RE: [DMCForum] Re: You're both wrong! Muahahahahahahahaha!!!!!!!!!!!!!!!
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RE: [DMCForum] Re: You're both wrong! Muahahahahahahahaha!!!!!!!!!!!!!!!!!!!!!!!!!!



James Watt: 1736-1819. R.I.P. we hope.

Find me the equation that Watt wrote down in his notebook where he states
that work = torque and I'll eat this email.

Watt didn't watch a horse for an hour. Actually, he took somebody's word
that a horse could turn a wheel 2.5 times a minute. So yes, time = 2.5rpm.

But how accurate was this guy? He used 3 for pi. LOL

Whilst drinking my drink tonight, I decided that we suffer from lack of
knowledge here and chose to look things up which didn't come from automotive
(hence biased) sources. This meant a whole lot of papers and biographies of
James Watt and a glance at the Department of Energy website, as well as a
look at standards difference between the US and the UK.

Here's what I've found: ... My liquor cabinet needs re-stocking.

Ah. Wait.

But more to the point:

Power = Work / Time

Work = Force * Distance.

Therefore Power = (Force * Distance) / Time.

According to Webster, "torque" is defined as "a measure of effectiveness of
such a force that consists of the product of the force and the perpendicular
distance from the line of action of the force to the axis of rotation." And
"horsepower" is defined as "a unit of power equal in the U.S. to 746 watts
and nearly equivalent to the English gravitational unit of the same name
that equals 550 foot-pounds of work per second."

But wait. An automotive source on the Internet defines "torque" as "the
force at any one point on the edge of a circle in the exact direction of the
rotation multiplied by the radius."

I choose to go with Webster. Why? Hard copy, not written by an automotive
guy trying to prove anything.

Now, wait. If one horsepower is 746 watts, and in Britain "horsepower" is a
gravitational unit ... WTF?

Well, it's a good thing we're not discussing electricity.

James Watt saw an inefficient steam engine and decided to improve upon it.
The term "horsepower" was used back then for the same thing it's used now:
marketing. LOL

According to one chemistry book discussing Watt's steam engines, "Watt is
also responsible for a useful advance in the use of energy units, since for
commercial reasons it was desirable to compare the power of one of his
engines to that of its most direct competition - the horse. At that time
workhorses were usually made to walk around a circular track while harnessed
to one end of a lever attached to a central pivot or capstan. The rotating
shaft of the capstan worked the pumps or other machinery through gears or
other forms of linkage. Watt estimated the pull of the average horse at 180
pounds, and the length of a typical capstan lever as twelve feet. The track
at the end of the lever around which the horse plodded was therefore 2(pi) x
12 = 75.4 feet long. If the average horse completes 144 circuits per hour
the end of the lever travels about 181 feet per minute. The force multiplied
by the velocity is 32,572 foot-pounds/minute, which Watt rounded up to
33,000 foot-pounds/minute, or 550 foot-pounds/second. This new unit was
called a horsepower, as it is still known today. It is likely that over a
workday (then 12 hours) few if any horses could sustain a full
one-horsepower output."

Note that this article is wrong. Watt didn't estimate this. He took another
guy's word - a guy who had horses.

Interesting that we're still using a unit derived from 18th-century math
based on rough estimates and a value of 3 for pi. But there I go off on a
tangent again. LOL

So if one horsepower is 550 foot-pounds a second, based on a value of pi = 3
...

Now, wait. Do we define torque as foot-pounds or as Newton-meters? Which
side of the pond are we on?

Says one scientist, power = torque * rpm. This is closer to what Martin said
when he said "Power is a product of torque and speed." Watt's speed was
2.5rpm, right? What was his power?

I need to know what a radian is to get this next thing to make any sense. I
assume you guys know what a radian is, so I'll post it.

>From the U S D o E website, I find this answer to a kid's question about
torque vs. horsepower: "One horsepower is an estimate of the power a
standard workhorse can exert: 550 ft.lbs/sec.  Before applying any formula,
we must first identify the units of torque.  Torque may be listed as
foot-pounds or as Newton-meters. I will assume your automobile
specifications use foot-pounds.

The power exerted by a rotating object is the torque it exerts multiplied by
the speed at which it rotates. In standard English units, this would be
foot-pounds multiplied by radians/second. It is a special property of
radians that allows this product to be foot-pounds/second: a radian is a
distance around an arc divided by the length of the radius (feet per foot).

We start with 1 horsepower.  We want to get to (foot-pounds)x(rpm).
         1 hp    = 550 ft-lbs/sec        = 550 (ft-lbs)x(rad/sec)
1 rad/sec = 60 rad/min
                                         = 33,000 (ft-lbs)x(rad/min)
1 revolution=2(pi)radians

1 rpm = 2(pi) rad/min
         1 hp    = 5252 (ft-lbs)(rpm)

As for source of rpms, that varies from moment to moment. The number of rpms
will probably be greatest in the lowest gears. When rpms get too great, a
vehicle is usually shifted to a higher gear and a lower rpm for the motor.
The torque tends to be greater in lower gears, when the car is trying to
speed up. Once at cruising speed, all the engine needs to do is
keep the car moving.

Look at the greatest rpm listed on the scale of your tachometer. Use this as
a reasonable maximum. Multiply this by your engine's greatest torque. This
is an estimate of your vehicle's maximum horsepower. Actual value can vary
with speed, with how well oiled the car is, even with humidity."

Now this is all too complicated for me, at least at this hour in this state
in this house on this morning ... You lot can figure it out since you're
smart. I'm just quoting interesting stuff.

>From a website on pumps and BHP calculation: "Just as an artist would begin
a painting by establishing perspective, James Watt began by defining terms
and establishing standards. He defined "Energy" as the capacity to perform
work. "Work" was defined as a force exerted or multiplied over a distance.
And "Power" was work performed within a certain time frame. Energy, power,
and work are terms that many times are used and mixed indiscriminately, but
actually they have precise definitions. An example would be the following: I
have enough Energy in my bicep muscle to pick up a 100-pound weight. If I
were to lift 5 pounds 20 feet, I?ve done 100 foot-pounds of work. Likewise,
if I lift ten pounds 10 feet, or 25 pounds 4 feet, or 100 pounds 1 foot,
then I?ve done 100 foot-pounds of work. If I perform this work within a
second, or within a minute, then this is Power."

What the hell is THIS guy talking about?

>From sizes.com: "The unit of power in the British engineering system, = 550
foot-pounds of work per second = 33,000 foot-pounds per minute,
approximately 745.6999 watts. Abbr. hp. and abbr. B.H.P.

Having invented a practical steam engine that turned a shaft, James Watt
needed a way of rating the power of engines so that customers would know
what size to buy. (The earlier reciprocating steam engines were only used to
drive pumps, and their output was satisfactorily described in millions,
which was the number of millions of pounds of water the engine could lift 1
foot through the burning of 120 pounds of coal?a unit of "duty," i.e.,
energy efficiency.) The most natural way of rating the new engines was to
compare them to the horse, since most potential customers were currently
getting their shaft power from horses, and certainly knew how many horses
were needed to do the job. Smeaton and others had already used such a
comparison.

The horsepower was first defined in print in the Edinburgh Review (January
1809), in an article that suggests that the value of the unit was set
through experiments Watt conducted with dray horses. In James Watt and the
Steam Engine (Oxford, 1927), H. W. Dickinson and Rhys Jenkins point out that
this is probably not so. Among Watt's surviving papers are his "Blotting and
Calculation Book 1782 & 1783." In an entry made in August 1782 he calculates
how large an engine would be needed to power a paper mill currently powered
by 12 horses.

"Mr. Wriggley, [the owner's] millwright, says a mill-horse walks in 24 feet
diar and makes 2½ turns per minute....say at the rate of 180lb p. horse."

The 180 pounds is an estimate of the force exerted by the horse. From these
figures, using a value of pi = 3, Watt calculated the power of 1 horse at 24
× 3 × 2.5 × 180 = 32,400 foot-pounds per minute.

So the figures on which the definition relied appear to have come not from
experiment but from Mr. Wriggley and perhaps other millwrights, men whose
profession was designing and building factories. The job required a very
good idea of the power output of horses; without it the millwright's
factories would not work and he would not obtain new commissions.

Watt used the same value later in the notebook, but under September 1783,
the value is changed to 33,000. A number of considerations may have led to
the new value. Using the same figures as in August but with two more decimal
places for pi would have given 33,912 instead of 32,400, but Watt would want
a number easily used in calculations. A multiple of 60 (minutes) would be
especially attractive. Further, by choosing a value that was larger than a
real horse's actual output, Watt was following the old engineering principle
that it is better to be too big than to fail. Steam power was new, potential
purchasers were skeptical and installations that failed were more likely to
be noticed than those that performed as planned. All of which suggests that
the choice of the value of the horsepower was essentially a
back-of-the-envelope estimation.

In Watt and Boulton's factory the word "horse," not "horsepower" was used,
e.g., a "10-horse engine."

Modern measurements show that the average horse can put out about 0.6
horsepower through an 8-hour workday. This is consistent with Watt's desire
to rate his engines conservatively."

I think it's safe to say that Watt was not using "work = torque". As far as
RPM, he did say that "a mill-horse walks in 24 feet diar and makes 2½ turns
per minute....say at the rate of 180lb p. horse", so it could be argued that
he was counting revolutions per minute: 2.5rpm.

Okay, I'm lost. Which equation were we talking about? I forgot. Plus it's
time for the end of my nightcap. Nighty night all. I look forward to reading
inspirational messages when I get to work tomorrow. I wonder if I'll care by
then. LOL

You guys are the smart ones. Take this info and come up with something
useful. I'm too tired to study any more. Bleh.


Bill wrote:
> Bad news big boy:
>
> In Watts equation:
> "Work" is torque
> "Time" is RPM's (not time on a clock)
>
> http://www.houseofthud.com/cartech/torqueversushorsepower.htm
>
> Remember: Watt was counting the number of revolutions a hourse could
> make on a treadmill within an hour, which he then calculated down to
> revolutions per minute (RPM).
>
> The mere number of minutes an engine is running has no more bearing on
> HP than Martin's bizarre "speed" comments (MPH?!)
>
> Bill Robertson
> #5939


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