Slashdot Mirror
Bang But No Splash
BishopBerkeley writes "When a drop of ethanol is dropped on a surface at low pressures (1/5 atmosphere or less), it makes no splash. Science offers a brief synopsis and fascinating pictures of the phenomenon. The results seem to confirm the (perhaps counterintuitive) prediction that more viscous liquids are more likely to splash, not less likely . Links to the researchers' home page at U of Chicago (as of now, the site is timing out) and pdf version of the article on arxiv can be found on the Science page also."
Fascinating. ----- Ut Tensio, Sic Vis
Ut Tensio, Sic Vis
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Full Text : Cho,Sucking Away the Splatter, ScienceNOW 2005: 4
Uh oh. Someone left some ethanol next to bored scientists again.
People like my friends know the right thing to do, but it appears that this knowledge is not common enough.
The creatures outside looked from Alt-Right to Antifa; but already it was impossible to say which was which.
" Your Subscription does not grant access to this item: Full Text : Cho,Sucking Away the Splatter, ScienceNOW 2005: 4"
Sounds like a whole different kind of webpage..
You cant fight in here, its a war room!
When a few drops of ethyl alcohol are dropped into a low-tolerance system, you get bangs, splashes, crashes, all kinds of stuff.
More study is clearly needed.
Click here to see.
Meh.
Isn't it amazing that we're investigating quarks but haven't yet fully understood the properties of athmosphere and vacuum? We could have found those phenomena 400 years ago, but no...
Makes one wonder what else the laws of physics are hiding from us yet... and whether we have really tried to analyse physics systematically enough.
(1 seems to be subscription only, other is alredy /.?)
Lets continue doing those experiments with alcohol ourself. In a plane. Mixed with lots of water (beer) , mixed with less water (jenever). Ans splashing.
Anything more useful to report about alcohol abuse?
When pointing out links that require subscription they shouldn't forget to mention it !
1 Drop splashing on a dry smooth surface Lei Xu, Wendy W. Zhang, Sidney R. Nagel* The James Franck Institute and Department of Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA. *To whom correspondence should be addressed. Email: srnagel@uchicago.edu The corona splash due to the impact of a liquid drop on a smooth dry substrate is investigated with high speed photography. A striking phenomenon is observed: splashing can be completely suppressed by decreasing the pressure of the surrounding gas. The threshold pressure where a splash first occurs is measured as a function of the impact velocity and found to scale with the molecular weight of the gas and the viscosity of the liquid. Both experimental scaling relations support a model in which compressible effects in the gas are responsible for splashing in liquid solid impacts. 2 What is the mechanism for the violent shattering that takes place as a liquid drop hits a smooth dry surface and splashes? How does the energy, originally distributed uniformly as kinetic energy throughout the drop, become partitioned into small regions as the liquid disintegrates into thousands of disconnected pieces? It is not surprising that the velocity of impact, the drop size and shape, or the liquid surface tension has an important effect on the mass and energy distribution of the ejected droplets [1, 2]. However, it is perhaps more difficult to imagine that the surrounding air has a significant role to play in this all-too-common occurrence. More to the point, one would hardly expect the splash to disappear if the surrounding atmosphere were removed. Nevertheless this is the case. The elegant shapes formed during a splash have captured the attention of many photographers since the remarkable early images of Worthington showing the shapes that occur as milk or mercury hits a smooth substrate [3]. Many studies have focused on the fingering dynamics [4 7] and the effect of surface roughness [1, 2, 8]. In the present study, we focus only on a drop hitting a smooth substrate. The top row of Figure 1 shows four frames from a movie of an alcohol drop hitting a dry glass slide in a background of air at atmospheric pressure. The drop, after impact, spreads and creates a corona with a thickened rim which first develops undulations along the rim and then breaks up due to surface tension. During this process, the thin sheet comprising the corona surface retracts and rips into pieces. These images are reminiscent of the corona caused by a drop hitting a thin layer of fluid photographed by Edgerton and his colleagues [9]. However, in our case we have made sure that the slide is completely dry prior to impact. Our images illustrate an important puzzle: why do we see a corona form at all? At the substrate surface the liquid 3 momentum points horizontally outward. Without a layer of fluid to push against (such as in the photographs of Edgerton), how does the expanding layer gain any momentum component in the vertical direction? Fig. 1. Photographs of a liquid drop hitting a smooth dry substrate. A 3.4 ± 0.1 mm diameter alcohol drop hits a smooth glass substrate at impact velocity V0 = 3.74 ± 0.02 m/s in the presence of different background pressures of air. Each row shows the drop at four times. The first frame shows the drop just as it is about to hit the substrate. The next three frames in each row show the evolution of the drop at 0.276 ms, at 0.552 ms and at 2.484 ms after impact. In the top row, with the air at 100 kPa (atmospheric pressure), the drop splashes. In the second row, with the air just slightly above the threshold pressure, PT = 38.4 kPa, the drop emits only a few droplets. In the third row, at a pressure of 30.0 kPa, no droplets are emitted and no splashing occurs. However, there is an undulation in the thickness of the rim. In the fourth row, taken at 17.2 kPa, there is no splashing and no apparent undulation in the rim of the drop. 4 Our experiment is straightforward: Reproducible drops of diameter D = 3.4±0.1 mm were released from r
It would be interesting to investigate how superfluids behave.
Since the article hints that the more viscosity, the lower the pressure must be to avoid splashing of the droplet, would superfluids (which have no viscosity at all) behave as expected even under the atmospheric pressure, or even a higher pressure?
Offhand, why are they using ethanol and not water for their study though?
Sucking Away the Splatter
LOS ANGELES--Nature may abhor a vacuum, but a vacuum abhors a mess. In the absence of air, a droplet of liquid can crash into a smooth surface without splattering, physicists report. The odd phenomenon might be useful for controlling droplet formation in technological processes like inkjet printing.
Splashdown. A drop of ethanol hits a smooth glass at atmospheric pressure (above) and 1/5 atmospheric pressure (below).
CREDIT: Lei Xu et al./The University of Chicago
It seems obvious and inevitable that a fast-moving droplet will splatter when it hits a hard surface. Researchers have studied the distribution of droplet sizes and energies in such splashes, and physicists Lei Xu, Sidney Nagel, and colleagues at the University of Chicago were searching for ways to control those sizes and energies when they discovered something unexpected: By pumping away some of the surrounding air they could eliminate the splatter entirely.
Within a tall vacuum chamber, the researchers released droplets of alcohol onto a dry glass plate from heights ranging from 20 centimeters to 3 meters. They recorded the resulting splashes with a high speed video camera as they varied the pressure in their apparatus, sucking it down as low as one hundredth of atmospheric pressure. The droplets struck the surface with speeds ranging from 2 to 7 meters per second, and for a given speed, the researchers found they could eliminate the splash by lowering the pressure beyond a specific threshold.
The team explains the results with a simple theory. As a drop strikes a surface, liquid begins to spread sideways at supersonic speed, creating a shockwave. The shockwave pushes back on the liquid, and if that force is greater than the internal forces holding the drop together, the shockwave will lift the liquid off the surface and create a splash. Reducing the pressure reduces the force exerted by the shock wave.
Ironically, the theory predicts that a thicker liquid should splash more than a thinner one. The researchers tested this curious prediction by studying the splash made by three types of alcohol with different viscosities. Indeed, the more viscous the alcohol, the lower the pressure needed to prevent splashing, the team reported here this week at a meeting of the American Physical Society.
"It's not uncommon to see a lovely phenomenon, but it is uncommon to get all the factors straight," says Walter Goldburg, an experimenter at the University of Pittsburgh in Pennsylvania. Bulbul Chakraborty, a theoretical physicist at Brandeis University in Waltham, Massachusetts, says the researchers' analysis opens the way to controlling splashing in, for example, spray coating surfaces with various substances.
They're just showing off how many servers they can crush.
- who or what is a Cho
I think it's supposed to be Chode Boy.
how 'bout I give you the finger....and you give me my phone call.
Ethanol turns into a thick syrup when cooled sufficiently. LN2 works nicely. And, yes, I've tried it. Just don't try to drink it.
reminds me of a chemistry department in a university. They do some testing on beer samples, but only require a few drops .. now what happens to the rest of the beer in the can or bottle?
important puzzle: why do we see a corona form at all? At the substrate surface the liquid momentum points horizontally outward. Without a layer of fluid to push against (such as in the photographs of Edgerton), how does the expanding layer gain any momentum component in the vertical direction?
That is an interesting question...sounds like a potential thesis for a few people out there.
A single data-point does not confirm. Inline with said theory? Sure.
Were that I say, pancakes?
The posting says:
"The results seem to confirm the (perhaps counterintuitive) prediction that more viscous liquids are more likely to splash, not less likely"
While the article says:
"Xu tested water splash as well. Water exhibits the same behavior, but its higher surface tension narrows the range of splash-forming impact velocity and creates a much larger margin for experimental error.
"It's much harder to splash than ethanol," he said."
Is say, this is a classic RTFA
http://www.hairykrishna.f2s.com/droplet.html
"Physics is to math as sex is to masturbation." -R. Feynman
Comment removed based on user account deletion
We invented nuclear bombs before we invented intermittent wipers for cars. Progress is never a smooth line.
The link given is to a login page, not to an article. It would be really nice if the editors caught these and filtered them out before posting.
The pictures were captured by the Phantom V7 camera at a rate of 47,000fps.
I wonder how long it will take to get a digital equivalent of this camera?
A bit faster than my Canon 10D! I want one!
Kevin
"It's not the cough that carries you off, it's the coffin they carry you off in" O. Nash
I tried a thought experiment. What would happen if I dropped a pail of marbles on the floor (this being like a liquid with zero surface tension). As each marble hits the floor it would like to bounce upward but it is constrained by the marbles above it. It would therefore tend to go horizontally. If I made the marbles sufficiently small and numerous, I suspect that I wouldn't see anything that looked like a splash. ie. the splash-like behaviour would be small in relation to the size of the 'drop'.
My question is this: If you made the liquid drops sufficiently small, would the behaviour change?
This was discussed in Science News (or maybe elsewhere) some time back so I'm working from memory. One of the things reseachers noted was that air was crucial for splashing. It's rather intuitive in a way. All of the momentum is downward, then converted to radially outward. What makes it go up? The leading edge of the droplet is rushing outward. With the right speed and gas pressure, it splashes up like popping the hood of your car while going down the highway. Get rid of the speed or the gas and it will stay low.
The world is made by those who show up for the job.
it looks like all the "splash" is created by the outward spread of the liquid from ground zero, it rushes outwards, but appears to "catch air" presumably because the surface tension / minimum stable raduis has been exceeded, and from that point on it becomes chaotic mixture of small droplets going every which way.
http://slashdot.org/~GuyFawkes/journal
"Researchers in the field previously had seen no reason for low atmospheric pressure to affect the results of their splash experiments."
researchers in the field must not know much about fluid dynamics and boundaries.
the liquid tries to displace the gas which is somewhat 'stuck' to the surface. lower pressure results in less mass to displace and less 'stickiness'. if the mess around with surface textures they'll see classical fluid dynamics variations. nano-scale aspects would make for interesting study.
You might also want to read the following papers:
A Comparison Analysis of the Greater Carbohydrate and Increased Photosynthetic Element Count of Budweiser Versus the Similar Enzyme Content of Bud Light
Next to medicine and biowarfare, brewing and fermentation technology is a major funding source for microbiology.
Some research suggests that drinking beer may stop your hair from turning grey
And possibly the most expensive PDF's in the world
Vintage computer adverts: http://www.vintageadbrowser.com/computers-and-software-ads
This is why you must never, ever, ever attempt to RTFA. It's just easier this way :)
Science at its best. Their explanation passes the three fingers rule. If a complicated subject can be distilled into a written answer that makes sense and can be covered with three fingers, that is elegance. However, don't be confused with answers that makes sense after ingesting three fingers of straight ethanol......
What would be great is to check this phenomenon out with computer simulation. It might be tough to set up though, since you'd have to deal with a compressible gas phase and incompressible fluid phase, and keep track of the fluid surface to account for surface tension. I'm sure it could be done though. Axisymmetric simulation would probably be fine to start off.
The world is everything that is the case
With that headline, I was secretly hoping they had photos of a tiny fireball. But nooooo.
Note: This printer has been designed to work in a low atomosphere environment for optimal ink transfers. Reduce air pressure to 17.2 kPa before printing else warrenty will be VOID.
I think the choice of words is a bit distracting...
I'm not a physicist, but even I can (seemingly) work this stuff out from first principles: a rubber ball bounces more than a brick because it's a soft body that can be bent, distorted, and recoiled by the forces involved in hitting the ground. Likewise, a more viscous liquid can hold in its forces more than a "lesser" liquid, and its shape will bend and distort as the forces (and fluid) push around inside it. Nothing counter-intuitive there to me.
Now, knowing something intuitively and validating it scientifically are two different things, and I (at least) wasn't aware that some liquids don't bounce, so I welcome this research of course. But I hope it leads to something a little more groundbreaking than that ;)
I'd also like to know if this ethanol is REALLY not bouncing all of a sudden, or if it's just bouncing less so that it becomes undetectable.
WOW!
Where are the pictures?
NEAT!
*gets back to work*
Please stop stalking me, bro.
Have a look at the PDF:
This equation predicts another non-intuitive result: a more viscous liquid splashes more easily than a less viscous one.
That's exactly the first thing I thought of. And this begs to be simulated.
It might be tough to set up though, since you'd have to deal with a compressible gas phase and incompressible fluid phase, and keep track of the fluid surface to account for surface tension.
You pretty much described what is done. The Navier-Stokes equations for compresible and incompressible fluids are used. But in this case air-compression is so low, that incompressiblity could be assumed. All of the difficulty here is tracking the surface and maintaining surface tension. From the equations you can read that the surface tension will depend on two things: pressure jump and the jump of the normal derivative of the fluid velocity. Possibly an artificial surface tension could be added that depended on the change of curvature of the interface surface.
I'm sure it could be done though. Axisymmetric simulation would probably be fine to start off.
Only recently, the preferred approach to date uses a method called the level set method. Here the interface is explcitly tracked. Problems arise here because originally the numerical methods and underlying mathematics that are used weren't set up for changing domains i.e. changing differential equations in the middle of a discrete spacial cell in (a finite element).
______________________________________________
sigamajig...
Can someone explain to me what the significance of this in the real world is? I'm failing to see this (honestly, I'm not trying to be a troll)
I was curious enough about what you said to do some further research. I found the following:
Protein denatures as you beat it up with the whisk Fat globules are dispersed into smaller and smaller droplets as well,,,hey, how would you like to be whipped with sharp slicing pieces of metal?????? All the while, water is swirling and moving creating eddies of air like a sunami in your bowl Sugar is looking for a safe place to land in all the confusion.... End Result: Uncoiled protein (denaturation) surrounds the air bubbles Sugar lands on the denatured protein and holds on for dear life Fat surrounds the sugar, protein and air bubble, trapping the water Now multiply this scene by about 2 zillion K-billion times You have created an interlaced 3-dimesnional net we call a foam (remember our dispersion chart???? Foam is a gas dispersed in a liquid.....air trapped in milk)
So you wouldn't be able to get the milk to turn into whipped cream which turns into butter without the air for the fat, protein, and sugar to cling to. So this is why the milk is shipped in a vacuum.
Full text: http://www2.muw.edu/~jfitzger/page81.html
I noticed that the drop that made the biggest splash was already distorted before impact. The drop that didn't make a splash was a perfect sphere up until the moment of impact.
I don't know about you guys, but this sounds like an effective form a birth control....
That reminds me of an experiment where they dropped thousands of ping pong balls down a slope to simulate an avalanche:
http://www.sciencenetlinks.org/sci_update.cfm?Doc
Consider dropping water through atmosphere. It can from a cup of water off a roof or even standing on a chair.
Slosh a large globule of water into the air and let it fall.
Watch it break apart after it reaches a certain velocity.
Wind resistance overcomes the surface tension of the water and scatters it.
I'd bet everything I owned that if you dropped the same globule of free-falling water in a vacuum it wouldn't break up like that after reaching a certain velocity.
(Though, the water would probably boil away in a vacuum or something, so substitute a different liquid for both experiments. Same effect, atomospheric resistance eventually overcoming any surface tension holding the free-falling globule together)
Applications could range from extremely fine dot-count inkjet printers to new vapor or liquid deposition manufacturing technologies. It could be a great way to make films and coatings for lots of things, including semiconductors.
I Pushed the plunger all the way, covered the tip with my finger and pulled out the plunger to create a vacuum. When I let go of the plunger the vacuum sucked the plunger all the way back. At equilibrium there was still no perceptable air space suggesting a pretty decent vacuum for a syringe.
I gets to thinking... What if this syringe can generate a sufficient vacuum to boil water? That would be a cool demonstration.
So, not having any water within arm's reach, I grab a bottle of 70% isopropyl rubbing alcohol and suck 5 ml or so into the syringe. I push out all the air, cap the end with my finger and pull back the plunger. I see bubbles! Maybe it's boiling! But when I repeat the experiment with the syringe upside down, I don't see any bubbles, so the bubbles must have just been an air leak at that end. Oh well.
So I squirt the alcohol out of the syringe and put it on a table, and forget about it.
This morning, I notice the empty syringe on the table. I wondered if water might work better, being more viscous. Maybe some vaseline around the end could stop any leaks. But when I pick up the syringe the end of the clear plastic device that had briefly held alcohol had shattered!
First of all this hard plastic was pretty hefty - 1/8 inch thick probably. Second of all, the syringe was right where I left it, It did not get knocked down or something. Why would alcohol make it shatter?
Around the plunger, I noticed a whitish semi-translucent o-ring that had broken at one spot. Maybe it was silicone? Possibly alcohol made that gasket swell and shatter the syringe? But it was a fairly soft gasket...
Why did the syringe shatter? The world may never know....
Wrong
Strange enough, axisymmetric simulation would probably of little use. Falling drops are one of those phenomena where a completely (or almost completely) symmetrical initial condition leads to a very asymmetrical result. In practice you do not get a circular 'wall' of fluid, but rather a kind of 'crown'. (Google came up with this example). The number of peaks of the crown has been investigated by someone, but I have forgotten who. More about symmetrical conditions leading to asymmetrical results can be found in the book Fearful symmetry.
If a drop of ethanol is dropped on a surface at low pressures (1/5 atmosphere or less), and nobody else is around to see it, does it make a splash?
"In an engine you break the gasoline into millions of pieces and then ignite them in a chamber, making a controlled explosion. You do that continuously in your car," Xu said. "A higher gas pressure might do a better job of breaking the fuel into smaller, more uniform pieces. But determining that would require further experiments more accurately simulating the splash process as it occurs under fuel-combustion conditions," he said.
- Give a man a fire and he's warm for a day, but set him on fire and he's warm for the rest of his life.
"splash-drop" effect.
I wonder what kind of splash a web server makes when it hits bottom? But yes, this article is a bit over the top. You can have good news, interesting news or slashdot news. Take your pick, but you can't mix and match.
The world according to SComps
water freezes/starts forming ice crystals at low pressures. Both would alter the conditions being examined.
I fear this will collapse into a joke thread, but seriously:
How would the shape of the well-known mushroom cloud change if the detonation occurred in a vaccuum? Would the characteristic double-shockwave be supported by the solids, or does it depend on the atmospheric pressure?
https://app.box.com/WitthoftResume Code: https://github.com/cellocgw
Man, the PDF's confusing enough. Don't do this to us!
Because reductionism is the only thing that works.
But beyond that, pretty much the definition of "fundamental" insures that knowing the actions of individual component particles is more fundamental than knowing the actions of large numbers of component particles, because the latter is a subset of the former: the rules specific to higher numbers of particles can be written in terms of those governing individual particles, but not always the other way around.
Wholism had its shot for the first 95% of human history. The last 5% has worked orders of magnitude better in much less time.
When a drop of ethanol is dropped on a surface...
I did my physics Ph.D. at Indiana U. with John Carini who did his Ph.D. at U. Chicago with Sid Nagel. That makes Sid my "academic grandfather"!
Sid has had a great career investigating processes that seem quite mundane and uninteresting on the surface but end up showing some quite interesting physics. Sid's experiments are often low tech (by physics standards) but quite elegant.
If only pee was less viscous - women would have one less thing to nag men about (I mean the bathroom floor, folks).
Wild ass guess, alcohol ruined the plastic.
...for this research. I can now freely drop all my ethanol without having to put on my safety glasses.
If you look at the pictures, the splash droplets are actually taking off, much like a plane, because of the air drag (they're moving fast sideways, some air gets underneath, therefore they take off).
If there's no (or little) air, the lift-off force is smaller, therefore they're less likely to take off.
That's pretty much like a high-speed boat (or car) tipping over because of the very high speed - if there wasn't air, it wouldn't tip over.
So does this mean that my 2 micron deskjet printer will have thinner (runnier) ink, and the process will occur in a vacuum? Kewel! If only week could keep the ink from bleeding in the fibre of the paper...
isopropanol might degrade some stuff, but if it had a bit of methanol in it that is much more likely to attack common latex seals
Because it's a non-Newtonian fluid. More specifically, it's a Bingham plastic. I wouldn't expect any non-Newtonian fluid to behave in a "normal" way. They don't flow like water (plug flow, rather than laminar) and have very funky properties, in general. It's complicated to discuss viscosity of a Bingham plastic, but I think ketchup is another example.
Si la vida me da palo, yo la voy a soportar Si la vida me da palo, yo la voy a espabilar
From here
A Natural Fission Reactor For thirty years it was assumed that the first nuclear chain reaction to occur on Earth was that set up by Fermi in Chicago in 1942. However, it has now been established that a natural reactor operated in a natural uranium deposit in west Africa 1.8 billion years ago. Evidence for this came in an interesting way. Natural uranium from Gabon was exported to France; an examination of the isotopic content showed that the proportion of uranium-235 was slightly lower than normally found This small difference was investigated and traces of the fission products of uranium were found in higher proportions than in normal uranium ore. This suggested that at some time in the geological history of the uranium, some of it had undergone a fission reaction. But how could a chain reaction have been established in natural uranium? The seam of ore, which was being extracted, was unusually rich in uranium-235 (up to 10 per cent). Geological conditions were responsible for accumulating large quantities in a small area. The water of crystallisation of the minerals in the ore might have acted as a moderator. It is now believed that a natural fission chain reaction must have taken place in the ore approximately 1800 million years ago. It may have run for just over 100 years, emitting a thermal power of tens of kilowatts (any greater power would have led to the evaporation of the water required as a moderator). In the course of its lifetime, it would have consumed a similar amount of uranium as a present-day power reactor consumes in a year.
Come on you guys - if you intend to post references to "News that matters", the least you can do is also publish a user name and password so we can read the friggin thing... there aint NO WAY I'm going to pay $10 to read any such references, and I'm sure other /. readers will agree - so whats the username and password please?
I can't believe you were modded up for this demonstration of missing the point. All that we've proved is that multiple Slashdot metamoderators cannot conceive of the possibility of 2 different factors affecting how much you splash.
The article demonstrated that, all else being equal, higher viscosity lead to more splashing. The article also noted that higher surface tension leads to less splashing.
If you understand the article, those points are completely separate. There was no implication anywhere that viscosity and surface tension are related. The connection between surface tension and splashing was understood before this experiment, the one with viscosity was not. Therefore they are talking about what was news.
But still to investigate splashing you have to pay attention to known factors (such as surface tension). And for picking a liquid for the experiment it helps to pick one that has low surface tension (ie not water).
Now with all that cleared up, I hope some moderators moderate down the parent and up the post previous to that. This is indeed a classic RTFA.
My guess is the bubbles were from an existing thin crack leak, and you exacerbated it by playing with vaccuum.
If you heat glassware with no liquid, it gets hair-fine cracks in it, and will shatter if you touch the (apparently solid) body. Glass is an amorphous solid similar to plastics.
Yea, except that increasing the pressure on the inside is the same as decreasing the pressure on the outside. The imperfections are still there and in either case you're simply creating positive pressure inside the balloon.
Imagine the first particles hitting the surface. They bounce directly perpendicular to the surface, but are blocked by other particles. These first particles are at the center of the impact zone and begin to pile up, creating a "cone" of particles. As more particles hit the cone, they slide off to the side, along with parts of the cone. Now, as the research hypothesizes, there is a "shockwave" of air particles resisting the outward motion. So these sloughing particles encounter this shockwave and again start to pile up, this time against the shockwave (horizontally). As more particles push up against the piled up particles, they "slough" off again in the only direction possible - upwards. It all comes down to particles running into and pushing around one another.
Do I get my Nobel Prize now?
I used perl years ago, and it's expressive, but I personally went the VB
route myself.
Where's the part of your theory where you explain why removing the air from the chamber makes the splash go away?
Patrick Doyle
I mod down every jackass who puts his moderation policy in his sig. Oh, wait a sec....
Actually fuel in any modern engine goes through the process of deflagration. While some may call this process a "controlled explosion" it would be more appropiate to call it the force produced by a combustion or burning of fuel.
A fuel explosion can connote a detonation which can not be controlled. Infact modern engines are extremely inefficient due to the avoidance of detonation (commonly called engine ping or knock), or in other words, their inability to harness the energy realeased by fuel detonation.
Otherwise, I understand your point and totally agree. We have much to learn.
As I understand it, the "trunk" of the mushroom cloud is caused by the in-rushing shockwave.
1. Bomb goes off and drives air away from explosion point in a hemispherical fashion (for a ground burst).
2. Air rushes back from all directions, but mostly at ground level where air pressure is highest.
3. This "squirts" the smoke and debris upward till either the air gets thinner or the in-rushing air stops. This creates the "stem".
4. At this point, the smoke and debris start spreading outward, creating the mushroom cap.
By the way - such clouds can be created by any large enough explosion, it doesn't have to be nuclear.
Clear, Dark Skies