You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.

Well, I won't claim I'm smarter than anybody - particularly in this group.

Here's my two cents on it. Consider a very large slow moving river and how
little damage it does (as long as it stays within its banks of course). It
erodes its banks very little and in fact may not have sufficient velocity to
maintain particulates in suspension causing it to become shallower with time
when upstream rains or floods fill it with sediment. As an example, a 100
foot wide river 5 feet deep traveling at a cross sectional average speed of
1 mile/hour (88ft/min) flows 44000 cubic feet per minute.

Contrast that with the output of a high pressure washer - ~four gallons per
minute (32 cubic feet/hour) at several thousand psi.

Or better yet, to tie this back to metalworking, compare the river with a
waterjet cutter. A simple description of these can be found he
http://science.howstuffworks.com/question553.htm

Regards,
StaticsJason


"daniel peterman" wrote in message
...
You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.

On Fri, 3 Mar 2006 19:30:19 -0800, (daniel
peterman) wrote:

You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.


Not an expert on hydrology, but after a snagging operation that
led to some erosions problems on a nearby stream I heard a hydrologist
testify that when a rivers flow velocity doubles, the erosion
quadruples. Croak in peace.....hopefully not soon..



ed

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"daniel peterman" wrote in
message
...
You guy are about a million times smarter than
I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive
force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think
the test was wrong.
It wasa long time ago and before I croak I need
somee finality on this.

The energy contained in a stream of water ( or
any fluid, for that matter) is calculated by
multiplying the mass flow rate in Kg/ sec times
the square of the velocity in metres / second..
From this calculation, you can come to the
conclusion that the faster it goes, the more
damage it does.

I hope that wasn't the exact phrasing of the question, because it is
unanswerable in that form. This is a problem in energy, i.e., physics,
and answers in physics almost always require quantities (*numbers*). So
a tidal wave (volume) is more destructive than a pressure washer, but a
hydraulic-mining jet is more destructive than a river.

You need the how-fast and the how-much numbers of each to compare. Or
relative numbers. E.g., "Which is more destructive: doubling the volume
or doubling the speed?"

Hmmm ... you need more than how-much and how-fast. You need
"concentration". A tidal wave 10 miles wide and 3 feet high is not the
same as one 1 mile wide and 30 feet high (each moving the same speed).
But, it's still a matter of numbers.

Bob

Daniel,

Like all open-ended engineering problems, the answer to this question
is: "That depends".

I ran into a similar situation many years ago during a thermo-dynamics
examination, set by a professor with degrees from Harvard and
Princeton. (Impressive but he couldn't teach worth a damn).

The entire exam revolved around the design of gas turbines and my
initial thought was that the time available was way too short: 3 hr
exam. Closer review of the questions showed serious shortcoming of
data.

I answered the entire exam with qualitative "here is how I would do it"
answers, describing my logic and thought process, but never supplying
one calculation.

The professor was ****ed at me but gave me a decent mark when I pointed
out what would happen on an official appeal, what with the "errors of
omission" on his paper.

Methinks I rambled somewhat?

Short answer: Describe the circumstanced under which each option would
prevail, ie. dominate. Even if the exam is of the true/false or
multiple choice type, write your answer on the side or back of the
sheet. You can then argue and substantiate your position on appeal.
Note that even text books get some of the answers wrong.

Wolfgang

"daniel peterman" wrote in message
...
You guy are about a million times smarter than I, but I got a
question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on
this.



In school I used to like to call these "what am I thinking" questions.
I am assuming the question might have had more detail, but possibly
not. But let me put it this way; If the energy in the high volume/low
pressure river is harnessed it can likely power 10 high pressure low
volume water jet cutters. Or one could approach the question as "what
do you mean destructive force? cutting a canyon out of rock and sand
over a few thousand years or cutting a .125 thick titanium plate in 10
seconds.

The next question is whether the question is asking for force or
power. If I have a tight lug nut on a wheel and I tie a 100 lb weight
on a 1 foot wrench I can exert a FORCE of 100ft/lbs of torque for 3
months, but there is no POWER transmission without movement.

Hope that helps

Bla

It was community college and maybe I was having an off day.All I could
think of was the Grand Canyon. That surely wasn't carved by high
pressure but rather large volume. And I kept thinkin' of glaciers which
are water that moves real slow but carves monster trenches in the land.
I hate community college.
Oh and yes I have sent hundreds of hours behind(thankfully) pressure
washer machines so every time I switched it on That stupid question
would come flooding back.

"daniel peterman" wrote in message
...
It was community college and maybe I was having an off day.All I could
think of was the Grand Canyon. That surely wasn't carved by high
pressure but rather large volume. And I kept thinkin' of glaciers which
are water that moves real slow but carves monster trenches in the land.
I hate community college.
Oh and yes I have sent hundreds of hours behind(thankfully) pressure
washer machines so every time I switched it on That stupid question
would come flooding back.
There you have one of the easiest answers to the question by example.
Consider the output volume of a pressure washer .. say washin a wooden deck.
Prety small compared to the volume of the garden hose hooked up to it. You
can run the garden hose wide open all day long and not even dislodge most of
the dirt. The pressure washer will rip the deck apart if you aren't careful
with way less volume.
And then the glacier example .. slow yes but tremndous pressure and the
grand canyon ... that ain't no slow meandering stream down there

"Bob Engelhardt" wrote: I hope that wasn't the exact phrasing of the
question, because it is unanswerable in that form. (clip)
^^^^^^^^^^^^^^^^^^^^
You are absolutely right, Bob. Usually, questions like this say (or imply),
"all other things being equal." But what are the other things? Equal
energy in both streams? Equal volume in both streams? Equal temperature?
etc. Usually, if the question is on a test for a course, you will be able
to guess what is wanted, just from the past lectures.

You will usually have the most trouble answering questions written by
someone less intelligent than you. They don't see many of the possibilities
that you do.

On Fri, 3 Mar 2006 19:30:19 -0800, (daniel
peterman) wrote:

You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.

Bad question. In order to have a clear answer it would have to
state destructive to what.

Tsunamis do enormous damage with volume flow. However, a water jet
cutter can cut materials that would be imervious to less pressure
regardless of volume.

If you direct a garden hose fed by 60 PSI water at your house, the
house will merely get wet. If a 30-foot high tidal wave ( 15 PSI at
the root) moving at 50 mph hits your house -- bye bye house!

"Don Foreman" wrote in message
...
On Fri, 3 Mar 2006 19:30:19 -0800, (daniel
peterman) wrote:

You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.

Bad question. In order to have a clear answer it would have to
state destructive to what.

Tsunamis do enormous damage with volume flow. However, a water jet
cutter can cut materials that would be imervious to less pressure
regardless of volume.

If you direct a garden hose fed by 60 PSI water at your house, the
house will merely get wet. If a 30-foot high tidal wave ( 15 PSI at
the root) moving at 50 mph hits your house -- bye bye house!

But the tidal wave is exerting way more total pressure on the house.

On Sat, 4 Mar 2006 10:12:07 -0800, "Glenn"
wrote:


"Don Foreman" wrote in message
.. .
On Fri, 3 Mar 2006 19:30:19 -0800, (daniel
peterman) wrote:

You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.

Bad question. In order to have a clear answer it would have to
state destructive to what.

Tsunamis do enormous damage with volume flow. However, a water jet
cutter can cut materials that would be imervious to less pressure
regardless of volume.

If you direct a garden hose fed by 60 PSI water at your house, the
house will merely get wet. If a 30-foot high tidal wave ( 15 PSI at
the root) moving at 50 mph hits your house -- bye bye house!

But the tidal wave is exerting way more total pressure on the house.

Total force, sure, because there is more area. Not necessarily
more pressure.

If water moving at 50 mph (73 ft/sec) is redirected to move
vertically, it would rise to a height of about 85 feet. s =
v^2/(2g) from high school physics and conservation of momentum. The
obstacle causing this redirection of momentum must therefore exert
the pressure necessary to do that, which would only be about 42 PSI.
Lower pressure but considerably more destruction.

Still begs the question of "destructive to what?" A pinhole leak in
a 2000 PSI hydraulic system, while having very low volume flow, can
easily inject hydraulic fluid into your eye. If it's your eye, you
may well argue that this is more destructive than getting doused with
10 gallons of fluid thrown from a bucket -- particularly if the bucket
isn't thrown along with the liquid.

Thanks for all the answers to this vex.
I know I was right in my reponse but it only cost me a few points..
I guess I shouldn't lose sleep over the thing.
Anybody wanna buy my nice Atlas 6 inch lathe. or palmgren rotary 8 inch
table.
I can ship the rotary table. Non tilting.
Not trying to be a merchant. just don't want to junk this stuff.

I think you should post this as a new message, it may be lost in
its present response position. I'm sure anyone having an interest
would first like to know what country you are in, and perhaps what
general part of that country you are in.
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"daniel peterman" wrote in message
...
Thanks for all the answers to this vex.
I know I was right in my reponse but it only cost me a few
points..
I guess I shouldn't lose sleep over the thing.
Anybody wanna buy my nice Atlas 6 inch lathe. or palmgren rotary
8 inch
table.
I can ship the rotary table. Non tilting.
Not trying to be a merchant. just don't want to junk this stuff.

Fair enough.
I am in San Diego California. The q still stands and all the answers
seem valid and well thought out.. Kindalike the what is it set by RH
with his pictures. I have many unusual objects and pictures of them as
well just no way to upload..
Fun stuff anyway.
I have things I'm not sure of the origon or what they do.

daniel peterman wrote:

You guy are about a million times smarter than I, but I got a question
wrong on a test years ago and it nags at me.
What would seem to be the more destructive force.
High pressure water or:
Massive water flow. IE volume
I guessed volume but it was wrong but I think the test was wrong.
It wasa long time ago and before I croak I need somee finality on this.

Look at New Orleans with massive watet flow.

John

Id say speed.

Lets say instead of viewing rivers and such... we put it in vacuum, and
in space (like all good theoretical physics questions..) We take two
blobs of water, one with 2x the volume (and therefore mass) and one
with 2x the speed (or v.. same thing if same direction) answer is
simple. 1/2mv^2. v^2 is a second order term, and therefore increases
faster than m.

(this assumes that Ke is the only limiting factor ... which Im guessing
is pretty close.. so "all else being equal, a higher velocity stream
will be more destrictive" )

Yes glaciers can erode mountains, but they're order of magnitudes more
massive.. give me a waterjet of that velocity, and i'll cut you your
mountain.

Yes sir I just can't quite grasp the entire physics. There was done and
documented a process called hydraulic mining here in Calif.
These large water cannons would blast away shale and sluice it down to
find gold.
They could shoot water a quarter mile.
I guess the gold deposits ran out.
Maybe the had some dry years as often happens around these parts.
They were called monitors

On Sun, 5 Mar 2006 03:41:02 -0800, (daniel
peterman) wrote:
Yes sir I just can't quite grasp the entire physics. There was done and
documented a process called hydraulic mining here in Calif.
These large water cannons would blast away shale and sluice it down to
find gold.
They could shoot water a quarter mile.
I guess the gold deposits ran out.
Maybe the had some dry years as often happens around these parts.
They were called monitors
==============================
Because of the damage downstream the runoff was doing to the
farm/pasture land this was banned. This was before "one man -
one vote" and the farmers/ranchers still had considerable clout
in the California legislature.

Unka George

Everyone is talking around the basic concept of energy and velocity.
E=Mv^2. The energy is the mass times the square of the velocity, in
consistent engineering units, which leads to the startling concept,
E=Mc^2 where c is the velocity of light, revealed by a fellow named A.
Einstein I beilieve.
Bugs

On 5 Mar 2006 08:52:27 -0800, with neither quill nor qualm, "Bugs"
quickly quoth:

Everyone is talking around the basic concept of energy and velocity.
E=Mv^2. The energy is the mass times the square of the velocity, in
consistent engineering units, which leads to the startling concept,
E=Mc^2 where c is the velocity of light, revealed by a fellow named A.
Einstein I beilieve.

That's "Norman Einstein" according to Joe Theismann, Bugs.

see cite below:
http://www.smithappens.com/dumbathletes.php



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Bugs wrote:

Everyone is talking around the basic concept of energy and velocity.
E=Mv^2. ... which leads to the startling concept,
E=Mc^2 where c is the velocity of light, ...

Except it's _1/2_ mv^2. Tantalizingly close, but not the same. Bob