Wikipedia:Reference desk/Archives/Science/2013 January 10

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January 10

Hand grenade, part 2

What are the lethal radius, stun radius and injury radius for a German stick grenade? I want to know if that pesky German machine-gunner will end up killed outright or not. Thanks! (Oh, BTW, while we're at it, are these radiuses significantly affected if the explosion takes place inside a concrete pillbox?) 24.23.196.85 (talk) 00:25, 10 January 2013 (UTC)

Think of each radius as having a probability of stunning, injuring, or killing, not an absolute. StuRat (talk) 03:42, 10 January 2013 (UTC)

As for the pillbox, it will make damage must worse inside, both from overpressure and fragmentation (with pieces ricocheting off the walls), while those outside should be relatively safe, unless standing right by an opening. StuRat (talk) 00:40, 10 January 2013 (UTC)

So, how much damage can the enemy gunner expect to take (A) 8 feet from the blast (if he stays at his post), or (B) 15-20 feet from the blast (if he leaves his machine gun and retreats deeper into the pillbox)? Assume that in both cases, the blast happens inside the pillbox. 24.23.196.85 (talk) 07:06, 10 January 2013 (UTC)

A "pillbox"

(I am rapidly becoming an expert on stick grenades thanks to User:24.23.196.85's questions!)...The answer will depend to a huge degree on whether the year is before 1942 - when the grenade had a thin metal shell around the explosive - or after 1942 when the person who threw it could choose to place a "Splitterring" over the head of the grenade (or not). The Splitterring was a special cylindrical steel shell that wrapped around the grenade to increase the amount of fragmentation - at the cost of decreased blast radius. If the year is after 1942 and the person who threw the grenade had a splittering about his person and had appropriate training in when to use it - then they would certainly have used it against the pillbox.

There would be two main causes of injury - overpressure from the explosion and injury from the flying fragments. There might also be burn injuries. Inside a very tightly enclosed pillbox, the overpressure would be much higher than out in the open - and the fragments produced by the grenade would ricochet off of the hard concrete walls to produce a much deadlier effect...much more so if the splitterring was used.

The "effective blast radius" of the later model grenades (7oz of TNT) was 16 yards. The earlier models only had 4oz of explosive. Even if reduced by a splitterring - that would be ample to produce lethal overpressure in the confines of a pillbox. The victim might avoid the fragmentation effects if he could hide around a corner or in another chamber - but pillbox bunkers such as the one in the photo are typically nothing more than a hexagonal concrete box with some holes to shoot out of and a door at the back to get into and out of - so that's unlikely.

Best guess is that he's dead if he's 8 feet from the blast...and not many pillboxes are large enough to get 15 to 20 feet away...they really aren't that big. His only real chance is if this is a really large pillbox with an internal concrete wall and the thrower used a splitterring on a early Mk 24 grenade (with only 4oz of TNT) - which together reduced the blast radius by enough to keep the over-pressure survivable - whilst producing fragmentation that the occupant could avoid by getting into the adjacent room. But moving 15 to 20 feet away - and into another room - in the very few seconds available seems extremely unlikely! Hence, IMHO, he's dead no matter what.

SteveBaker (talk) 13:57, 10 January 2013 (UTC)

Part of the Atlantikwall in Ostend

The pillbox in your picture seems to be Czech but bears a striking similarity to the rather amateurish British Type 24 built in a panic the summer of 1940. The Germans. who liked to think of themselves as the masters of mobile warfare, were actually rather fond of hiding in the biggest and most elaborate concrete structures that the Organisation Todt could devise. Alansplodge (talk) 20:58, 10 January 2013 (UTC)

Thanks for the info, everyone! Just FYI, the pillbox I have in mind is of the half-moon type with access by bent entrance, and the gunner in question is manning the gun that is guarding the entrance to the pillbox; as for the grenade, it's a 1944 model (the scene takes place during the Battle of St.-Lo) without a Splitterring (the good guys here are Maquis, who generally didn't have access to such things). So the bottom line is, they'll find the gunner sprawling on the floor and as dead as a depth charge -- just like I thought. 24.23.196.85 (talk) 23:47, 10 January 2013 (UTC)

Oxygen, fire, and inorganic

1. Why do CO and CO₂ is classified as inorganic even when they have carbon atom in their molecule ?
   
2. What make oxygen a supporter of fire and carbon dioxide a detractor (non-supporter) of fire ?
   
3. What is difference between fire and flame ?
   

The articles are not much helpful. Want to be Einstein (talk) 06:16, 10 January 2013 (UTC)

1. CO and CO₂ are not of biological origin, though I'm not particularly good with the definition either.
2. Oxygen is a reactant in the combustion reaction we call fire. In most rate equations I've seen, fire's rate is greatly increased by the concentration of oxygen. This makes sense because the probability that oxygen molecules collide with fuel at sufficient speeds to cause a reaction is greatly increased. Likewise, carbon dioxide is an inhibitor which can act by decreasing this probability.
3. The fire article says that the flame is the visible part of the fire. There also exist non-visible parts of a fire, like the embers. Again I'm no expert with this definition.--Jasper Deng (talk) 06:25, 10 January 2013 (UTC)

1. The Wikipedia article Organic compound states it rather eloquently "The distinction between "organic" and "inorganic" carbon compounds, while "useful in organizing the vast subject of chemistry... is somewhat arbitrary". the ultimate answer is that there is not a good, sound reason for it besides the fact that its a historical artifact that has been dragged through the classification system. The article has some background of how they came to be excluded, but ultimately CO, CO₂ and the Carbonates are not considered organic just because. That's the best we can say, really. Sorry.
2. Oxygen atoms form strong bonds with other atoms. The stronger the bond formed, the more energy released in the process of forming it. So, just about any reaction that results in atoms that were formerly bonded to other atoms to bond to oxygen results in a large release of energy. The converse is true: to break bonds to oxygen, or to replace bonds to oxygen with bonds to other atoms, would require a huge input of energy. Thus, reacting a hydrocarbon with oxygen gas (forming water and CO₂) releases a bunch of energy, because of the formation of the stronger H-O and C=O bonds (compared to the original C-H and O=O bonds), and would require the same input of energy to reverse. Now, it isn't strictly true that nothing burns in CO₂; you just need to find a way to make a compound that is even more stable than CO₂. See This reaction of magnesium in carbon dioxide, a common demonstration.
3. Flame is the glowing gases in a fire. The fire is the entire reaction itself, including the solids and liquids and smoke and all together. It may be better to think of fire as the process and flame as the glowing gas. --Jayron32 06:45, 10 January 2013 (UTC)

Last time I checked CO₂ is respirated by biological forms; it is of biological origin. Plasmic Physics (talk) 09:53, 10 January 2013 (UTC)

Carbon monoxide is also biologically relevant. DMacks (talk) 14:40, 10 January 2013 (UTC)

The synthesis of urea (and other organic substances) from inorganic compounds refuted the idea that organic matter possessed a vital force

As noted in the article organic compound there isn't universal agreement on which molecules are "organic". Some textbooks, including one I had years ago, consider all carbon based molecules to be "organic", including CO2 and CO. I think it is more common to simply define some small carbon-based molecules as inorganic, but the set of molecules to exclude is largely historical and the result of drawing fairly arbitrary lines. For example, saying that "organic" molecules must have C-H or C-C bonds in them, while excluding molecules with only C-O or C-N bonds, even though the latter are also widely present in biology. Dragons flight (talk) 11:36, 10 January 2013 (UTC)

• The historical origin of the term is a common theme in books on the history of science. While many life forms do produce CO2, oxygen-carbon aerobic respiration is a late development so far as the history of evolution. That CO2 is found in nature without being produced by living organisms, unlike compounds such as urea provides the origin of the term. Originally, organic compounds were those that were only found in or produced by living organisms. Eventually it was discovered that those compounds almost universally contained carbon. The synthesis of urea in the lab was highly significant in the history of science, since it showed that no special vital force unique only to living beings as had been supposed was necessary for the creation of these substances.

The term has generally evolved to refer to hydrocarbons and their more or less complex derivatives in general and of whatever origin, given the hypothesis of a vital force was found false and unuseful. Whether one prefers the carbon-based or hydrocarbon-based definition is simply a matter of convenience. There are a relatively (!) small number of simple carbon compounds not containing any hydrogen, and their behavior is different enough from typical hydrocarbon derivatives that excluding them from consideration may be convenient, say, for biologists rather than chemists. μηδείς (talk) 20:32, 10 January 2013 (UTC)

Well, except that isn't strictly true. Carbon dioxide participates in reactions not unlike analogous "proper" organic molecules, for example it undergoes Grignard reactions, a common synthesis of carboxyls: R-MgBr + CO₂, acid workup --> RCOOH[1]) This is exactly analogous to the Grignard reaction with an aldehyde: R-MgBr + R'CHO, acid workup --> R-CHOH-R'[2]. --Jayron32 20:40, 10 January 2013 (UTC)

Are you talkin' to me? Hehe. I am not sure what you are denying the truth of, Jayron, something I said or someone else said. μηδείς (talk) 20:43, 10 January 2013 (UTC)

You stated "simple carbon compounds not containing any hydrogen, and their behavior is different enough from typical hydrocarbon derivatives...," which isn't really that true. In many ways, CO₂, one of the "simple carbon compounds not containing any hydrogen" does not significantly deviate from organic molecules in terms of its reactivity or behavior. Sure, CO₂ doesn't behave exactly like any other molecule, but only insofar as no two molecules behave exactly the same anyways, and CO₂s chemical properties behave pretty much as would be expected as if it were treated like an organic molecule. The Grignard example I gave above is representative, not exhaustive, of the way in which CO₂ works in organic chemistry. --Jayron32 20:50, 10 January 2013 (UTC)

Oh. Well, I am not myself saying that CO2 should or should not be excluded--it is a matter of convenience. I am quite aware that CO2 is a reagent in a lot of organic chemical syntheses. But the properties of CO2 are very different from hydrocarbons. The basic point is that historically, the term was used in a way that excluded CO2 for biological reasons, which is the strict answer to the OP's question. Nowadays chemists use the term synonymously with carbon chemistry. That doesn't befront me. μηδείς (talk) 21:00, 10 January 2013 (UTC)

First question is very important for me and it seems to be completely answered. Dragons flight said this "organic molecules must have C-H or C-C bonds in them, while excluding molecules with only C-O or C-N bonds". Is there any exception to this statement ? Please give some argument. Thank you! Want to be Einstein (talk) 16:51, 12 January 2013 (UTC)

Why is the ampere and not the coulomb an SI fundamental unit?

As a fourth year high school student, I'm currently studying high school physics. I know that the SI unit of charge is the coulomb while the SI unit of electric current is the ampere. They can be defined by each other (1 C = 1 As while 1 A = 1 C/s). However, it is the charge of an atom's protons and electrons which allow electric currents to occur in the first place. By this logic, shouldn't it be the coulomb and not the ampere that should be an SI fundamental unit, since the coulomb measures charges, and electric currents are just a manifestation of charges? Is this because of historical reasons, convenience or calculation reasons? Narutolovehinata5 ^tccsdnew 11:06, 10 January 2013 (UTC)

Yes, it is mainly for historic reasons. It is also easier in practice to measure a current than to measure a quantity of stationary charges. In calculations however, it doesn't really matter which is the fundamental unit. Oh, and I think you made a small mistake: (1 C = 1 As while 1 A = 1 C/s) - Lindert (talk) 11:24, 10 January 2013 (UTC)

As discussed in new SI definitions, there is a current proposal to define the electric charge as an exact constant with the effect that a Coulomb would represent an exact number of charges. Even so, the Ampere would still be considered the "base" SI unit for historical reasons. Dragons flight (talk) 11:41, 10 January 2013 (UTC)

Narutolovehinata5 has asked an excellent question. It demonstrates clear thinking about physics and units of measurement. Well done! Dolphin (t) 11:47, 10 January 2013 (UTC)

Last time I looked, the elementary charge, symbol e, value 1.602 176 565 x 10^-19 Colomb, IS a fundamental physical constant. What's fundamental and what is derived gets changed in the SI system from time to time as knowlege and measurement capability improves. Perhaps you are using an out of date textbook, or your texbook has regurgitated out of date information from another textbook. That happens very frequently in high school texts (and college texts too for that matter). It's importnat too, to understand the difference between standards and fundamental constants. While the ampere can be calculated from fundamental units of charge and time, the calibration of instruments will proceed from a primary standard apparatus held in Standards labs that provide a standard ampere. A known ampere can then be used to calibrate instruments that measure other things. See http://en.wiki.x.io/wiki/Elementary_charge Ratbone 121.215.62.231 (talk) 12:05, 10 January 2013 (UTC)

See SI base unit. The elementary charge is a basic physical constant (though not a fundamental constant), however it is not a base unit for the SI system. The original poster is correct that the Ampere and not the Coulomb / elementary charge is the basis of the SI system. Dragons flight (talk) 12:16, 10 January 2013 (UTC)

Hmmmm... The Wikipedia article I linked says in its second sentence "This elementary charge is a fundamental physical constant." It appears we have a conflict between two articles. I notice that the SI Base units article is based on the 2005 SI standard (Ref 1 in the article). The change was proposed back then. Was it not changed in 2007? Ratbone 124.178.177.177 (talk) 13:14, 10 January 2013 (UTC)

The 2005 (and later) proposals do not change the list of units defined as "base units" by the SI system, even though it would change how the Ampere is calibrated experimentally. Dragons flight (talk) 13:21, 10 January 2013 (UTC)

There is no conflict. The fundamental constant article clarifies the two distinct meanings for the term. Dauto (talk) 16:14, 10 January 2013 (UTC)

I don't understand why people are discussing the elementary charge, because it's irrelevant to the question. The ampere is a base unit because current is easily measurable and very commonplace in electronics, whereas charge is not. That's as much a historical reason as a current convenience reason.

Literally everything about the SI system--from its design, to its choice of units, to the continually-changing definitions of those units--are for the convenience of us humans. If we can't easily use a unit or reproduce its value based on its definition, it's useless, because the Universe couldn't care less about what humans use to describe it. --140.180.240.178 (talk) 05:00, 11 January 2013 (UTC)

Precor treadmill's interval settings

There are only Precor treadmills in my gym. I started my interval training this week. I plan to do high-intensity interval training maybe twice a week.

I noticed that Precor's presets are 2, 4, or 6 mins of work and 2 mins of rest. Some more advanced models are programmable but the model in my gym seems to be fixed. Very few people bothered to tweak the settings.

• http://www.trainingdimensions.net/tdArticles/Treadmill%20Manual.pdf

However, most articles that I have read about HIIT said that the intervals shall be much shorter in order to be very very intense. Such as Wikipedia's HIIT article:

The original protocol set a 2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking.

Many Android interval apps also have similarly burst settings.

Certainly I can do two minutes of sprinting. But I can run much faster if the interval is set to 30 seconds. Are the two minutes intervals compromise the HIIT? -- Toytoy (talk) 12:48, 10 January 2013 (UTC)

It's pretty dangerous to use a treadmill at sprinting pace, and especially to bring it up to sprinting pace very rapidly, or down from sprinting pace. If you want to follow such a protocol, I wouldn't do it with a treadmill. Looie496 (talk) 18:18, 10 January 2013 (UTC)

Agreed, you'd need a special much larger treadmill, to make falling off less likely, and nice soft surfaces on all the sides, in case you still managed to fall off at full speed. StuRat (talk) 04:16, 11 January 2013 (UTC)

If you can't keep up with the pace, running on the treadmill can be very dangerous indeed.

I wonder why the Precor 954i does not have some sort of alarm that flashes red light and makes a little noise to let you know it's going to get faster.

If danger is a reason why treadmills do not provide HIIT options, you can still set the treadmill to switch between 12 mph (the maximum speed) and 0.5 mph every two minutes. This can still be very dangerous. I use inclination change (0 to 5%) to get me notified. The Precor model allows up to 15% inclination. However, I think the gym disabled anything steeper than 5%.

OK, maybe next time I'll do HIIT on a stationary bike or an elliptical machine. They are not supposed to kill you. Otherwise I'll do HIIT when I am jogging (if the weather becomes a little better). I'll wear a heartbeat monitor just in case. -- Toytoy (talk) 16:04, 11 January 2013 (UTC)

How does the Mola Mola defend itself

A 3,500 lb specimen of the Ocean Sunfish, or Mola Mola

This fish is huge (up to 5,000 lbs) and ungainly, and supposedly non-toxic. It seems so much like floating meat it reminds me of this animal. Has anybody got any information on how it defends itself? Thanks. μηδείς (talk) 20:06, 10 January 2013 (UTC)

Did you read the second paragraph under "Life cycle" in our article? Deor (talk) 20:14, 10 January 2013 (UTC)

Yes, the point of it seeming to be they don't have any defenses. Kind of one of the Creator's cruel jokes, like the animal in the video I linked to. I realize the small ones have spikes. What I am curious of is if the large ones taste bad (in Asia they're a delicacy) or something else. Being big enough only to be a slow-moving shark and aquatic-mammal appetizer doesn't exactly strike me as a "defense". μηδείς (talk) 20:50, 10 January 2013 (UTC)

Of course, before there was the Ameglian major cow there was the shmoo (shmoo)... - Nunh-huh 03:45, 12 January 2013 (UTC)

Animals don't need "defenses". To persist as a population, they just need to reproduce more than they die (or about equally on average). Our article says that Mola Mola females "produce more eggs than any other known vertebrate." Sure, a lot get eaten, but some don't (see r/K selection). Also, fecund females can produce eggs over several years. This could potentially form a storage effect that buffers the population against bad bouts of predation, but that's approaching WP:OR.

We don't have an article on it, but the main thing governing species persistence is the long-term, low-density growth rate, which quantifies how strongly a population can "bounce back" after some perturbation to low density. You can search that term on google scholar to find several interesting articles, though they tend to be theoretical. From a more applied perspective, you may be interested in Population_viability_analysis. And really, their adult size does surely reduce their predation, compared to smaller fishes. Finally, you may enjoy these course notes on population growth [3]. SemanticMantis (talk) 21:55, 10 January 2013 (UTC)

You know, you are absolutely right, because although I noted the very high value of r, I was still thinking of them as a K-selected species because of their huge adult size. (It still amazes me that any of them live past the spiky fry stage.) And even though they are obviously r-selected, they may still have undesirable traits such as their skin, which is compared to color-changing mucus covered sandpaper. Their similarity to sea turtles, which also graze jelly-fish, is also interesting. μηδείς (talk) 23:26, 10 January 2013 (UTC)

Right, the article even mentions that sea lions kill them, but don't eat them, so maybe the skin is a taste deterrent... SemanticMantis (talk) 23:30, 10 January 2013 (UTC)

It still amazes me that any of them live past the spiky fry stage ... Does living with the jellyfish help them survive? I mean if you eat jellyfish, you probably spend much of you time living with them. Jellyfish around them may prevent them from being eaten by sharks. -- Toytoy (talk) 15:40, 11 January 2013 (UTC)

Yes, passive protection by their prey would be similar to clownfish hiding among anemones. Back to the r-selection, the growth rate of these animals seems incredibly huge as well, reaching adult size in a few years and not living past ten in captivity. μηδείς (talk) 20:38, 12 January 2013 (UTC)