Lynn,
It does not take HP to move a mass through a distance.  It takes zero HP and
you have done no work if you carry a 100 pound sack of potatoes the length of
a football field.  Carrying that bag up a flight of stairs is another story.
It does take HP to start a mass moving, to accelerate it, to raise it, to
stop it, or even turn it.  And It does take HP to overcome the drag that
airplanes continually develop while flying.

Bob Darrah

Anytime work is being accomplished it can be measured and expressed as horsepower. Moving a weight through a distance (in some period of time) is work. The system being used to accomplish the work makes no difference. Whether or not the force involved is used to lift 33,000 pounds straight up one foot,( a bunch of power) or carry 100 pounds of potatoes 10 miles,(a tiny bit of power)its the same thing. It's easy to see the rule when imagining the horse, the pulley and the big block of concrete being lifted one foot, as in the dictionary. It is less easy to see in the field hand carrying the potatoes. 

If we give him credit for performing work when he picks up the sack, as in 100lbs X 4 feet x .09 minutes, will we dock him when he puts the bag gently back down ten miles down the road, 100lbs - 4 feet X .09 minutes? 

No. He performed work in both cases. He did not perform work in the first case and get it back in the second case. Any mass moved by a force,in any direction over a period of time is work, and the amount of work accomplished can be expressed as horsepower. Even when the force is gravity. Even in space with gravity left out of the picture, when a spacecraft accelerates from 14,000 MPH to 24,000 MPH work has been accomplished, and the amount of work can be expressed in horsepower. 

An interesting topic might be....why are large diesels rated in kilowatts instead of horespower? 

Why do many people operate large aircraft engines with mixtures lean 
of peak power to extend engine life and reduce cylinder head tempertures? 

Which is worse preignition or detonation? 

What is the difference between a hot plug and a cold plug? 

How do I tell if I need two, three, or four blades on my prop. 

Which fuel has more energy, 110LL or 80/86 ?

All good questions but most a bit far afield for the ACRE NL.
Well maybe not the prop question? :-)

Paul Lamar

 
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