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Interesting q about water
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. |
Interesting q about water
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. |
Interesting q about water
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 ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
Interesting q about water
"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. |
Interesting q about water
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 |
Interesting q about water
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 |
Interesting q about water
"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 |
Interesting q about water
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. |
Interesting q about water
"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 :) |
Interesting q about water
"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. |
Interesting q about water
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Interesting q about water
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. |
Interesting q about water
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. |
Interesting q about water
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. |
Interesting q about water
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. |
Interesting q about water
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 |
Interesting q about water
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. |
Interesting q about water
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 |
Interesting q about water
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Interesting q about water
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 |
Interesting q about water
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 -------------------------------------------------------------------- The more we gripe, * http://www.diversify.com/stees.html the longer God makes us live. * Graphic Design - Humorous T-shirts |
Interesting q about water
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 |
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