Wikipedia:Reference desk/Archives/Science/2015 January 26

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January 26

What is the amount of gs in space???

My google-fu is failing. What is the amount of G(s) on Interplanetary space?201.78.189.0 (talk) 10:33, 26 January 2015 (UTC)

If you are talking about G-force (which is not actually a force) it can range from nothing to degrees that would rip you apart. It is a measurement of acceleration - the faster the acceleration the higher the gs. G-force can also be referred to as the acceleration felt as weight. If you are travelling at a constant velocity (in a straight line) in space you will experience 0 gs. 196.213.35.146 (talk) 12:24, 26 January 2015 (UTC)

You might be thinking of a gravitational constant, in which case you want to read about microgravity. In the vast emptiness of space, far from any massive objects, the acceleration due to gravity is very small, but not zero - so zero g is the wrong term, but people use it anyway. SemanticMantis (talk) 14:20, 26 January 2015 (UTC)

Also note that if you are in orbit about a body, that cancels the gravity from that body. So, if you started midway between the Earth and Venus, but not in orbit around the Sun, then you would be pulled towards the Sun. If you were in orbit around the Sun, you would not be. StuRat (talk) 15:06, 26 January 2015 (UTC)

Likely better to say "balances" rather than "cancels" and the fact is that, for example, the Earth is constantly "pulled towards the Sun" if one is literal.Collect (talk) 15:18, 26 January 2015 (UTC)

Indeed. Gravity acts on all objects that have mass: everything is pulled toward the sun. Some objects have immense angular momentum, due to their initial velocity, and this momentum must be conserved. So, these objects - even the ones in stable orbits - are still pulled toward the sun. Objects in stable orbits are in a constant state of acceleration - but they follow an elliptic trajectory (or a more complicated trajectory, depending on their velocity and other imperfect conditions).

The equation you want to use to find the force of gravity is given in our article, N-body problem#General_formulation. If you are in "interplanetary space," you may be able to neglect all objects except the sun.

Nimur (talk) 16:29, 26 January 2015 (UTC)

Is it possible the OP meant amount of gas in outer space? This source quotes others, and gives estimates about 1 atom per cubic centimeter. μηδείς (talk) 17:54, 26 January 2015 (UTC)

If it was, (s)he mistyped it twice, once with parentheses...I don't think it could have been a typo. SteveBaker (talk) 18:52, 26 January 2015 (UTC)

I swear I read the question. μηδείς (talk) 18:56, 26 January 2015 (UTC)

Meh...s(h₁)^t happens! 23:33, 26 January 2015 (UTC)

Yes I was/am talking about gravity, the one that on earth is 1 (http://en.wikipedia.org/wiki/Standard_gravity )201.78.189.0 (talk) 10:31, 28 January 2015 (UTC)

Genetics of Labrador Retrievers

Labs have three colors Black, chocolate, and yellow.

Is the Black color gene dominant over the other two color genes? I would say yes.

If so, does that make a black Labrador more genetically inclined to perform better as a Lab then a chocolate or yellow? why?

I would say all Labs would have the same or similar genetic traits with different color genes and all colors would perform at the same level. If that is right, why?

158.68.66.254 (talk) 16:20, 26 January 2015 (UTC)

Do you have any questions that aren't resolved by our article, Labrador Retriever coat colour genetics? Nimur (talk) 16:36, 26 January 2015 (UTC)

Although it's not mentioned in the article, some dog breeders will suggest that lighter puppies tend to be more highly strung. This is expressly mentioned in controversial book The Bell Curve by Herrnstein and Murray. RomanSpa (talk) 17:48, 26 January 2015 (UTC)

• You might also want to look at black dog syndrome, which is not a question of performance, but a bias against blzack dogs. Anecdotally, my blonde German Shepherd escaped while in heat, and mated with a purebred Black Lab. She had three puppies, two pure black, and one chocolate colored, but it was stillborn. You'd have sworn the surviving puppies were pure Labs by the look of them. μηδείς (talk) 17:50, 26 January 2015 (UTC)

It's spelled "blizzack", dog. InedibleHulk (talk) 00:56, 27 January 2015 (UTC)

It's been said that a lab is the closest thing we have to an "average" dog...(one reason why labs are so overwhelmingly featured on dogfood packaging)...so crosses tend to veer towards looking a lot like purebred labs.

Lab color is caused by three separate genes - and thus to call one color "dominant" is at best a wild over-simplification! Yellow labs actually split into two separate genetic groups - one with black skin and the other brown (most noticeable on their noses) - which also complicates matters. Some people distinguish "red" from "chocolate" and there is a genetic difference there too. There are also other lab colors out there: charcoal, silver and champagne...there is much dispute in the lab fanatic community as to whether these should be considered pure bred or not...but it's very easy for one of those non-standard colored dogs to have black/yellow/chocolate puppies and that complicates the genetics still further.

Anecdotally: I've had both black and yellow labs in the past - they all had different temperaments and I wouldn't say that there was any obvious correlation with color. Our last black lab had a bad time in Texas summers, that black coat can heat up to the point where you can hardly bear to pet them - so his enthusiasm for outdoor play in mid-summer was definitely a "color-related performance" thing. So we went with yellow this time around. Our yellow lab has been super-calm since day #1, so if there is a genetic link, it's gotta be a fairly weak one - but possibly because he was bred from a long line of hunting dogs where calmness is a valued trait.

But behavior is much, much more likely to be "nurture" than "nature". But when you're asking if a dog might "perform better"...you have to ask "better at what?"... Playing fetch? Being a gun dog? Being a drug-sniffer or a seeing eye dog? Tolerance for grandkids yanking on his tail and hoping he'll play "horsey"? There is just too much scope here to come up with a coherent metric.

SteveBaker (talk) 18:49, 26 January 2015 (UTC)

Coriolis force effect on a rifle bullet

Is the Coriolis force a significant factor in the impact point of a rifle shot over a 1000m range? I know that it is taken into account for aiming artillery and mortars but is it meaningful for long range rifle shooting? Roger (Dodger67) (talk) 20:40, 26 January 2015 (UTC)

Coriolis acceleration is equal to $a_{c}=2({\boldsymbol {\omega }}\times {\boldsymbol {v}})$, where $\omega \sim 10^{-5}\,s^{-1}$ and $v\sim 1000\,m/s$ (for rifle bullet speed). So, the acceleration is about $2*10^{-2}\,m/s^{2}$. Over 1000 m range (travel time about t=1 s) the impact point will be shifted by $d=a_{c}t^{2}/2$ or by about 1 cm. Ruslik_Zero 21:01, 26 January 2015 (UTC)

I think there is a mistake here: the angular frequency is 1/86400 per second, so $\omega =2\pi /86400$. Then the deviation would be more like 6.3cm, close to the three inches in the article below. --Mark viking (talk) 22:10, 26 January 2015 (UTC)

Minor correction: the angular frequency is 1/86164 per second. The relevant "day" is the sidereal day, i.e., the time for one rotation of Earth on its axis, not the calendar day. (This is a very common oversight.) Short Brigade Harvester Boris (talk) 01:13, 27 January 2015 (UTC)

Good point, thanks. --Mark viking (talk) 01:16, 27 January 2015 (UTC)

This is a topic in external_ballistics and a little info can be found in External_ballistics#Coriolis_drift. This article claims a three inch deviation at 1000 yards at 45 degrees north latitude due to the Coriolis effect. --Mark viking (talk) 21:01, 26 January 2015 (UTC)

As a simple sanity check, consider a bullet fired from the South Pole. The range of 1,000 m means that it strikes somewhere along a parallel of latitude at that distance from the pole. Pretending the Earth is flat (it's close enough for this purpose), the length of that parallel of latitude is 2π × 1,000 m or about 6,283.2 m. In one sidereal day of 86,164 seconds, a point on that parallel travels that distance. Therefore in 1 second it travels 6,283.2/86,164 m, which is 7.2921 cm—similar to the other amounts given above. --65.94.50.4 (talk) 05:54, 27 January 2015 (UTC)

Actually the travel time for a rifle bullet over 1000m is closer to three seconds than one. It may depart the rifle at about 1000m/second but deceleration is quite severe - the velocity at the 1000m mark is on the order of 1/3 to 1/4 of the muzzle velocity (depending on the caliber and bullet type). Roger (Dodger67) (talk) 13:31, 27 January 2015 (UTC)

Notice for small distances (such as the distance a bullet can travel), to a good approximation the deflection depends only on the distance traveled and not on the speed of the bullet. Short Brigade Harvester Boris (talk) 00:21, 29 January 2015 (UTC)

Fly eggs everywhere?

My local newspaper has an article discussing a past incident: in early July some years ago, local police found a car in which two people had committed suicide by carbon monoxide poisoning, and over the days since that time, fly eggs had hatched, and the car was full of flies feasting on the decomposing bodies. Is it common for fly eggs to be found in places like cars that generally don't have any non-microscopic organisms, i.e. is it likely that flies would have laid eggs in the car before the people had gotten in? I don't see any other alternative, as a space from which carbon monoxide molecules can't escape should be impervious to flies, i.e. I can't imagine the flies getting in postmortem. Nyttend (talk) 20:47, 26 January 2015 (UTC)

I would be very surprised if the car were airtight. I don't know what the source of carbon monoxide was, but presumably it was generated in sufficient quantities that it led to the individuals' deaths before it dispersed from the car - it doesn't take that much carbon monoxide to kill someone. It is likely that the flies were attracted by the scent of decomposing flesh that also dispersed from the car. I would also be surprised if the car were flytight (if that's a word). The flies could have found their way into the car and to the bodies postmordem and then laid their eggs on the dead bodies. Gnome de plume (talk) 21:09, 26 January 2015 (UTC)

But if the car's not airtight, wouldn't the CO simply escape out the windows instead of building to the low-yet-lethal levels that it obviously reached? The car was found in the woods, not in someone's garage, if that's at all relevant. Nyttend (talk) 21:24, 26 January 2015 (UTC)

Flies can get through very tiny gaps when they are attracted to decay odours. The gaps would be too small to allow gases to exchange quickly by diffusion. Dbfirs 21:30, 26 January 2015 (UTC)

In general, given a well-mixed volume with well-defined entrance and exit flows, the concentration of gases inside the volume will gradually approach the average concentration of gases at the inflow. This makes sense since whatever is inside must gradually be replaced by whatever is coming in. In general, there might be multiple inlets and outlets, but if the flux-weighted average concentration of CO across all the inlets is lethal, then eventually the concentration of CO inside will also be lethal. In general, CO ought to be dissipated at the tailpipe and loss on the wind; however, I can imagine a leaking emissions system could have been blowing gas into the engine compartment from which some of it could easily have found its way into the main body of the car. Dragons flight (talk) 02:41, 27 January 2015 (UTC)

The CO in engine exhaust, if it escapes before reaching a catalytic converter, is 20-50 times the minimum lethal concentration, so you wouldn't need that much of a leak to start causing problems. Dragons flight (talk) 02:48, 27 January 2015 (UTC)

• Can we have a link to the article? μηδείς (talk) 21:29, 26 January 2015 (UTC)

• You can, but it won't help you. Nyttend (talk) 22:11, 26 January 2015 (UTC)

Cars are not airtight, by design. Older cars may develop new gaps, through rust or rough use. Speed holes make the flies lay faster. InedibleHulk (talk) 21:58, 26 January 2015 (UTC)

Oh yes, I remember the old Beetle. You had to open a window to be able to close a door! Dbfirs 22:08, 26 January 2015 (UTC)

Also keep in mind, carbon monoxide is slightly lighter than air, and flies can steer. More paths for them to enter than for it to leave. InedibleHulk (talk) 22:01, 26 January 2015 (UTC)

Right. As a thought experiment: consider a car with that is airtight, save for one 1/4" hole in the side. That's not much air exchange to let fresh air in, but it is plenty enough to let putrescine and cadaverine out into the air. That will distinctive odor attract flies from quite a large area. And if it's been more than about 10 days or so (time to maturity for many fly spp.) then you're potentially contending with multiple generations of flies, growing exponentially in that period. Also consider that CO comes from car exhaust, which is usually outside the car. If it had been tampered with to let exhaust into the cabin, then there's your holes big enough for flies to get in. Death by CO (or any gas) doesn't require a hermetic seal - it only requires an input rate higher than the output rate, for long enough to get to the lethal concentration of CO. SemanticMantis (talk) 22:07, 26 January 2015 (UTC)

To directly answer your question about fly eggs - no, it would not be common for eggs to be there first. Most flies lay eggs in fruit, feces, carrion, and other common larval food sources. This is the reason why larva are useful in forensic entomology - the eggs don't show up until the person is dead, and if you know enough about the critters you can often get some good estimates of time/day of death. SemanticMantis (talk) 22:07, 26 January 2015 (UTC)

Every car I have worked on has a cabin air exhaust vent. These typically have dust traps or grids, but not mesh over them (I don't know why). So if the smell can get out a fly can get in. No, it would be unusual to see fly eggs (housefly eggs are surprisingly big) just lying around, they are tasty morsels.Greglocock (talk) 23:00, 26 January 2015 (UTC)

They also hatch almost as quickly as you can notice them. Not lying around for long, especially with bot flies. My last four dead dogs, like clockwork, shat themselves the day before and had maggots by funeral time, the morning after. Extremely impatient ghouls. And dysentery-style shit is about as pervasive and unique a scent as corpse smell, but faster. Newspaper reports (and most media) tend to avoid mentioning what condition the deceased's pants were in, but even a regular dump will speed up the process in a locked car. Farting while alive in one is bad enough. InedibleHulk (talk) 00:46, 27 January 2015 (UTC)

Yea, farts are a good example. If you fart in a car, the smell stays in there a while, even if you have the vents open. Rolling down the windows while moving gets the smell out quicker. If farts were as fatal as carbon dioxide, people would die if they didn't put those windows down. StuRat (talk) 04:27, 27 January 2015 (UTC)

When someone commits suicide in a car with CO they normally attach a tube to the exhaust pipe and poke it through a slightly open window. The exhaust gases then displace the air through the gap in the widow and any other gaps, such as the ventilation system. If the car was hermetically sealed (which would be very difficult, if not impossible to achieve) this exchange wouldn't take place and they wouldn't die. I expect the engine would probably stop too, or the tube would burst. Haemoglobin has a great affinity for CO, so a pretty low concentration will kill you fairly quickly - 0.64% will kill in about 20 minutes - see: Carbon monoxide poisoning. The flies can get into the car through the same gaps. According to our Calliphoridae article, blowfly eggs take from eight hours to a day to hatch after laying. Richerman (talk) 10:38, 27 January 2015 (UTC)

What's puzzling me about this is not the fly eggs - but the fact that someone was still able to use this method to commit suicide. Modern cars just don't produce enough CO to cause problems. For example: http://lostallhope.com/suicide-methods/carbon-monoxide-co-poisoning says:

"In the past, using car exhaust fumes to commit suicide was a well known method. Whether that was by running a car engine continuously in an enclosed space like a garage, or by running a pipe from the exhaust directly into the car, again, ideally in a garage. But that was before the days of emission controls on cars, which now emit much lower levels of CO than previously. Whilst it is possible to achieve death using this method, it does generally require older cars. The method is susceptible to a number of things that can go wrong, and for this reason it is no longer cited as an effective method of committing suicide, and certainly not in places like the US, UK and Australia where car emissions are more tightly controlled."

...which agrees with my belief that this is a TV/Movie trope that no longer holds water. I guess the incident happened "some years ago" - and we're not told in what country or what kind of car. But in general, this is really unlikely to happen at all.

Back when this DID work (maybe with cars built in the 1960's or before) it was common to simply shut the car in a garage with the engine running and all of the doors open. Victims could be anywhere in the garage - but if they chose the relative comfort of the car seat as a place to meet their end, they'd want to wind the windows all the way down. Clearly there are plenty of ways for flies to be living in a garage (eg if trash cans full of food waste are placed there)...and that makes the speed of fly infestation seem entirely plausible.

SteveBaker (talk) 15:35, 27 January 2015 (UTC)

That only holds true for cars with functioning catalytic converters. Here's some do-it-yourself removal advice. It can also die of natural causes. InedibleHulk (talk) 17:19, 27 January 2015 (UTC)

Yes, with a catalytic converter the CO level at the tailpipe is about 50% below the lethal threshold. Without a converter (i.e. if it has been disabled/removed or the exhaust is leaking out before reaching it) then the CO level is many times higher than lethal. Dragons flight (talk) 17:23, 27 January 2015 (UTC)

With normal operation, however in a closed garage the buildup of carbon dioxide displaces the oxygen available to the system, to the auto and its occupant. But it doesn't matter, because the exhaust method works regardless. In fact, a quick google of suicide and catalytic converter turned up this [1] 1998 report that the exhaust gassing method still worked: "In a sample of Coroner’s records 36% of victims’ vehicles had catalytic converters." -Modocc (talk) 18:05, 27 January 2015 (UTC)

Could be that the longer wait gives potential suicides time to ponder "Jesus Christ! What was I thinking?". Or that gradual death gives time to appreciate the lightheadedness. Giddy people are typically happier than non-giddy, and nauseous people with headaches might be conditioned to pull over and puke outside. The symptoms of monoxide poisoning aren't as bad as slowly sawing yourself crotch-first, but aren't the easiest way out, either. InedibleHulk (talk) 18:24, 27 January 2015 (UTC)

The story is behind a paywall, but the title is An interesting life': Retired Times photographer a witness to history which suggests it was some time ago. As for the flies - when something starts to decompose they are attracted to the products of decomposition and appear very quickly. I would think the adult flies must have flown in rather than hatched there as the life cycle of Calliphoridae at 20°C takes a couple of weeks and I would think the life cycle of other species would be of a similar order.Richerman (talk) 17:27, 27 January 2015 (UTC)

Carbon dioxide can also be fatal, i.e. Apollo 13 and the makeshift carbon dioxide scrubber.50.43.56.168 (talk) 20:20, 27 January 2015 (UTC)

I don't understand how people can kill themselves with car exhaust. I like a brief whiff of it in the open air on racing day, but any more than that has me running for the door. Do these people have some kind of genetic deficiency that prevents them from smelling the stink?50.43.56.168 (talk) 20:20, 27 January 2015 (UTC)

Story from high school biology class. Fly eggs may not be everywhere, but nematodes are. If everything except nematodes were to magically disappear the world would not look any different, except everything would be nematode color.50.43.56.168 (talk) 20:20, 27 January 2015 (UTC)

Did your physics class mention that gravity, transparency and translucency wouldn't allow it for long? InedibleHulk (talk) 20:45, 27 January 2015 (UTC)

Or wait, no. If all other matter vanished, like Nathan Cobb said, gravity wouldn't work. But neither would light, so it's still wrong. InedibleHulk (talk) 20:54, 27 January 2015 (UTC)