The Naked Scientists

The Naked Scientists Forum

Author Topic: Are liquids really incompressible?  (Read 10135 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 11 times
    • View Profile
Are liquids really incompressible?
« on: 14/08/2012 17:30:01 »
Peter Eccles  asked the Naked Scientists:
   
Dear Dr Chris,

Thank you for a very interesting programme. May you continue for a very long time.

You were asked a question on the compressibility of water especially when it freezes and you agreed with the general mis-conception that water and other liquids are incompressible.  I fully understand that it would probably confuse lots of people should you go to that area, especially with the time constraints you have on the programme but I have found that most Hydraulic "Engineers" still believe that oil is incompressible, which is one of the first statements they are told in Basic Hydraulics.

I have often had to resort to "Google" to support the fact that George Constantinesco, a Romanian Engineer demonstrated a Silent Trench Mortar which was a Liquid Spring utilising water. It was capable of throwing a 90 kg bomb 1.4 km without a sound, even so the Ministry of Defence (War Office) walked away saying that "it was just the ravings of a mad Romanian" as everyone knows that water is incompressible and they never took this idea any further.

I do know that the Blackburn Aircraft Company incorporated a liquid spring in the main undercarriage of the Buccaneer which could absorb the immense shock of landing on an Aircraft Carrier at sea.

I am sure that you are fully aware of all this but for interest sake I find George Constantinesco was a very interesting man.

Peter Eccles

What do you think?
« Last Edit: 14/08/2012 17:32:42 by chris »


 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8646
  • Thanked: 42 times
    • View Profile
Re: Are liquids really incompressible?
« Reply #1 on: 14/08/2012 20:15:05 »
No, liquids are not incompressible, but the compressibility is usually too small to bother with.

About 5E-10 per Pascal according to WIKI
so, even at the bottom of the ocean 4Km down the change in volume is less than 2%
 

Offline chris

  • Neilep Level Member
  • ******
  • Posts: 5337
  • Thanked: 65 times
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: Are liquids really incompressible?
« Reply #2 on: 15/08/2012 13:42:16 »
So what happened to George Constantinesco's bomb launcher? Sounds intriguing. And what was the apparatus or set up he used?
 

Offline William McCormick

  • Sr. Member
  • ****
  • Posts: 153
    • View Profile
Re: Are liquids really incompressible?
« Reply #3 on: 18/08/2012 04:19:48 »
So what happened to George Constantinesco's bomb launcher? Sounds intriguing. And what was the apparatus or set up he used?

Very nice post.

http://www.gs-harper.com/Mining_Research/Power/sonics002.asp

I would bet they didn't want peasants and slaves to have those either. I wonder how much of that was expansion and spring loading of the metal container?

The right to bear arms seems to have a very important place in life.

I believe we sent x-ray generators over for World War One. They detach the tendons from the bone, they say that it is so painful.

After World War One, all the world powers agreed to never use, electronic weapons, chemical initiating explosives on one another, the list went on and on. I think the treaty that was signed, become top secret. After World War Two. 

Could you imagine a slave or peasant, having an opinion and the power to express it? I think that would make him a free man. Usually if you want your slaves or peasants to have an opinion you give them one.

                      Sincerely,

                            William McCormick
 

Offline survivalist13

  • Jr. Member
  • **
  • Posts: 15
    • View Profile
Re: Are liquids really incompressible?
« Reply #4 on: 18/08/2012 18:47:49 »
That article is very interesting. Although I guess that the high pressures involved would in most cases prevent it being cost effective.

It is a good point about how much could be due to metal distortions.

I can find no reference to x-ray guns used in WW1 or since. I doubt it is true as I wouldn't have thought they would detach tendons from bone, perhaps someone more biologically minded could confirm this. The only effect I can think of would be to cause cancer which doesn't seem like a very immediate or effective weapon. The only other possibility being a powerful laser, but these certainly weren't around in the first world war. If a treaty is top secret how would you know about it? Plus treaties can be ignored, the laws of physics not so much.

Now that I stop to think about it a right to bear arms is actually an interesting issue. Bearing arms in a free country is counter productive, as the drawbacks far outweigh the benefits. However if that country is on a world which isn't free then that country should be allowed to defend its self. It comes down to making it a level playing field, if one party has weapons and the other doesn't then one has an unfair advantage, if neither has weapons it is fair, and liberty should in most cases prevail as a more optimal solution, if both have weapons it is fairer but worse than if neither had any, as liberty is less effective at killing.
In conclusion English democracy > American Democracy :)
Got a little off topic there.
 

Offline William McCormick

  • Sr. Member
  • ****
  • Posts: 153
    • View Profile
Re: Are liquids really incompressible?
« Reply #5 on: 18/08/2012 23:08:03 »
That article is very interesting. Although I guess that the high pressures involved would in most cases prevent it being cost effective.

It is a good point about how much could be due to metal distortions.

I can find no reference to x-ray guns used in WW1 or since. I doubt it is true as I wouldn't have thought they would detach tendons from bone, perhaps someone more biologically minded could confirm this. The only effect I can think of would be to cause cancer which doesn't seem like a very immediate or effective weapon. The only other possibility being a powerful laser, but these certainly weren't around in the first world war. If a treaty is top secret how would you know about it? Plus treaties can be ignored, the laws of physics not so much.

Now that I stop to think about it a right to bear arms is actually an interesting issue. Bearing arms in a free country is counter productive, as the drawbacks far outweigh the benefits. However if that country is on a world which isn't free then that country should be allowed to defend its self. It comes down to making it a level playing field, if one party has weapons and the other doesn't then one has an unfair advantage, if neither has weapons it is fair, and liberty should in most cases prevail as a more optimal solution, if both have weapons it is fairer but worse than if neither had any, as liberty is less effective at killing.
In conclusion English democracy > American Democracy :)
Got a little off topic there.

Where we grew up, this was just part of the history of the United States. America and Germany both used the most insidious weapons on each other. The gases they used are so painful so destructive so disgusting to watch work, you have to wonder what the actual point was. Because nobody was going to win after that exchange.





This does not say that they used x-rays to hurt anyone on the battle field. However it mentions burns from X-rays. The technology existed at that time, and I was told by people that were in the war that, they did use such weapons, you name it, it was on that battle field, was their take on the war. It was so hideous that they actually tried to ban technology based warfare, after the war, with documents written to, ban such weapons on the battle field. The document from my understanding became top secret, because it listed all the weapons that you could use to create mass destruction.

However the x-rays at short range are totally debilitating, almost instantly. It causes a cooking effect of the bones. Those that have had it happen claimed it was the most painful thing that had ever happened to them.




                      Sincerely,

                            William McCormick
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4096
  • Thanked: 245 times
    • View Profile
Re: Are liquids really incompressible?
« Reply #6 on: 19/08/2012 00:06:43 »
Having recently celebrated Turing's anniversary, one application of the compressibility of liquids was discussed - early computers stored their data as sonic pulses in mercury delay lines.  http://en.wikipedia.org/wiki/Delay_line_memory

Silent guns might sound attractive - but what silent source would produce sufficient power? Nitrogen-based explosives have a very high energy density, and so can be easily transported to the battlefield, and quickly reloaded. Powering a gun by a human-powered pressure pump would result in a very low firing rate.

X-Ray tubes are pretty fragile, and require high-voltage power supplies. Because X-Rays go through most things, they are practically impossible to focus into a narrow beam; this would give them a very limited range. A conventional rifle with nitrate explosives would do far more damage at a greater distance, as well as being more transportable, rugged and reliable.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4096
  • Thanked: 245 times
    • View Profile
Re: Are liquids really incompressible?
« Reply #7 on: 19/08/2012 06:25:46 »
PS: Another shortcoming of water-cannons...

Much of the accuracy of modern rifles and cannons comes from the "rifling": a spiral pattern on the inside of the barrel. As the hot gases expand down the barrel, the spiral pattern imparts a spin to the bullet, stabilising it in flight, and improving the accuracy over the older smooth-bore guns.

Because the compressibility of water is quite low, it won't expand far along the barrel, so traditional rifling would be ineffective. This suggests that the accuracy of Constantinesco's launcher would be quite low (more like a mortar than a gun).

Another difficulty: In a conventional gun, there is a small gap between the bullet and the inside of the barrel, reducing wear on the barrel.

However, the compressed-water gun needs a very tight seal while the water pressure builds up, before firing. This suggests that friction with the barrel would slow down the projectile, and cause significant wear with every firing, making a tight seal problematical in the long term.
 

Offline Bored chemist

  • Neilep Level Member
  • ******
  • Posts: 8646
  • Thanked: 42 times
    • View Profile
Re: Are liquids really incompressible?
« Reply #8 on: 19/08/2012 10:02:25 »

Where we grew up, this was just part of the history of the United States. America and Germany both used the most insidious weapons on each other. The gases they used are so painful so destructive so disgusting to watch work, you have to wonder what the actual point was. Because nobody was going to win after that exchange.

This does not say that they used x-rays to hurt anyone on the battle field. However it mentions burns from X-rays. The technology existed at that time, and I was told by people that were in the war that, they did use such weapons, you name it, it was on that battle field, was their take on the war. It was so hideous that they actually tried to ban technology based warfare, after the war, with documents written to, ban such weapons on the battle field. The document from my understanding became top secret, because it listed all the weapons that you could use to create mass destruction.

However the x-rays at short range are totally debilitating, almost instantly. It causes a cooking effect of the bones. Those that have had it happen claimed it was the most painful thing that had ever happened to them.




                      Sincerely,

                            William McCormick


The reason for use of poison gas in warfare is very simple. It's effective.
There are certainly problems with it- not least people's perception of it.
However it's well documented that, during WWII it was given serious consideration.
http://books.google.co.uk/books?id=FmAhS0O1xvYC&pg=PT188&lpg=PT188&dq=calculation+made+as+to+how+it+would+pay+us+to+use+poison+gas&source=bl&ots=8mTX4y9Dkb&sig=BOzhAY1vhivDKmdLrkg6rGt7vfc&hl=en&sa=X&ei=tKkwUIWoEcaX0QWD7oD4DA&ved=0CEoQ6AEwAw#v=onepage&q=calculation%20made%20as%20to%20how%20it%20would%20pay%20us%20to%20use%20poison%20gas&f=false


One of the notable aspects of the use of gas is that it maims more people than it kills. Form a military perspective that's a great advantage. It drains morale and it ties up personnel looking after the injured (which is a lot harder than burying the dead).




However the idea that they could have used xray machines is somewhat laughable.
For a start, they are absurdly inefficient. Almost all the energy you put into them comes out as heat- rather than Xrays (does that sound familiar?)
Also there's no way that they would produce a specific effect like detached ligaments. They would have to  burn a hole in the skin to get to the ligaments first.
 


Again, things like this "However the x-rays at short range are totally debilitating, almost instantly. It causes a cooking effect of the bones.[size=78%] T[/size]hose that have had it happen claimed it was the most painful thing that had ever happened to them. "
don't make sense. The xrays can't reach the bones without damaging the tissues nearer the surface.
Also the inverse square law means that, if you were close enough to the enemy to zap them with xrays then you could probably hit them with a cricket bat. You would certainly be able to shoot them with a pistol (never-mind a rifle).
It just doesn't make sense as a weapon.
So, here's the challenge.
Identify the people you talk about.
Who said " it was the most painful thing that had ever happened to them. "?

As far as I know the only military uses of the compressibility of water are those that rely on sound travelling through it.
 

Offline Mazurka

  • Hero Member
  • *****
  • Posts: 510
    • View Profile
Re: Are liquids really incompressible?
« Reply #9 on: 21/08/2012 09:02:40 »
As far as I know the only military uses of the compressibility of water are those that rely on sound travelling through it.

Having been intrigued by this topic, I did a little googling about liquid springs and it appears that the most frequent use of them is for dampers & shock absorbers often of a military size and scale! 
 

Offline William McCormick

  • Sr. Member
  • ****
  • Posts: 153
    • View Profile
Re: Are liquids really incompressible?
« Reply #10 on: 23/08/2012 03:36:55 »
Having recently celebrated Turing's anniversary, one application of the compressibility of liquids was discussed - early computers stored their data as sonic pulses in mercury delay lines.  http://en.wikipedia.org/wiki/Delay_line_memory

Silent guns might sound attractive - but what silent source would produce sufficient power? Nitrogen-based explosives have a very high energy density, and so can be easily transported to the battlefield, and quickly reloaded. Powering a gun by a human-powered pressure pump would result in a very low firing rate.

X-Ray tubes are pretty fragile, and require high-voltage power supplies. Because X-Rays go through most things, they are practically impossible to focus into a narrow beam; this would give them a very limited range. A conventional rifle with nitrate explosives would do far more damage at a greater distance, as well as being more transportable, rugged and reliable.

Browning made slug guns, basically smooth bore shot guns with no choke. That were made to kill Tundra game, silently, so the whole heard would just think another Elk or Moose just dropped dead of the cold or hunger. Then you could pop another.

The slug is interesting, it actually has raised angled striation patterns on the slug itself, to spin it in the cartridge. When the slug is fired, it unrolls the plastic cartridge or casing, forward. Creating very high pressure between the slug and the casing and the gun barrel, because the casing is now double thick restricting and spinning the round. At this point the striations on the slug, force the slug to spin nicely. If you have ever seen a slug go in and out of an older model heavily made automobile in a perfectly straight line you know for sure what I mean. It will go through car doors, seats, and come out of a Z member on the other side of the car. In what looks like a perfect line of site hole in and out of the automobile.

One of the spring recoiling slug guns, by Browning Arms, would fire the slug silently, the only thing you could hear was, the very large stainless steel bolt, give off a slight ring. Almost like a hotel bell to call the bellhop. You can fire the same slug round, from a pistol grip Mossberg shotgun with one hand, and the recoil is not that impressive. But when you fired this Browning spring recoiling slug gun, with that round, it would actually cause hemorrhaging in the skin and flesh of your shoulder, no matter how tight you held the gun against your shoulder. I would compare it to a car accident. I could fire it maybe, ten times and then I would need a days rest to heal.

I believe it is the time the round stays in the gun, that actually causes the gases to start to contract. The barrel starts moving toward the shooter. So when the round comes out of the gun, there is zero pressure. There were two models that I know of, one was made in Belgium the other in Japan, both manufactured for Browning Arms. The Japanese, shorter barrel was silent, the Belgium barrel was longer and actually made a popping sound. Like when you slap your hand over your fully open mouth. It almost sounded like negative pressure. But that round was moving, and it flew straight, it was the most accurate round I ever fired. And it was smooth bore.

I have fired many rifles and handguns. But those two guns were just too comical to fire.

                      Sincerely,

                            William McCormick 



 

The Naked Scientists Forum

Re: Are liquids really incompressible?
« Reply #10 on: 23/08/2012 03:36:55 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums