[DMCForum] Re: Salt or Pepper with Farrar's eMail?
From: "content22207" <brobertson@xxxxxxxxxxxx>
Date: Wed, 14 Jan 2004 05:49:12 -0000
OK Farrar, let's use your "Work = Force x Distance" standard:
Watt may have never used the word "torque" in his journals,
substituting instead the word "force", but if you look up the
definition of "torque" in Barnhart's dictionery (better than
Webster's) it reads: "1) *FORCE* causing rotation 2) the moment of a
system of *FORCES* causing rotation". (Emphasis is mine because THEY
MEAN THE SAME THING!).
Even your Webster's definition uses the word "force".
"Distance" is of course circular rotation, not a linear direction,
which is what crankshafts do.
Do you want salt or pepper with that eMail...
Your argument that torque doesn't exist because Watt never used the
word is like saying this whole issue hasn't become ultimately "outre'"
because no one on the Forum has ever used that word (it means
"ridiculous"). Torque exists even if Watt merely gestured and made
unintelligible noises.
BTW: approximately 1/3 into your post you state:
>Says one scientist, power = torque * rpm. This is closer to what
>Martin said when he said "Power is a product of torque and speed."
Not to be technical, but way back in Message #10025 I reiterated the
classic calculation of HP = Torque x RPM / 5252. Don't worry about
acknowledgement -- I've come to NOT expect it. I do hasten to point
out that nowhere in your scientist's formula is Martin's bizarre
"speed" comment to be found, yet *MY* RPM's are there in glaring black
& white. Don't worry about acknowledgement -- I've come to NOT expect it.
Forget the shaking head emoticon, I need a vomiting one.
Bill Robertson
#5939
>--- In DMCForum@xxxxxxxxxxxxxxx, "Farrar Hudkins" <fhudkins@xxxx> wrote:
> 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