Wikipedia:Reference desk/Archives/Science/2011 September 22

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September 22

What are/ may be floating conditions to float any thing over water surface

Sir/ Madam I wish to know what are the floating conditions to make any thing float over water surface(Normal potable water not salty).

Wish for an early reply

Thanx a lot — Preceding unsigned comment added by 182.156.153.151 (talk) 04:20, 22 September 2011 (UTC)

Is this a homework question? 67.169.177.176 (talk) 04:45, 22 September 2011 (UTC)

For specifically FLOATING, you're probably after buoyancy. Vespine (talk) 04:47, 22 September 2011 (UTC)

(EC) For a large object in a stable configuration, the object will float if the mass of the object is no more than the mass of a volume of water equivalent to the portion of the volume of the object that’s below the surface of the water, i.e., the mass of the object is no more than the mass of the displaced water. See Displacement (ship) and Displacement (fluid). For very small objects, surface tension can cause an object to float even if it has a greater mass than the displaced water. Red Act (talk) 04:49, 22 September 2011 (UTC)

In other words, for all but the smallest objects, if the object's density is less than that of water, it will float. Very small objects (sewing needles, etc.) can sometimes float despite being more dense than water, because they are supported by surface tension. 67.169.177.176 (talk) 05:11, 22 September 2011 (UTC)

And, of course, an object can still float despite being made of materials far denser than water, like steel, so long as they contain a far lighter material, like air, beneath the waterline, so that the average density of everything is less than water. StuRat (talk) 06:25, 22 September 2011 (UTC)

And, with a more liberal interpretation of the word "float", we could include a hydroplane, hydrofoil, hovercraft, or ground effects airplane (only the first two actually require water). StuRat (talk) 06:36, 22 September 2011 (UTC)

Conditions:

1. Being Jesus.
2. Being an ice skater when it's cold
3. Any theologically admissible combination of the above. Cuddlyable3 (talk) 11:22, 22 September 2011 (UTC)

A solid sphere can float if the radius is less than

$R={\sqrt {\frac {3\gamma }{2\rho g}}}$

where $\gamma$ is the surface tension of water and $\rho$ is the density of the sphere. Count Iblis (talk) 16:02, 22 September 2011 (UTC)

Wouldn't $\rho$ rather be the density of the sphere minus the density of water? Dauto (talk) 21:06, 22 September 2011 (UTC)

If a vessel such as a nuclear submarine violated the "floating criteria" given by Red Act, as by having some compartments flooded, but had 200 megawatt nuclear reactors powering propellers driving it forward, and diving planes set to drive it upwards, couldn't it remain with a portion above the surface (of "potable water" such as Lake Michigan)? Would such a vessel be "floating?" This would be analogous to an airplane (as opposed to a "lighter than air craft" flying. Edison (talk) 04:15, 23 September 2011 (UTC)

To call that situation "floating" would be literary license at best, and abuse of terminology at worst. The submarine you just described is not "floating," it is "propelling itself upwards above the water." It's not buoyant. On the other hand, people do sometimes describe a heavier-than-air airplane as "floating," even in technical contexts like the FAA's Airplane Flying Handbook (Chapter 8, "Floating During Roundout," an undesired condition); but even then, the conditions are not due to buoyancy - it's used as an analogy to describe a dynamic effect. Nimur (talk) 04:55, 23 September 2011 (UTC)

OK, now I'm confused myself. What about a sub that's neutrally buoyant and cruising underwater at constant depth (say 60 feet)? Would that be considered "floating"? 67.169.177.176 (talk) 06:11, 23 September 2011 (UTC)

I think floating implies "less than" not "less than or equal to" if you see what I mean..Imgaril (talk) 10:40, 23 September 2011 (UTC)

So a neutrally-buoyant sub would not count as floating. 67.169.177.176 (talk) 19:59, 23 September 2011 (UTC)

Surface tension (mentioned above) is an impressive "floating agent." I tried the experiment of putting tapwater (density about 1 gm/cm² in a dish, and then placed placed a very large steel sewing needle (density about 8 gm/cm² on the surface, where it floated nicely. Edison (talk) 19:03, 26 September 2011 (UTC)

low boiling dopamine receptor agonists

Can someone help me brainstorm of new agonists I could use for fruit fly experiments? We've been working with cocaine for ... years and months, but I also want to try something else. For one, the success rate of aerosolising cocaine with a consistency amenable to experiment is rather unpredictable.

Feeding it into a test chamber by say, distillation often means the cocaine crashes out and crystallises on random surfaces, unable to be taken up by flies. For the love of the flying spaghetti monster, are there any agents better than cocaine that might be easier to administer through the air? (We cannot administer through their food, for various complex reasons.) elle _{vécut heureuse} ^{à jamais} (be free) 04:53, 22 September 2011 (UTC)

THC ? Nicotine ? Ethanol (might be a bit of an irritant, though) ? Or how about the chemical in some dry erase markers that just about makes me pass out ? StuRat (talk) 06:27, 22 September 2011 (UTC)

Those aren't dopamine agonists. While Methamphetamine and apomorphine have relatively low molecular weights, that's a lousy huristic for organic compounds, so what you really need is to go through Category:Dopamine agonists in CAS for an hour or two until you find something sufficiently soluble and volatile. 69.171.160.5 (talk) 06:52, 22 September 2011 (UTC)

Looking at the category on wikipedia - nearly all of those are essentially involatile - exceptions are amphetamine, and Propylhexedrine. These would need to be in the free base form - amphetamine is volatile enough to have a strong distinctive amine smell, and cause excitation if you leave the top of the bottle and smell it.. So it might create a great enough concentration in air naturally to affect your flies.

It's possible that there is dopamine agonist so potent that is it more effective than amphetamine despite lower volatility - but I don't know it - not my subject.Imgaril (talk) 13:17, 22 September 2011 (UTC)

Generally the way to introduce a non-volatile compound would be to convert to Aerosol form, generally using a Atomizer nozzle.Imgaril (talk) 13:36, 22 September 2011 (UTC)

The experiments are very sensitive to the size of the aerosol particles -- too big and the flies will simply not be affected by it! elle _{vécut heureuse} ^{à jamais} (be free) 21:41, 22 September 2011 (UTC)

Amphetamine free base looks like your best bet by far, and if you're already licensed for cocaine, it should be easy to come by. Are there any reasons it won't do what you want? 75.71.64.74 (talk) 21:48, 22 September 2011 (UTC)

Why are you trying to get flies high on hard drugs? 208.54.40.213 (talk) 04:56, 23 September 2011 (UTC)

I think she's trying to study the mechanisms of drug addiction. 67.169.177.176 (talk) 06:14, 23 September 2011 (UTC)

Does the pH of the environment affect crystallization rate? I'm wondering if you had a touch of ammonia in the atmosphere, would it stay in a free base form and be slower to precipitate out? (No idea if that works) Wnt (talk) 17:37, 23 September 2011 (UTC)

Cocaine boils at 187C (368F) - anything below that and it condenses out of vapour. If you start with the free base form it stays in the free base form, if you start with a cocaine salt and try to vapourise it I think it decomposes usually.Imgaril (talk) 21:19, 23 September 2011 (UTC)

My main concern was that if individual molecules pick up protons from some environmental source, would they make better nuclei for precipitation? After all, you say you see inconsistency and unpredictability, and it's not the boiling point that is changing. Wnt (talk) 03:36, 24 September 2011 (UTC)

Why does collagen cross-link in scar tissue?

After reading the scar tissue article, http://en.wikipedia.org/wiki/Scar, I came across this tidbit: "Sherratt et al, explain that scar tissue is the same protein (collagen) as the tissue that it replaces,[1] but the fiber composition of the protein is different; he explains that instead of a random basketweave formation of the collagen fibers found in normal tissue,[1] in fibrosis the collagen cross-links and forms a pronounced alignment in a single direction.[1] This collagen scar tissue alignment is usually of inferior functional quality to the normal collagen randomised alignment. For example, scars in the skin are less resistant to ultraviolet radiation, and sweat glands and hair follicles do not grow back within scar tissue. A myocardial infarction, commonly known as a heart attack, causes scar formation in the heart muscle, which leads to loss of muscular power and possibly heart failure. However, there are some tissues (e.g. bone) that can heal without any structural or functional deterioration."

I was wondering what exactly cause the collagen fibers to cross link and possible why the scar tissue replicates itself instead of normal skin since its constantly being replaced. Is there a specific gene for this? — Preceding unsigned comment added by 139.62.167.82 (talk) 20:42, 22 September 2011 (UTC)

I'm not sure that scar tissue does replicate itself. I think the same scar tissue may just remain with you for the rest of your life, similar to adult teeth (if they don't fall off). StuRat (talk) 04:31, 23 September 2011 (UTC)