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March 13

Hand-thrown projectiles

Both cricket balls and baseball balls are quite similar in size and weight (about 5 ounces) whereas modern hand grenades can be as much as three times heavier (1 pound in the case of the M67). In the case of the balls controlability/accuracy and velocity seem to be the criteria that are emphasized, wheras hand grenades need to be light enough to throw far enough so as not to endanger the thrower but also heavy enough to be an effective weapon, a grenade with a too small explosive payload will not do worthwhile damage to the target. Accuracy is of course also an important criterion. From many news media images it seems that stones used by rioters tend to range from fist sized up to about half a brick (BTW have people who design police helmets and shields studied this topic?).

If maximum range is the main objective, is it possible to figure out in terms of human anatomy/physiology/ergonomics an optimum size/weight for a hand-thrown projectile? Roger (Dodger67) (talk) 09:21, 13 March 2016 (UTC)[reply]

There must be some literature on shot - putting and discus - throwing. Discus is an Olympic sport and maybe the other is as well. 5.150.93.133 (talk) 12:03, 13 March 2016 (UTC)[reply]

Do javelins count? The world record (before a redesign in 1986 reset the standard) would appear to be 104.8m. Rojomoke (talk) 12:18, 13 March 2016 (UTC)[reply]

Good point! When I formulated the question I quite forgot about the shape of the projectile as a factor, and of course aerodynamics is important. Are there any reliable records for distances that baseball or cricket balls have been thrown? Roger (Dodger67) (talk) 12:46, 13 March 2016 (UTC)[reply]

When I Googled the term farthest thrown baseball, it pointed me to our article at Glen Gorbous. With a six-step running start, he managed 135 m (445 feet). When I Googled the term farthest thrown cricket ball, the results point to a YouTube video claiming 132 m, so essentially the same as a baseball. When I Googled the term farthest thrown object, it pointed me to the Aerobie. If you're interested, you can perform similar searches here by using the same sort of terms as I did. Matt Deres (talk) 13:07, 13 March 2016 (UTC)[reply]

This question from last year has some useful references. The Aerobie record was beaten in 2005 with a traditional boomerang (472.2 m), but I'm not sure that such devices count as "projectiles". The 132 m figure for a cricket ball was obtained by Roald Bradstock (a javelin thrower), who claims a large number of (unofficial) distance throwing records. Tevildo (talk) 13:49, 13 March 2016 (UTC)[reply]

I'm quite surprised that the ball records are so much further than the javelin. I think we should discount objects such as the aerobie, boomerang, frisbee, etc. because they rely on aerodynamic lift and fly like aircraft, rather than a ballistic trajectory. I found a claimed golf ball throw of 170 yards, by Roald Bradstock - https://recordsetter.com/world-record/world-record-for-throwing-golf-ball/7349 -- Roger (Dodger67) (talk) 13:53, 13 March 2016 (UTC)[reply]

[1] argues that golf ball is about the best you can do for height too. Sagittarian Milky Way (talk) 21:20, 15 March 2016 (UTC)[reply]

The farthest discus throw is 74 m (81 yards),[2] so the discus is clearly far heavier than whatever the ideal weight is. --Guy Macon (talk) 20:37, 13 March 2016 (UTC)[reply]

Yes, it has been figure out in terms of human anatomy/physiology/ergonomics. See :The accuracy of throwing hand grenades. as a function of their weight, shape and size. However, this was done back in the early 1970's and considering the modern US diet, general health an life expediency is now falling behind other countries in the last 45 years, these figure may need to be readjusted down by an ounce or so.--Aspro (talk) 13:24, 13 March 2016 (UTC)[reply]

Thanks Aspro, that's an interesting article. Roger (Dodger67) (talk) 13:56, 13 March 2016 (UTC)[reply]

Don't let the creamy center of the general population fool you, though. Athletes, soldiers and regular people who just want to throw things as far as they can have much more in the way of sport science and fancy supplements (many of which are perfectly legal) than their grandparents did in the "milk, steak and barbells" day. It's just the middle class of moderately fit, moderately busy folk that's shrinking. Readjust up an ounce or so, I say. InedibleHulk (talk) 09:51, 14 March 2016 (UTC)[reply]

Note that hand-thrown objects can go faster and farther if a longer lever arm is used, in the form of an "atlatl", in the case of spears and darts, or a "cesta", in the case of a jai alai ball. A bow and arrow also uses only human muscle to propel the projectile, but differs in that the energy is put into the system when the bow is strung and pulled back, not when released. A crossbow/ballista goes even further, when a crank is used to pull it back, and a catapult/trebuchet extends the concept by using many people to pull back on the bent board or lift a counter-weight into position, to arm the device. StuRat (talk) 18:56, 13 March 2016 (UTC)[reply]

That's why the World War II era German grenades were mounted on a stick to allow the heavy end get up some decent momentum before being released. SteveBaker (talk) 03:37, 14 March 2016 (UTC)[reply]

The Islamic Penal Code of Iran gave a handy guide to the dimensions of stones to throw in lapidations: The size of the stone used in stoning shall not be too large to kill the convict by one or two throws and at the same time shall not be too small to be called a stone. AllBestFaith (talk) 19:46, 13 March 2016 (UTC)[reply]

How can a stone be "too large to kill in one or two throws", unless they mean it can't be lifted and thrown at all ? StuRat (talk) 20:15, 13 March 2016 (UTC)[reply]

I think you've misunderstood Amnesty International's? English translation of the rule. It seems clear if you take the whole paragraph that what it means is that the stone should not be too large, such that it will kill a person in one or two throws. And should not be too small such that it would not be could a stone. (Both of these are easily debatable definition at the borderline but what they are trying to say doesn't seem that hard to understand. They want a stone that is big enough such that it will be called a stone. But which is small enough such that it's unlikely to kill a person with one or two throws.) Nil Einne (talk) 20:37, 13 March 2016 (UTC)[reply]

Yes. The thinking behind Islamic Hudud stoning is that no individual executioner can be identified, rendering it impossible for the victim's heirs to demand compensation (see Diyya) or demand death of the killer (see Qisas). AllBestFaith (talk) 21:44, 13 March 2016 (UTC)[reply]

See also the scientific-sounding diffusion of responsibility. You can shoot another man all day with an imaginary bullet and no harm's done. InedibleHulk (talk) 14:59, 14 March 2016 (UTC)[reply]

Interesting question! stackexchange has a similar question. The Quixotic Potato (talk) 01:38, 14 March 2016 (UTC)[reply]

An unofficial record set in 2013 for throwing a cricket ball is 132.66 metres or 145 yards. [3] The use of a half-brick has a long and distinguished pedigree in the history of British anti-social behaviour: Who's 'i'm, Bill? - A stranger. 'Eave 'alfa brick at 'im. (PS: Apoloogies Matt, I've just seen that you posted the same cricket ball record above.) Alansplodge (talk) 11:33, 14 March 2016 (UTC

While we're on the subject, the official record for throwing a cricket ball is 140 yards 2 feet (128.6 m), set by one Robert Percival in 1882. Jānis Lūsis (another Olympic javelin thrower) has claimed an unofficial cricket-ball throw of "over 150 yards" (138 m). Tevildo (talk) 19:26, 14 March 2016 (UTC)[reply]

Did technical methods - technical levels of application and use are been determined a physical and chemical properties of all substances?

Questioner 1, RefDesk 0

The following discussion has been closed. Please do not modify it.

Did the maximum temperature of the burning – flaming of substances as also and the maximum heat capacity of substances are always been depended on the technical methods – technical levels of application and use of these substances?--83.237.192.54 (talk) 11:50, 13 March 2016 (UTC)[reply]

Did all are always been depended on the levels of complexity of technique? (Did the levels of complexity of technique are always been decided all)?--83.237.192.54 (talk) 11:50, 13 March 2016 (UTC)[reply]

How it (did) been in respect of electricity and gases in particular of natural and inert gases, if work body of any electricity did always been a electromagnetism and work body of all gases did always been a pressure?--85.141.237.179 (talk) 15:54, 13 March 2016 (UTC)[reply]

It is well known that electromagnetism of all gases including natural and inert gases is always considerably small irrespective of the valence of these gases, especially in comparison with electromagnetism of electricity, is it right?--85.141.237.179 (talk) 16:25, 13 March 2016 (UTC)[reply]

One possible reason why your questions are not being answered may be that we don't understand them. Try writing them in Russian and then machine-translating them. Robert McClenon (talk) 01:32, 14 March 2016 (UTC)[reply]

I believe that may be what they are doing. The Russian Wikipedia has a combination RefDesk/Help Desk here. I would suggest the user try asking their questions there. Matt Deres (talk) 02:26, 14 March 2016 (UTC)[reply]

In total, did a natural gases as also and all gases really always had a small technogenesis than always had electricity?--83.237.198.62 (talk) 10:26, 14 March 2016 (UTC)[reply]

I think that technogenesis always did needed for successful development, because technogenesis did society younger.--85.141.238.215 (talk) 11:33, 14 March 2016 (UTC)[reply]

As for me, I see the base problem of gases technogenesis is that, did a gas generation of electromagnetism had a perspective, if it's electromagnetism did not had been much as good?--83.237.218.90 (talk) 15:29, 14 March 2016 (UTC)[reply]

Is been good idea to microwave this. InedibleHulk (talk) 15:41, 14 March 2016 (UTC)[reply]

It looks, what is safer or use safer a gas or electromagnetism?--83.237.218.90 (talk) 16:10, 14 March 2016 (UTC)[reply]

Did technical methods - technical levels are always been guaranteed a safety?--83.237.218.90 (talk) 17:36, 14 March 2016 (UTC)[reply]

What is meaning the levels of complexity of technique?--83.237.218.90 (talk) 18:33, 14 March 2016 (UTC)[reply]

Those are all excellent questions. InedibleHulk (talk) 22:28, 14 March 2016 (UTC)[reply]

We shouldn't be in the business of driving enquirers away from the reference desk. Ours may be much more authoritative, in the same way that a central reference library may be more informative than a branch library. A suggestion was made for resolving this problem:

Hi. You're calling from Russia. Would you like to say what you want in Russian, and one of our administrators, Yaroslav Blanter (Ymblanter) may be able to deal with this. 212.159.171.206 (talk) 16:52, 17 February 2016 (UTC)[reply]

Distance updates due to expansion of the Universe

Due to constant changes in galaxies' distances from Earth amid Universe's expansion and redshift, is it neccessary to specify the date of measurement each time it's mentioned? Something like "1 billion light years from Earth as of March 13, 2016". Why academic sources don't specify that and do not seem to update the distances? Thanks. 93.174.25.12 (talk) 19:21, 13 March 2016 (UTC)[reply]

The rate of expansion of the Universe is estimated to be between 60 and 80 (km/s)/Mpc and does not add significantly to the error in recent distance estimates. The value of the Hubble constant is estimated by measuring the redshift of distant galaxies and then determining the distances to the same galaxies (by some other method than Hubble's law). AllBestFaith (talk) 20:03, 13 March 2016 (UTC)[reply]

Agreed. It would be a bit like saying the distance from New York City to London varies with the date, due to plate tectonics. It does, of course, but the amount is insignificant unless you look at it over very long time frames, like millions of years. StuRat (talk) 20:13, 13 March 2016 (UTC)[reply]

I am reminded of the joke that goes along the lines of: a janitor at a museum is told a dinosaur fossil is 100 million years old, and a week later he excitedly tells visitors that the fossil is 100 million years and a week old. --71.119.131.184 (talk) 23:44, 13 March 2016 (UTC)[reply]

That's a lot like the old joke where a teacher is telling children visiting an observatory that the temperature at the heart of the sun is "millions of degrees"...but forgets whether that's centigrade or fahrenheit. A crusty old physics professor who's listening at the back clears his throat loudly and says "Kelvin". SteveBaker (talk) 03:31, 14 March 2016 (UTC)[reply]

In different units, the Hubble constant is about 0.00007 Myr⁻¹. That is, the universe is currently expanding by about 0.007% per million years, or 0.000000007% per year. -- BenRG (talk) 20:34, 14 March 2016 (UTC)[reply]

Would it be possible to have a SEM at home?

Ok, just because I'm curious. Would it be possible to have a scanning electronic microscope at home (regardless of price and space)? I think there would be some problems due to electric energy consumption and/or preparation of specimens.--Carnby (talk) 20:31, 13 March 2016 (UTC)[reply]

I took a glance at a few SEM manuals, and they seem to take normal house phase/voltage at a few tens of amps. DMacks (talk) 20:56, 13 March 2016 (UTC)[reply]

See the article Scanning electron microscope. The equipment is advanced for a home installation since it includes a vacuum chamber, high voltage supplies and a dedicated display. Biological specimens that are non-conductive usually need to be prepared with a conductive coating, e.g. of sputter coated metal. This video explains the basics. AllBestFaith (talk) 21:29, 13 March 2016 (UTC)[reply]

If your pockets are deep enough, sure, you should be able to use a SEM at home. If DMacks is right, power shouldn't be a problem, and even if it is, I'm sure it would be possible to buy an external generator.

As for specimens, that really depends on what you want to look at. If it's conductive, then you can look at it easily. If not, then it's trickier. Poorly conductive samples can be looked at briefly, but will quickly charge up and become invisible. Sputtering generally requires some serious equipment, so sputter-coating may be difficult to do at home. Then again, a quick search reveals that people have actually made sputtering machines at home, so I guess even that is not out of the question.

In any case, you'll generally want to put a SEM in a very clean environment. If you have a spare room to put it in, you should consider installing additional air filtering and adopting basic cleanroom protocols (a gray room to put on a cleanroom suit already goes a long way), though you that's not really a requirement. Whatever you do, always wear fresh disposable gloves when interacting with the sample chamber. I had to use a SEM that wasn't located in a cleanroom, and one of the big issues was carbon deposition. Any number of sources can contaminate your sample chamber with carbon, and it will get attracted to the areas of the sample you're looking at (especially at high beam intensities/high magnification). It's really annoying to see your sample turn black in a matter of seconds! You can mitigate that to some extent by keeping everything really clean.

Another major problem you might face in a home setting is vibration. That's no biggie at low magnifications, but if you want to image structures of tens of nanometres, it'll ruin your day. If possible, try to have some separation between your SEM and its vacuum system; the pumps introduce a lot of vibration. If you live near a busy road, vibrations from traffic may even be a problem. --Link ^(t•c•m) 21:53, 13 March 2016 (UTC)[reply]

Would think that a industrial SEM would draw most current when pulling a vacuum – in order to reduce the waiting time. After that, a few hundred watts should be sufficient. I'm normally weary of thing that I see on Youtube but this feller claims to have built one. [ https://www.youtube.com/watch?v=VdjYVF4a6iU DIY Scanning Electron Microscope] At first I was doubtful that he could pull the necessary vacuum inside a bell jar but he goes onto explain he uses both a mechanical and diffusion pump. His apparatus looks clean (no sign of organic oils). For something like this one would need to thoroughly degrease and then depend upon silicon grease only. His solder joint appear clean of flux (any oversight like this can slow down degassing and pulling a hard vacuum). His electronic units are also housed in nice 19 inch racks. So in this case, I think he has indeed built a home SEM. As to your second question about preparing specimens. Inorganic materials etc., may not cause a problem but biological specimens can create all sorts of challenges. Yet, for any one with the know how to build a working home SEM, it should not be beyond their skill to use the same basic set up for physical vapor deposition. As for clean room - I'll send my wife around. Vibrations... 2 to 4 am is a vibration free time. - Don't know, what the current price for SEM images are today, but if one costs ones free time at xx dollars per hour, a lab may be able to do the job more cheaply than messing about building ones own – but hey – to have ones own SEM must be very satisfying. So in answer to your question: It is possible to have a scanning electronic microscope at home.--Aspro (talk) 22:26, 13 March 2016 (UTC)[reply]

Despite the extraordinary spending that often goes into them (largely due to pork barrel politics by HVAC manufacturers I think) there's nothing that exceptional about laboratories as buildings. They have regular outlets with the same 110 or (rarely) 220 volt plugs as you can have in your house. Sure, they have solid concrete floors but the same can be found in many basements. Given that the question assumes someone can afford SEM equipment, I don't see why he couldn't set it up in a home. Wnt (talk) 15:26, 14 March 2016 (UTC)[reply]

Does woman can have an erection in her clitoris if she looked in men?

Does woman can have an erection in her clitoris if she looked in porn (without touching there), like what happens sometimes to men who watch porn? 93.126.95.68 (talk) 23:51, 13 March 2016 (UTC)[reply]

See Clitoral erection. Tevildo (talk) 23:54, 13 March 2016 (UTC)[reply]

When watching heterosexual erotic videos (ref), men may be more likely than women to objectify the opposite-sex actor. There are reported differences in brain activation to graphic sexual stimuli, with men showing higher levels of amygdala and hypothalamic responses than women. AllBestFaith (talk) 00:58, 14 March 2016 (UTC)[reply]

According to 2013 research conducted at McGill University, both men and women become sexually aroused at similar rates when viewing sexually explicit videos. Cullen³²⁸ Let's discuss it 01:12, 14 March 2016 (UTC)[reply]

Careful. Calling the Gender Gap a Myth is practically bannable. --DHeyward (talk) 15:47, 14 March 2016 (UTC)[reply]

"Objectification" is not a scientific concept. To figure out what actual science was meant by it, I looked at the source, "Sex Differences in Response to Visual Sexual Stimuli: A Review" by Rupp and Wallen. To my surprise/horror, the word is used there too. Here's one example: "Women's ability to imagine themselves as the woman in the film was the only factor the [sic] strongly correlated with their reported arousal. Men, however, rated the attractiveness of the female actor and the ability to observe the woman important in their arousal to the film in addition to imagining themselves in the situation. These results suggest that although both men and women project themselves into the scenario, men may be more likely to objectify the actors within the stimuli." So apparently if you're interested in the opposite-sex actor you're objectifying them, and if you don't care about them that's fine. I bet that if the data had gone the other way, they would have argued that by identifying with the same-sex actor and not caring about the opposite-sex actor, the men reduced her to an object for their own enjoyment. Because everyone knows men objectify women, so that must be what the science says.

This shouldn't be in Wikipedia (or in a peer-reviewed journal, but at least Wikipedia is potentially fixable). I don't know whether to delete the reference and everything copied from it, or just replace "objectify" with the science behind it. Is the whole section based on bad research that should be replaced by the McGill study? Can someone who knows more about this subject do something? -- BenRG (talk) 18:35, 14 March 2016 (UTC)[reply]