^^^^^^^^^^^^^^^^^^^^^^^^^^   FAST!  8^)

I thought this up recently.  Think of yourself trying to push a large
heavy object.  It's harder to push it slowly than to pick up some
speed and push it.  Wouldn't the same be true of an engine?  I.E.,
once you overcome friction and get some inertia going, your engine
has to work less.  Physics people?  What about it?

--
j...@access.digex.com  | (Cage) 1991 323se     ZCP-710   |     Comus Road
Merry Land (MD) U.S.A. | (Bike) 1986 GSXR750    (sold)   |     ClarksBURG
-------------------------------------------------------------------------
Riding with your feet on the passenger pegs places your body at the perfect
angle for maximum penetration into the frames of most automobiles!  X^(

In article <1992Jul30.145851.24...@access.digex.com> j...@access.digex.com
                (Jim Brooking) writes:
I've just got to jump in to the fray here.  As anyone who knows anything
can tell you, required power input increases with speed on almost any
vehicle.  Not only that, but the amount of power increases in  proportion
to the square of the speed.  Now that is not to say that some vehicles
might not produce a certain amount of power more efficiently at higher
speeds than lower (engine speed, that is), but as a general rule, the
slower you go, assuming that you're in the right gear, the less fuel
you're going to consume for a given distance.  Of course, there are
also aerodynamic considerations.  Too low a speed and the passage of the
vehicle through the air may produce more turbulence (ie. more power being
wasted churning up the air) than it would at a somewhat higher speed.
        As a general rule however, I would be surprised to see many vehicles
where fuel milage doesn't drop pretty much consistently with speed, once
above a certain speed (usually quite low-just fast enough to overcome the
static friction from bearings, rolling resistance, etc.)  However, your
mileage may vary :-) :-( .
        Anyway, later...
--
+--------------------------------------------------+----------------------- --+
|Ryan Craig: Comp Sci Co-op, Dalhousie University  |  Disclaimer: My opinions|
|cr...@ug.cs.dal.ca               are mine, all mine, and you can't have them|
+-------------------------------------------------------------------------- --+

This is one of the biggest crocks of shit I've read on this forum.
Just once, ONCE, I'd like to see a cop signal a lane change, or even an
outright turn for that matter.  I'd say that the cops are the worst
abusers of traffic laws in any situation.  I do not see them as "model
citizens of common sense driving".  The situations that most netters in
this thread are talking about are cops that go flying by at 80+ while
the rest of traffic is going 65-70.  In these situations, the other
stuff you list about "staying out of other people's way, do not block
his view, don't surprise him with sudden braking or manuevering" just
doesn't apply.  In fact, they come out of nowhere so quickly that they
usually do surprise people, scare the shit out of'em, more precisely.

Andy (Cops really piss me off) Brezinski
Intergraph Corporation
Huntsville, AL 35894-0001

On the other hand, you've got to admit that nothin' makes a hash of
things quite like a marked cop car driving an uneventful 55.  "Hello?
Officer?  Look, if you want to be grand marshal of a parade, wait 'til
the Fourth of July, OK?  We're trying to get where we're going -- like,
you, know, today or something!"  (What's REALLY funny, from a distance,
is the gang of idiots taking chances to get through the resulting
traffic jam, then standing on the brakes as soon as they see the cop.
Reminds you how few people even look beyond their own hood ornament,
much less think about what they see.)

Seriously, though, I suspect that the driving behavior of the local
gendarmerie depends heavily on the individual department.  Ditto for
a lot of other aspects of police conduct.  Like other people, they'll
pull as much nonsense, or as little, as they think they'll get away with.

--Joe
"Just another personal opinion from the People's Republic of Berkeley"

A few month ago I was driving at night on the TSP (Taconic State Parkway
in NY) returning from a business trip in Albany when behind me, very slowly,
a car with flashing grill lights (umarked car) slowly approached.  Now this part of NY is very rual and does not see much traffic late at night.
Deer are always around and I was tired so I was only doing 55-60. As the cop approached I figured he couldn't be after me because I had been keeping my speed down. (Normally people just fly down this section of the TSP). I kept my speed to 55. Still he appoached, but slowly - with grill lights flashing!
Now I have never seen this (or experienced this behavior before) when a
cop was going to pull someone over. When he got behind me (not close, but at a normal following distance) he just hung back and followed me. Did he want me
to pull over? Why was he hanging back? Did he not realize his grill lights were on? After a few miles of this I became very uncomfortable; I picked out
a good stretch of road with a level grassy shoulder (no paved shoulders
on this past of the parkway) and slowed down and pulled over, the cop did the
same. Now things get really interesting:

Cop: Why did you pull over?

Me:  Well, your lights were on when you came up behind me, when you stayed
        I figured you must want me to pull over.

Cop: Is everything all right?

Me: Yes.

Cop: Well, there's nothing I wanted (or somthing to that effect).

He returns to his cruiser and we set off, his grill lights still flashing!
Now I begin to wonder is this guy on something? This is almost like harassment!
We continue down the road like this for about 5 more minutes. Then, a few
other cars star approaching us (doing the normal 65-70). This is real
interesting because from behind they must not be able to see the cops
grill flashers. One by one they come zooming up only to see them hit the brakes
as they overtake the cop, slow down to our speed, and then fall in behind
the cop. This goes on for about a half-dozen cars over 15 minutes. I figure
they must think I some kind of idiot that can't see the cop behind me!
Eventually, he cop gets off the parkway and our little caravan (the
conglomeration, not the vehicle) disperses.
--
+-------------------------+
| Michael Amato           | ..I'm working on it......
| m...@philabs.philips.com |
+-------------------------+

In article <25...@dog.ee.lbl.gov>, jtc...@csa3.lbl.gov (JOSEPH T CHEW) writes:
|> ...                        (What's REALLY funny, from a distance,
|> is the gang of idiots taking chances to get through the resulting
|> traffic jam, then standing on the brakes as soon as they see the cop.
|> Reminds you how few people even look beyond their own hood ornament,
|> much less think about what they see.)
|>

That brings to mind a fatal accident I witnessed back in the '70's.  All 4 lanes
of the interstate were stopped while a tow truck had his cable stretched across the
road trying to pight an overturned tractor trailer rig.  Somewhere back in the
pack a motorcyclist decided he didn't like sitting still so he lane-split up
through the traffic.  Upon seeing the front of the line he cranked the throttle
wide open, not bothering to notice the cable stretched taut in front of him.  He
died.  I'll never forget that scene...

--
Alan Hepburn           "An ignorant person is one who doesn't know
National Semiconductor       what you have just found out."
Santa Clara, Ca              
a...@berlioz.nsc.com                              Will Rogers

OK, here's some physics.  Power = force x velocity.
Static friction is indeed often larger than sliding or rolling friction,
so it costs a large effort (but no power, because velocity is zero.)
to get something started. But once moving, practically everything
generating resistance, i.e. force the engine must overcome, is constant or increor increases with velocity. Engine friction, tire resistance, air
resistance is even proportional to velocity, so air drag goes like
velocity^2.  
        The apparent effect of inertia is to overcome small increases
in drag/resistance etc., like pushing a hand mower fast into a
deep patch of grass.  But you're just using up energy you put in earlier.

        I suspect the Lotus mentioned in the original article just had
a engine that was very inefficient at low speeds.  But if you
own a Lotus, who cares about gas mileage, anyway?
Pete Mason
.

Sorry, I misspoke.  Drag goes like velocity squared, so air drag
power goes like velocity cubed. The gas you burn is proportional
to power, so its pretty hard to see how a car could burn less gas
at 80 than at 40, unless that engine was horribly inefficent at
40.  But that's what a tranny is for.

Peter Mason

Actually, it's kinetic ENERGY that increases in proportion to the
square of the velocity.  Power, which is energy per unit time,
therefore increases in proportion to the cube of the velocity, I
believe.  An engine does not produce energy at a constant rate
throughout its range of RPM's; it will generally do poorly at the low
and high ends of the spectrum, and peak or plateau somewhere in the
middle, depending on the design of the engine.

In any case, the observation made by Mr. Brooking, that it is easier to
keep a body moving than to accelerate it, is deceptively obvious.
According to our friend Mr. Newton, F = ma, where F is the force
applied to an object, m is its mass, and a is its acceleration.  At
constant velocity, a is 0, and thus F is 0 (neglecting frictional
forces).  In order to change the car's velocity you must apply a force
proportional to the mass of the object, which (at low speeds) is much
greater than the frictional forces of drag.

Thus it is easier to keep a moving car moving (at low speeds) than to
start it moving from a standing stop.  It doesn't mean it's easier to
push a moving car; it just means that you're not accelerating a moving
car as much.
___________________________________________________________________________ _
Daniel A. Harling                        (harl...@pictel.com)
PictureTel Corp.             Opinions expressed are not necessarily those of
Peabody, MA  01960                 PictureTel, but they ought to be!

I won't get into the physics, but from riding bikes, its obvious that if
you pedal a fairly constant rate, you reach a maximum speed.  But if you
then change from an upright position to a tuck aero position, your
speed increases significantly which your pedaling input remains constant.
Now, assuming the government told the truth when they said 55mph gave good
gas mileage in the 70's, when car's were much larger, less aero, and had
less efficient engines, then shouldn't today's smaller, aerodynamic,
efficient cars be able to get their best gas mileage at a higher speed?

In your humble opinion, no doubt. ;-)

Fine, send me a blank videotape and I'll bring my camcorder out the next
time I go driving and make you a tape and send it back to you. ;-)

Again, that's your perception/opinion. You'd have a very hard time
proving it. Perhaps you could start with the accident statistics for
cops in your area versus the general population, i.e. how many accidents
per mile driven does an average cop get involved in versus the number of
accidents/mile for Joe Average Untrained Clueless Driver?

No doubt you believe that 90% of a cop's time is spent in just such
situations. ;-)

Well, at least you admit your bias (although it was painfully obvious
from the tone of your message).

In article <1992Aug7.053540.23...@cco.caltech.edu> pvma...@cco.caltech.edu (Peter V. Mason) writes:

It has to do with the volumetric effeciency of the engine at the rpm
necessary to achieve the speed in question.  
For instance, most engines get their best milage right around their torque
peak.  Because of this, it's definately possible for a car to get better
milage at 80 then at 55.  I used to own an '83GT that got 3mpg better
at 85 than at 65.  I tested it by identical 200 mile trips from Providence
to Lovel, Maine.  The trips were late night, with no traffic, so there was
no stop-&-go to mangle the results.
In both cases the car was in identical states of tune, with oil-changes and
new plugs both times, and they were within a month of each other in the
summer.  (so air-temp wasn't a factor)
I'd say 3mpg is a pretty significant...

--------------------------------------------------------------------------- -
        ___          
       / _ \                 '85 Mustang GT                        Bob Pitas
      /    /USH              14.13 @ 99.8                      bp...@ctp.com
     / /| \                  Up at NED, Epping, NH           (Cambridge, MA)

"If you go fast enough, driving in traffic is like driving in a parking lot"
Disclaimer: These opinions are mine, obviously, since they end with my .sig!
--------------------------------------------------------------------------- -

I don't think it's quite that simple; additionally you have the
gearing will determine at what speed the car will be going at a
particular rpm, and then you have building wind-resistance that will
chop away at the efficiency.  What I'd expect for most cars is a kind
of "mileage plateau" with one or two peak mileage points -- one at a
low rpm and velocity where wind resistance isn't so much a factor, and
one at higher rpms when the engine is running with enough power to
negate wind effects.

Although it's a statistical sample of one, experience with my own car
seems to agree with the theory.  I've found that my car has a mileage
curve where there are two peak mileage points -- one at about
45mph/35mpg (low rpms in 5th gear) and one at about 70mph/35mpg
(3000rpm, just after the start of the power curve).  There's a dip
between these points that bottoms out in the 55-60mph range where I
get about 2-3mpg less (32mpg).

It should be noted that the 55mph "saves gas" limit is not
particularly efficient on many sports cars, presumably because the
sports cars tend to have higher top-end gearing and better aerodynamic
profiles (and often relatively flat torque curves).  This was seen
during the mileage testing that preceeded the 55mph limit, but was
tossed out since so few people own Porshes et al.  55mph was chosed
because your average car got reasonably good mileage at that speed --
back in the early 70's.

Nowadays I imagine that you'd find peak mileage for your average car
at higher speeds -- the typical car has better aerodynamics and a
small engine with a peaky torque-curve that runs best at relatively
high rpms.

Hence 55 saves lives (a dubious statement IMHO) rather than gas.

Oh well, "this is the world we live in."

jim frost
j...@centerline.com