benefit is that you never need to scale units in between and the units will exactly resolve into the unit you need for the result.
Link 1 (sorry, in german, but the tables for derived SI units is missing in the english wikipedia)

This is an incredible help to find out if your thoughts got scewed.
If the result is not showng the righ units you screwed up.

So work [J] = m^2 * kg * s^(-2) = N * m

aka work spend to move something with one Newton force for one meter.

Power [W] = m^2 ∙ kg ∙ s^(-3)

aka work_done divided by time_spend (ask you boss what he considers your work power)

thrust: [N] = m∙kg∙s^(-2)
e-flux: m/s = m ∙ s^(-1)

thrust * e-flux = m∙kg∙s^(-2) * m/s = m^2 * kg * s^(-3) = [W]att

QED (jrb told it already)

Get your thrust by converting the mass units on your scale into Newton

force = kg * g ("g" is earths gravity ~9,81 m∙s^(-2) ) and you get [N]ewton.
1kg = 9,81N

regards Peter

Thats the reason I will never understand americans sticking to imperial units.
It's a mess in physics classes
Not even NASA is able to solve this in imperial units.
May be that why a German was needed to get an American on the moon

My physics teacher in highschool would have thrown me in detention for so many "mistakes"
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Last edited by vampire67; Feb 01, 2008 at 12:54 PM.
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