Date: 13 Nov 1993 01:11:40 GMT
From: Jordin Kare <jtk@s1.gov>
Subject: English vs. metric units question
Newsgroups: sci.space,sci.astro,sci.physics

In article <2c13of$skq@mailer.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr) writes:

>This has been chewed over a lot, but I thought it should be added that 
>we use metric sizes for automobile engines in the US, and metric 
>countries still measure their power in Horsepower.  These sorts of 
>units are kept around because people know what they mean, more or 
>less.  A car with its power in Watts?  No way. 


Unless it's an electric car, of course :-)

Incidentally, a horse is capable of generating about 5 horsepower
(as long as you don't ask it to do so for very long)

Actually, it's trivial to convert horsepower to watts; it's got one
of the best mnemonics I know:

In 1492
Columbus sailed the Ocean Blue
Divide the sonofagun by 2
For the number of watts in a horsepower (=746)

	Jordin Kare

Newsgroups: alt.energy.renewable,sci.energy,rec.crafts.metalworking,sci.engr,
	sci.energy.hydrogen,sci.environment
From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: M.Earth News: 6.2 kWe from 1.5 HP?
Date: Thu, 08 Aug 1996 15:49:02 GMT

jmc@Steam.stanford.edu (John McCarthy) wrote:

>Can you give a current figure on pounds of coal per horse-power hour?
>I want it to compare with the 1800 figure of 100 lbs of coal per
>horsepower hour and the 1900 figure of one lb of coal per horsepower
>hour.

The BP Statistical Review of World Energy uses 1.5 tonnes of coal
( as produced ), or 1.0 tonne of oil,  as producing 4,000 kWh of electricity
in a modern power station.  1 Horsepower = 0.7457 kW

You also might be interested in the very interesting letter to Nature on
the horsepower from a horse. ( Nature v.364 p195 15 July 1993 ), they
calculated the various types of horsepower from a horse.  In 1925
Collins and Caine measured peak powers of 12-14.9 hp for just a
few seconds.  Youatt in 1826 said a draught horse should pull 10%
of its body weight at a rate of 2.3-3 miles/hr for a 10 hour working day
to maintain health and vigour. Collins and Caine agree, and that figure
is very similar to the 1hp derived by Watt in the 1780s by determining
from millwrights that a horse could walk around a 24ft diameter
mill whell at average of 2.5 times/minute for a day's work. He assumed
the horse exerted a tractive effort of 180 pound force, yielding a power
estimate of 33,929 ft-lbf min. In his blotting and calculation book, this
number was rounded to 33,000, thus producing the more familiar
550 ft-lbf sec definition. He needed the power estimate so he could
sell his rotary steam engines to replace horse gins, as annual payment
was based on number of horses replaced.

[ followups set to sci.energy ]

             Bruce Hamilton

Newsgroups: sci.energy
From: John De Armond
Subject: Re: How many BHP a KW ?
Message-ID: <_-r8x1g@dixie.com>
Date: Tue, 26 Jul 94 02:34:08 GMT

alf@amki.toppoint.de (Alfred Mechsner) writes:

>Hello,

>today I got confused with BHP. As far as I know, this are
>either brake horse power or british horse power.

>So I looked it up and found a conversion factor
>of
>    1 KW = 1.341 HP

>at a tabel for anglo-american units.

>Looking at diesel engines builders catalogs i realized,
>they used a conversion factor of

>   1 KW = 1.36 HP

>which is exact the same conversion like PS (in german Pferdestaerken,
>which is horse powers).

The standard mechanical HP (B stands for "brake", an indication of
mechanical power.) is 33,000 ft-lb/minute or, according to "Engineering
Unit Conversions" by Lindeburg, 745.7 watts.  This book lists the
following other "HP"s:

Boiler HP = 		9809.5 watts  (No, I didn't slip a decimal)
Continental HP = 	736 watts
Electrical HP =		746 watts
Metric HP =		735.5 watts
U.S HP =		745.7 watts
Water HP = 		746.04 watts
Ad Agency HP = 		Whatever they choose :-)

Ain't standards grand?

John