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How many different supernovae contributed the carbon on Earth?
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There's a problem here with the initial question: interstellar carbon doesn't just come from supernovae. A very substantial percentage is produced from the mass loss of [asymptotic giant branch stars](_URL_0_). Stars as small as half the mass of our Sun will undergo this phase near the end of their lives. Through a series of helium "flashes", where helium fusion initiates and then is later damped out, carbon that would normally be limited to areas near the core gets thoroughly mixed throughout the star. Combine that with strong stellar wind streaming off the surface of these stars (they can lose half their mass in the process), and you've suddenly got dying stars all over the galaxy seeding carbon into the interstellar environment. This generally takes the form of fine dust particles similar to soot. As a result, just about any giant molecular cloud in our galaxy will have been seeded with carbon from a very large number of non-supernovae stars.
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Why does fire travel upwards?
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Because things expand when they get hot, and expanded gas is lighter than not-expanded gas (because the same mass takes up more volume).
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Why is my reflection right-side up in the bottom of a spoon but upside-down in the top of a spoon?
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Basically, the inside of a spoon is a concave mirror and focuses the light inward such that the beams cross and the image appears inverted. A convex mirror (outside of spoon) reflects the beams outward. I draw picture: _URL_0_
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Why is your reflection in a spoon upside down?
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First thing you need to understand about images in a mirror is that there are two types of images - virtual and real. A virtual image is formed behind the mirror and is always upright. It is formed by tracing the path of light backwards as shown here _URL_0_ A real image is formed when rays if light actually intersect as shown here _URL_1_ Note that Cis the center of curvature of the mirror surface and F is the focal point whuch lies exactly in between C and the mirror. If the object is between F and the mirror, the image is virtual and erect and if it is beyond F, the image is real and inverted. Now coming to the spoon, the focal length is quite small (approx 1.5 - 2 cm) and thus you (the object) is usually always beyond the focal point and hence the image is always real and inverted. If you jold the spoon too close to you, the image turns virtual and quite magnified and usually you cannot quite make out what you are seeing. Hope this helps. Feel free to ask if you need further clarification
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Do we really not know what causes hiccups? Or does everyone just think that because that's what we've been told since kindergarten?
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_URL_0_ This pretty well explains hiccups in a quick and easy to understand way. Google is great. Hope this helps.
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When we watch videos on YouTube do they get temporarily stored on the hard-disk or phone's storage or are they just stored in the RAM for some time ?
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In an OS with virtual memory, any virtual memory unit (most commonly, a _page_) may at some point be stored on disk - or more accurately, not in main memory. The process of moving a page to "secondary" storage is called _swapping_. [This](_URL_0_) is a good overview of how the concepts around virtual memory work.
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What actually happens if you put wrong gasoline in a car (diesel instead of regular)?
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Putting diesel in a gasoline gar is relatively harmless, as diesel requires higher pressures to ignite that gasoline and your regular engine won't start at all. The other way round is dangerous though. The diesel engine tries to compress the fuel air mixture a lot, but the gasoline explodes prematurely. This damages the cylinders.
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If all galaxies are expanding outwards, does that mean we are actually moving at thousands of miles per second? Does that mean if you revisit your old house 30 years later, it is the 'same place' relative to Earth, but really it is in a vastly different location in the grand scheme of the universe?
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There is no single reference point. You can choose to consider yourself stationary or moving at great speed, it is all the same.
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Why do we vocalize the sensation of pain?
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I don't know about pain specifically (so sorry if this qualifies as layman speculation), but I know crying is often explained as a way of signalling to others that you are distressed, so pain could be similar. Screaming when you get injured draws the attention of people nearby to come and help you.
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What is the difference (if any) between looking at the solar eclipse and just looking at the sun?
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I don't believe it's an issue of solar eclipses being extra damaging, but rather an issue of people wanting to look at it. The sun is very bright normally, and burns our eyes when we look at it. This prevents us from looking at it. Whereas during a solar eclipse, our eyes don't burn, and we're able to view the strange phenomenon, unknowingly damaging our eyes in the process. I'm not sure what the light difference is, but hopefully I explained why so many people use goggles and what not.
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Would changing the mass of a planet affect its orbit?
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It would not affect the orbit. Assuming the mass was added without large impacts against the planet, and also not by having the mass moved towards the plabet from outside - like a huge asteroid being dragged to the surface.
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Is it possible that there are other elements on other planets that we have none of here on Earth?
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No. If you're asking about elements, no. If you're asking about compounds, yes. Elements are stable up to 92 protons, thats uranium, and the further up you go the more unstable it becomes and the element decays. Radioactive-decays. Its a foundation of ours physical understanding that nucleus of elements decay when becoming too heavy. So you wont find on some other planets elements with 214 protons for example.
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If there are parts of the universe so distant that their light has not yet reached Earth, how often do objects suddenly 'appear' to astronomers?
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They don't. At least not anymore. Due to the accelerating expansion of space, the outer edge of the observabe universe is expanding away from us faster than the speed of light. Therefore, any light emitted from these objects will never reach earth. Think of an ant walking on a rubber band. The rubber band is getting longer at a rate that is faster than the ant can walk. It will never reach the other side.
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Can non-carbon based lifeforms exist?
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We do not know and have never observed such life. Chemically, carbon is incredibly versatile in ways that other atoms simply cannot compare such as forming long chains and branches with itself (and other atoms like nitrogen) in complex shapes. While nature is generally more creative and subtle than we are, it doesn't look very likely.
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Why is helium used for creating extremely low temperatures?
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Helium is simply the coldest inert gas in its liquid form, at 4.2 kelvin. So we simply compress it into liquid form and bam we have a 4.2k environment. From there you can us adiabatic cooling and dilution techniques to reach millikelvins. Its the only liquid that will do this and do so safely. Look up helium dilution refrigerator. On the contrary a dewar full of liquid hydrogen is pretty much a bomb and we can't have those sitting around university hallways. Also I don't think liquid hydrogen is as cold.
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Is there any REAL difference in retention between audiobooks and hardcopy books?
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I found this: _URL_0_ > Results showed that reading aloud led to the least amount of mind wandering, while listening to the passage led to the most mind wandering. Listening to the passage was also associated with the poorest memory performance and the least interest in the material. It probably does vary with audio v. visual learner and attention span. I personally love audiobooks and being read to, but I don't retain or experience them the same or as well as when seeing the text.
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What causes some nebulae to form such distinct shapes?
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Nebulae shapes can hugely depend on the stellar populations therein. Stars can shape the ISM (interstellar medium) in the form of radiation pressure, which can act like a snow plow in dredging up surrounding material. Probably more commonly in these dense nebulae is the effect of newborn stars: when a star is first formed in a molecular cloud, in order to conserve angular momentum, they will often eject mass in the form of binary outflows, which can shift material around. Whether or not the nebulae is a "hole" depends on the picture and the nature of the image. The horsehead nebulae is dark because the dust there is cold and dense, opaque to optical light. [Look at it in other wavelengths](_URL_1_), however, and the picture is sure to change :) [The Eagle Nebula](_URL_0_) is another example of this.
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Is it possible that there was more than one big bang?
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The universe is not expected to collapse. For reasons that are poorly understood at this time, the expansion of the universe is [accelerating](_URL_6_). This is a mostly-accepted but very puzzling fact of cosmology. If you have any [unsubstantiated guesses](_URL_4_) as to why the expansion of the universe should keep accelerating, you will be on an equal playing field with the experts. Anyways, there will never be a "big crunch" or anything. The universe will simply continue to expand forever, and possibly [rip itself apart](_URL_5_). Cyclical universes are philosophically appealing and [not completely silly](_URL_6_) but our universe could be unique. Or not.
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Does the temperature of food increase linearly in a microwave?
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Not in general. As an example: Ice doesn't absorb microwaves well. If you heat a block of ice, it gets warmer, but not that fast - meanwhile you heat up the rest of the microwave. Once you reach 0 degrees it starts melting, the water absorbs more power, but now all the heat is used to melt more ice - the temperature stays constant until all ice is molten. Afterwards you have water, which absorbs microwaves very well, and gets warm quickly. If you have frozen food that is not a soup, water and ice cannot mix easily, and you get a problem: Some parts will absorb more power, melt earlier, and then absorb even more power. You end up with some hot regions and some regions that are still frozen. For that reason frozen things should be heated up slower (giving the heat time to distribute in the food), or stirred in between.
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Could an asteroid be big enough to do any kind of damage to the sun?
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No. Asteroids are, per definitions pretty much, small. Asteroids (or at least icy ones) can't be larger than Ceres (950km diameter). Otherwise they would be (dwarf) planets. The Sun wouldn't even notice being impacted by such a body. Even a large object, like the Earth, wouldn't be able to damage the Sun. It would be able to affect its rotation and maybe cause a huge explosion (depending on how it impacts), but it wouldn't be able to do much permanent damage.
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Is there an evolutionary reason as to why nipples become erect when exposed to cold temperatures?
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two fish is asking why, (evolutionarily) not how. this [is and explanation](_URL_0_) which boils down to we do not know.
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Why are there only 3 generations of quarks?
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Probably not and we don't know why there is more than one generation. > Fourth and further generations are considered to be unlikely. Some of the arguments against the possibility of a fourth generation are based on the subtle modifications of precision electroweak observables that extra generations would induce; such modifications are strongly disfavored by measurements. Furthermore, a fourth generation with a "light" neutrino (one with a mass less than about 45 GeV/c^2) has been ruled out by measurements of the widths of the Z boson at CERN's Large Electron–Positron Collider (LEP). Nonetheless, searches at high-energy colliders for particles from a fourth generation continue, but as yet no evidence has been observed. In such searches, fourth-generation particles are denoted by the same symbols as third-generation ones with an added prime (e.g. b′ and t′).
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Change in enthalpy for transition of carbon in the diamond form to carbon in the graphite form is apparently a negative number (-453.5 cal). According to this, graphite is more stable than diamond, how’s that possible? Isn’t diamond supposed to be stronger and more stable than any other material?
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At standard conditions (1 atmosphere, 20 degrees celsius), graphite is a more stable form of carbon than diamond. However, the energy barrier to cross means that spontaneous reordering of diamond into graphite is essentially negligible. This doesn't affect the hardness or other physical properties of the material. Indeed, an even less stable form of diamond, called [lonsdaleite](_URL_0_), is predicted to be even harder than standard (cubic) diamond.
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What is a "flat universe"?
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A flat universe is an universe that at large scales has zero spatial curvature. It doesn't mean that the universe is two-dimensional, but rather that its geometry is Euclidean: parallel lines don't cross, the Pythagorean theorem works, and the sum of the angles of a triangle is 180º.
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Do babies begin to speak at the same age regardless of language?
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Yes. See Eve Clark's *First Language Acquisition* for a comprehensive overview.
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I've noticed that Asians tend to have more manageable hair than Caucasians. Is there any explanation or is just hygiene habits or something?
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Its a genetic. The difference comes from two factors. First comes follicle shape. The actual growth has to do with the shape of the hair follicles. Straight haired people have straight follicles that have a circular opening. People with curly hair on the other hand have curved hair follicles with a tight oval opening. The second cause is from hair composition. Hair is made of protein and this protein is made up of sulfer atoms. In people with curly hair there are many sulfer bonds throughout the hair. On people without curly hair there are much fewer sulfer bonds. The reason why each race has different hair characteristics is each race has different genetic traits. According to these rules Asians would have very circular follicles with very few sulfer bonds while Africans have very curves follicles with many sulfer bonds. These bonds however can be weakened through chemicals. (hair straighteners weaken the bonds in the hair which makes hair straight)
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Why do caucasians have so much greater variety in hair color and hair straightness/curliness compared to every other race?
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Partly because the "race" concept is highly arbitrary. The word Caucasian is a blanket term that carries very little science in it.
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Why are so many archaeological finds buried?
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Everything that isn't buried was found long ago.
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Why are so many human artifacts “buried”?
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If it was left on the surface there's a much lower chance of it surviving hundreds and thousands of years.
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What is happening to my brain during a fever dream
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When you have a high fever, enzymatic action all over your body begins to slow or fail all-together (this is a reason why people die from hyperthermia; enzymes fail to function at high temperatures). In the brain, this causes an unbalanced level of certain neurotransmitters and other psychoactive compounds due to the lack of enzyme function needed to break down or create them. When this occurs, hallucinations, 'stroke' (due to heat), and other odd feelings begin to surface. Eventually, if the fever continues to rise, delirium, loss of consciousness, coma, or death can occur. Edit: Best I can do for a source is an abstract and to hope your prior knowledge is the same as mine. _URL_0_
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Can LED light ever look as natural as incandescent light bulbs?
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Yes, it is possible -- we can generate every frequency (pure black being an exemption) to a few decimal places of precision now with LED and laser diodes by merging and diffusing different colors, but the main issue that we have encountered is being able to get the same brightness levels with properly merged colors without an insane amount of additional cost, size and heat. Eventually it will happen, the economics just don't work out right now.
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What causes an itch?
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This article from The New Yorker is a fascinating, if not mildly horrifying in places, read about the way the brain puts together our perception of itch, and what happens when the system goes wrong. _URL_0_
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What affect does drinking alcohol have on a person taking prescribed antibiotics?
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[A doctor from the Mayo Clinic answers your question.](_URL_0_)
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Why does our stomach 'growl' when we become hungry?
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[Why does my stomach growl?](_URL_0_) from How Stuff Works.
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Why does your stomach growl when you are hungry?
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The growl of your stomach is called borborygmus. It is caused by the flow of the gases in your small intestine induced by contractions of your digestive sistem. The reason that you can only hear it when you are hungry is because your intestine has a bigger amount of gases (or less food).
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Is prolonged sun exposure actually associated with LOWER RISK OF / BETTER OUTCOME FOR SKIN CANCERS? Or even just for MELANOMA only?
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Can we DELETE THIS and MAKE the title LESS SENSATIONAL?
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Can a single celled organism get cancer?
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No. "Cancer cells are defined by two heritable properties: they and their progeny (1) proliferate in defiance of the normal constraints and (2) invade and colonize territories normally reserved for other cells." (Essential Cell Biology, Garland Science, 2010) A single-celled organism thus can't get cancer because they're only "responsible" for their own survival, and not their neighbors or the community of cells as a whole.
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If my iPhone is connected to a Bluetooth speaker, does the volume level on the iPhone impact the amount of power being consumed by the iPhone?
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No. Your iPhone is transmitting data packets to the speaker over-the-air to set the output level. The data packets controlling desired volume do not use more energy when they encode "65% max output" instead of "25% max output".
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On stealth aircraft, how is it possible, that radars can 'see' out of the airframe, but enemy radars cannot see in?
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Stealth does not mean radar cannot see it. The shape of the aircraft or item uses the inherit flaws of radar to mask itself. Radar works by waves being emitted, hitting and object, and returning to the receiver. If the waves bounce off at a different angle, say away from the receiver, then the object is not seen. Also some materials used int he design absorb radio frequencies thus diminishing the return echo. Radar leaving the aircraft is fine since the geometry of the transmitter and receiver are included in the initial design. Couple this with shrouding your engines exhaust and reducing your glare from the sun and you can make the aircraft "undetectable" until it is too late.
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Is there a maximum temperature my microwave oven can heat something up to?
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Yes, although it is very, very hot. The heat an object loses is proportional to it's surface area and the difference in temperature between it and it's surroundings. Bigger object loses heat faster than a smaller object, hotter object loses heat faster than a warm object. So, at some point your object in the microwave will be losing more than the 1,000W you are putting in. Assuming it doesn't dry out first. Or catch fire and destroy your microwave.
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Is there a maximum temperature a microwave oven can heat up a piece of food?
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[Grape plasma!](_URL_0_) Heat common produce until it glows like an arc welder! Grapes are mildly electrically conductive and their size is close to the wavelength of the microwave. Induced current moving back and forth over the narrow connection between the halves of the split grape drives it to enormous temperatures. Plasma is also conductive so the oven continues to drive fucktons of current through it keeping it twisting around in there at several thousand degrees. Caution, vaporized organic matter has a unique smell and may cause your microwave oven to melt or make the glass parts shatter.
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What variables determine the price of a stock?
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A stock is worth whatever somebody is willing to pay for it, at a particular moment. If I'm selling, and asking $20, and somebody's willing to buy it for that price, that stock is worth $20. Its a balancing act of sellers trying to ask as little as possible to undercut each other, while still making a profit, and buyers trying to spend as little as possible, but maybe bidding high if they think a particular stock might be valuable. So what you end up with is a situation where in the short-term, you get a bunch of sales randomly scattered around a certain value, but over long periods of time, the average value those sales are centered around can move, either due to the company issuing the stock becoming better or worse in some way, or because stock brokers *think* it is.
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How is a stock's price determined?
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The price that you see changing in real time is just the price of the last transaction that takes place at the exchange. As for how the price is determined, there is this thing called an "order book." When you want to buy some shares, you'll make a bid: I'm willing to buy this many shares at this price point. That bid, along with bids from other people, goes into the order book. At the same time, someone who wants to sell their shares will make an offer (also called an ask): I'm willing to sell this many shares at this price point. That also goes into the order book. If the exchange finds a bid and an offer whose prices match, a transaction occurs. That price becomes the reported stock price. If you want to buy some stocks but you don't care about the price, you don't have to make manual bids. The exchange can just match you with the cheapest available offers in the order book. This is called a market order.
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If Bill Gates and Warren Buffett gave $15B to astronomers and said, "build the most amazing telescope you can", what would the specs be and what could we see?
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The price tag of the James Webb Space Telescope project is estimated at about half of that (estimated 8.7B in 2011). This will be a successor to Hubble, and will mostly see in the infrared looking for information about the formation of galaxies and stars/planets.
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What is our solar systems orientation as we travel around the Milky Way? Are other solar systems the same?
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To answer the second observation-- the north star just just coincidentally our north star. Even now, it is not perfectly aligned to our axis of rotation, and will continue to deviate as the centuries whiz by. In some thousands of years a different star will take it's place as our most northern-est star.
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Why do some people think using an inner monologue and others simply "think"? What's the difference? Is one more advantageous than the other?
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I actually had no idea everyone didn't use an inner monologue. TIL.
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Is there a reason for why we sound out an internal monologue in our minds, rather than just "thinking"?
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Not sure why that is, but you may find this [RadioLab episode](_URL_0_) interesting. The first part is about a guy that never learned language until much later in life and how he thought before he had language is mentioned a bit.
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If an ant was the size of a human, would it still be able to lift 10x it’s body weight?
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No. This is commonly referred to as the "square-cube law". Basically, the strength of something relates to its cross-sectional area - how thick it is. If you scale up something by a factor of 2, then the cross-sectional area of the arms/legs/etc increases by a factor of 4, i.e. the square of the scale factor. However, the *weight* of something increases with its *volume*. This increases as the *cube* of the scale factor. So if you double the scale, your object now weights 8 times as much. In practice, what this means is that small things can support themselves with very thin spindly legs, while large things need very solid legs directly underneath them. If you want to scale up an ant to human size, you can't keep its legs in proportion, or else it will just collapse. You need to make its legs much bigger, and more directly under its body, or else it won't even support its own weight.
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Rubbing alcohol... cool to the touch?
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alcohol evaporates which pulls uses energy, leaving less heat on the area it evap'd from. this makes it feel cool (ianascientist)
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Is it possible to see so far into space, you can see the big bang?
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Here is my understanding. Right right after the big bang, the universe was overall an electrically conductive material. EM waves can not propagate very far in a conductive material, so there is no remaining radiation from that immediate time. It couldn't "propagate" A little while later, matter starts forming hydrogen, and the universe becomes transparent, allowing radiation to propagate. We can see the radiation that existed at the point of time in the universe by looking "far enough". It is known as the [cosmic microwave background](_URL_0_) . My understanding is the universe was [~400,000 years old](_URL_0_#Features) when it happened. So out of the 13.798±0.037 billion years of the universe, we can pretty much see all the way up to 13.798 10^9 - 400,000 ~ 13.797 10^9 years...so pretty far back.
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Have we estimated an average number of planets orbiting a star?
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That is very, very hard. The problem is the two best methods we have are very biased in what they can see. Most of the first extrasolar planets we found by the radial velocity method method, which depends on the planets being massive and orbiting with periods ~ a few years or less. The other method, employed be the (freaking AWESOME) Kepler satellite, has a bias towards planets very close to their hosts (a system with 6 planets inside the orbit of mercury was discovered, to give you a sense). So we really have very little sense of the number of planets at the distance Jupiter is from our sun, for instance. There is a method that is largely unbiased, microlensing, but it is pretty hard to do, given the low mass of planets. Some have argued that there are many free-floating planets from this method, but that is rather uncertain. Still early days, but I'd guess our best chance to answer your question will come from very high-powered microlensing surveys.
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How are Guide (seeing eye) dogs trained?
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I dated a girl who was really into training these dogs. Basically, they spend the first couple years of their lives living with people who are trained to start these dogs out right. The dogs live with them, but must abide by strict rules. They learn basic obedience in these homes and are taken out into the world as if the owner was blind. Everywhere we went, every date, every errand, the dog was with us. After they reach a certain age (determined by the school), the dogs are turned over to the professionals who do intensive training for about 6 months. By the time the dog gets here it should be very comfortable in public places around lots of strangers and have very strong obedience skills. Not all dogs are successful at being trained, if they are not well suited for the job, the previous trainers have the option of keeping the dog, or it goes up for adoption.
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When filling up a water bottle, why does the sound get higher pitched as you fill it up?
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Because the wavelength of sound that resonates in the bottle is getting shorter. Basically, it's like sliding your finger up a guitar neck. As you shorten the string, the wavelength gets shorter, but the speed of sound in the medium (the guitar string) stays the same, so the frequency goes up. The water bottle is the same, except instead of using a string as an oscillator you're using the air in the bottle.
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Exactly how do colds (a virus) cause secondary bacterial ear infections?
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1) your immune system is already compromised, so it’s easier to get secondary infections 2) the congestion and inflammation symptoms of your cold interfere with the ability of your sinuses and Eustachian tubes to keep mucus flowing, turning your sinuses and inner ear into little Petri dishes 3) the bacteria is already there; normally kept in check by being flushed out, eaten by your immune system. 4) small children have smaller Eustachian tubes that clog easier. (Edited to add 3+4)
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What am I hearing when I close my eyes and flex the muscles responsible for blinking?
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It's activation of the tensor tympani muscle, also activated when you yawn. Check out [r/earrumblersassemble](_URL_0_) for more info.
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Why are bullets rounded instead of being sharp (like a bullet-arrow)?
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I think that the idea behind round lead bullets is that upon impact they deform and spread out, causing a bigger hole and thus more damage to whatever it is you're shooting. If the bullet was pointy, it might not deform as much.
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/r/askscience, does the Earth and Neptune orbit the sun at the same speed?
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No, Neptune has an orbital velocity lower than that of earth (29.78 km/s vs. 5.43 km/s). Neptune travels slower as the Sun's gravitational attraction is less at that distance. If it traveled the same speed as earth, it wouldn't accelerate fast enough due to the Sun's gravitational force to maintain its orbit and it would fly outwards.
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What makes hair grow curly or straight?
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[This link](_URL_0_) has an excellent write-up about it. In short, your genetics determine follicle shape and the amount of cross-linking in your hair. The rounder your follicles and the less sulfur bridges you have in your keratins, the straighter your hair will be.
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"Sharks can smell blood from up to 5 km away"...how?
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It's all about the ability to detect certain chemicals in solution. Normally, you (as a human) will detect certain volatile molecules carried in the air - those molecules could be given off by baked bread, a flower, a fart. In the ocean, it's just the same - only those molecules will be in solution or suspension in the water. If a shark can detect blood from 5 km away, it's because the ocean currents have carried those same molecules of blood for 5 km. It's probably more accurate to say that a shark could detect a miniscule amount of blood in an Olympic-size swimming pool (the universal measurement of volume).
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Are there tornadoes anywhere other than in North America?
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Tornadoes occur in [many places](_URL_0_), but about 75% of them occur in the US. The US also gets more powerful tornadoes overall, and they tend to hit places where people live, so you hear about them more.
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When you open the microwave, why isn't it hot inside after cooking for a while?
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microwaves heat the water molecules inside the food, as opposed to ovens that heat the air which heats the food.
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Is the sun soft or hard?
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So I found a [website](_URL_5_?) which talks about the sun having a solid surface beneath the photosphere described as a "hard and rigid ferrite surface", which goes against other models of the sun so far. Anyone have any further knowledge about this? Is this speculation or is there hard supporting evidence?
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Why don't Pluto and Neptune ever collide despite crossing orbits?
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I thought this was interesting but figured that the most logical answer is that "space is really big" and that the orbits don't actually intersect (different planes, etc.) - they only appear to from specific perspectives. This older reddit thread backs that up. You might find it interesting: _URL_0_
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If I leave ice cubes in the freezer (refrigerator) long enough they eventually shrink, why?
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A phenomenon called sublimation. Ice is just a group of water molecules that are very ordered (in a crystalline structure). Just like liquid water, occasionally the motion of the molecules causes/allows one to "escape" into the air. It just happens much less often because of the more ordered structure and smaller amount of motion of the molecules in the solid ice...
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With planets like Jupiter that have multiple moons, do the moons ever collide? Or is there something in the way they orbit that keeps this from happening?
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When you have multiple moons, this is the notorious n-body problem (more generalized than the 3-body problem). You can't solve these problems exactly, so you can never truly rule out a collision in the distant future. There is even a possibility that Mercury or Venus might crash into Earth. (That is billions of years away, so nothing to lose sleep over!) That being said, the three inner Galilean satellites (Io, Europa and Ganymede) are in a 4:2:1 orbital resonance. Meaning Io orbits 4 times for every 2 orbits of Europa and 1 orbit of Ganymede. This resonance helps the moons to be self correcting in their orbits. They will be gravitationally nudged back to a stable state. However the other moons in the Jupiter system we can't say the same thing and possibly in the future they may collide. Also orbital resonance can be destabilizing, but after billions of years, those objects have mostly been kicked out. There are some subtleties, so I'll let you read the following. _URL_0_
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If dogs evolved from wolves, did cats evolve from panther like creatures or have they stayed relatively the same for the past few thousand years?
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More likely the opposite. All cats evolved from a proto-felid animal that would have looked a lot like a [viverrid](_URL_0_) of some sort. It was relatively recent, only about 10-15 million years ago. A lot of detail is found [here](_URL_1_) From this point cats evolved into multiple branches. Some became larger and became Panthera (lions, tigers, leopards, jaguars). Other stayed small and became African wildcat, European wildcat, jungle cat, and Chinese mountain cats. This happened 6-7 million years ago. Exactly what happened from here is debatable. Every few years a study seems to show that the domestic cat came from one or another of these lines. African and Northern European strains seem to have the most credence. The fact is all of these cats are closely related and can interbreed easily, so its very possible there were multiple domestication events of different wildcats.
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If dogs evolved from wolves, what did cats evolve from?
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From _URL_0_ > Genetic, morphological and archaeological evidence suggests that the housecat was domesticated from the African wildcat, probably 9,000-10,000 years ago in the Fertile Crescent region of the Near East, coincident with the rise of agriculture and the need to protect harvests stored in granaries from rodents.[3]
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Can Helium be in a solid state?
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Here are [the phase diagrams for both isotopes](_URL_0_), ^3 He and ^4 He. For temperature below around 1.5 K, ^4 He will solidify at pressures above about 25 MPa. In the case of ^3 He, there is a minimum in the melting curve at a pressure of ~ 2.9 MPa and a temperature of 3.16 K. Both are generally considered to be 'quantum solids' since zero-point vibrational energies are large compared to the thermal energies at the melting points. The two isotopes differ due to their different nuclear spins, and are consequently governed by different quantum statistics.
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Is my occasionally excessive earwax production a reaction to protect my hearing?
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Studying Hearing Instrument Specialist here. Your ears do have a protective function for loud noises but it has nothing to do with ear wax production. Some people just produce more than others, I am one of those people. I tend to have to get my ears cleaned once or twice a year or they inevitably plug. You should know though that if you are listening to headphones louder than recommended you absolutely are doing permanent damage to your ears. People disregard hearing because it's not as understood as the eyes. You know not to look into the sun but don't realize that blaring headphones is basically the equivalent for the ears. EDIT: Sorry I forgot to explain the reasoning for ear wax. It's to repel insects. Without it a small, dark, warm cavern would be an ideal nesting area for bugs.
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Would two stars last longer if they crashed into each other?
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The bigger a star is, the faster it uses up its fuel. So a star with half the mass of the large star would last longer. The collision aspect, I can't speak to other than once the collision is over the new large star will use it's fuel at a faster rate than the 2 separate smaller stars did.
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If planets orbit a star, and galaxies orbit a black hole (or something in the center), are clusters of galaxies orbiting anything? Second question inside
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While planets are gravitationally bound to their host stars, galaxies are a bit different. Galaxies have flat rotation curves, meaning, stuff on the outer edges of the galaxy aren't moving much more slowly than stuff closer to the center-- galaxies are usually home to dark matter halos. In a galaxy cluster, hot gas called ICM (intracluster medium) and way more dark matter inhabits the space through which these galaxies interact. This schematic breaks down when the influence of dark matter is small compared to the driving force of the universe's expansion: dark energy. Far enough apart, galaxy clusters will not be bound to each other, but helplessly pulled in space as it expands in all directions.
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If an explosion happens above water, can you swim down a few feet and not be hurt?
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actually yes.......depending on the size and type of explosive "During their small scale tests, the Mythbusters discovered that water can diminish the force of a shockwave caused by an explosion, giving credence to this myth. For their full scale test, the Mythbusters hung rupture discs 5 feet above water, 5 feet below water, and 10 feet below water at 5, 10, 20, and 50 foot intervals away from the explosives. They detonated 50 pounds of three different types of explosives above the water: gasoline, ammonium nitrate, and dynamite. While the gasoline could only rupture the closest above water disc, the ammonium nitrate ruptured every single disc and the dynamite ruptured all the discs except for the underwater discs located 50 feet away. With these differing results, the Mythbusters declared that the myth was plausible, depending on the explosive." _URL_0_
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How do we see light from a structure 30 billion light-years away when the universe is 13.1 billion years old?
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The universe has always been expanding. The photons left 13 billion years ago when the galaxy was much closer, but the galaxy they came from has been getting further and further from us during the whole time that the photons are travelling. So now that the photons have reached us, the galaxy that they came from is now 30 billion light-years away. However, the photons themselves have only traveled 13 billion light-years.
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Why doesn't the sun burn all of its hydrogen, etc., all at the same time?
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The Sun is kept balanced by the force of gravity trying to squish it all together, and outward pressure from the fusion reaction in the core. If the fusion were to be any faster, the increased pressure would make the sun expand, thus slowing the reaction. If it were to slow down gravity would start compressing it, and the reaction would speed back up.
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Why haven't humans and other animals evolved out of the need for sleep?
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For the same reason evolution hasn't given us laser eyes to shoot our prey: evolution doesn't create perfect adaptations for every situation, it is limited by available mutations and biological constraints (and is not an optimizing process, but that's a more complicated issue). Creating a human being/animal from some stray carbon, nitrogen and etc. is already an amazing thing, the fact that it takes a few hours of recuperation a night to keep the whole thing going is not that crazy. That being said, there are many possible benefits of sleep that could keep it around even if it were possible to 'evolve out of it'. In addition to giving the body a time to repair and restore itself, we also process and encode memories during sleep. Furthermore, we burn a lot fewer calories while sleeping; if you can find a safe place to sleep, or have another pack mate stand guard, then it's a lot better to conserve your energy by sleeping than to burn resources staring into the darkness with nothing to do.
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Why is there no video recordings of planetary fly by instead of just photographs, like Pluto etc?
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Here you go! _URL_0_ This is manipulated image data however, the cameras on New Horizons are not video cameras—specifically LORRI and Ralph. It will takes some weeks for all of the data to be transferred and analyzed by NASA/APL.
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Is it possible to have a liquid that is less dense than a gas?
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I don't know of any liquids less dense than a gas, but yes, the liquid would float on the gas in a closed system.
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If aging is caused by genetic damage, why not save healthy cells of each cell type when we are young and then clone and inject them when we are older?
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Ageing is not necessarily caused just by genetic damage. Thats a starter. And while your method can work for blood cells, its probably not going to work for "brain" "skin" and all. Just to point out some other things though: blood and marrow kinda mean the same, in terms of what cells you need to reinject (injecting marrow is enough). I don't know if you think that you can just inject cells in to the brain. Also stem cell is a term for a type of cell thats found in many places, its more like a category of cells rather than some type of tissue..
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Why we always hear about a revolutionary research with stem cells, but we don't have any revolutionary cure with stem cells?
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There are many clinical trials underway to use various kinds of stem cells for various diseases. The main reason why you're perceiving this big gap between discovery and use is that there are a lot of considerations before something can become a useful treatment. The discovery is generally, in a sense, a research article on the first handful of steps in the process. 1. Can the stem cell therapy do X in mice? 2. Can the stem cell therapy be safe in humans? 3. Can the stem cell therapy do X in humans? 4. Can the stem cell therapy do X in humans better than what we're doing now? 5. Can the stem cell therapy do X in humans consistently, and at a price that will make someone money? A paper can get published after answering question 1. A therapy will get used in your hospital considerable time after question 5 is answered.
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Why is there seemingly no controversy over stem cells anymore? What caused the controversy and was anything restricted that could have potentially lead to medical science advancements?
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From my understanding, the original controversy was over the ethics of harvesting stem cells from human embryos. Thanks to the work of Dr. Yamanaka (and the eponymously named "Yamanaka factors"), we can reverse fully differentiated cells back into a pluripotent stem cell form. These cells are often called iPS cells (Induced pluripotent stem cells). I believe there are some differences between them and embryonic stem cells, but the most attractive abilities of embryonic stem cells (namely the ability to become many different types of cells) are present in iPS cells. Furthermore, it would be rather impractical to rely on embryonic stem cells for new medical treatments because it would be very difficult to scale up due to the limited supply of embryos. Taking normal cells and converting them to stem cells is much more practical/scalable solution for future medical treatments. As a result, much of modern stem cell research revolves around these iPS cells rather than embryonic stem cells.
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If the sun, planets, and comets all formed from the same dust cloud, does that imply that the sun contains some amount of the same "rocky" material the inner planets are composed of?
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The sun contains some of the "rocky" material. These include all the larger atoms that you can find on Earth. All of them are just as hot as the rest of the material in their area of the sun, so they will all be just part of the sun's plasma. When the solar system was starting it had very little heavier elements mixed in with the hydrogen. So, as a consequence the sun has very little of them as well. The reason why the rocky planets have so much more rocky than hydrogen and helium is that when they formed they were not very big (compared to Jupiter for example) and any hydrogen/hellium was blown away by the sun once it started to shine bright enough and produce solar wind.
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Why does our ear and nose hair grow longer as we age?
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Its not that they're growing longer per se, they're growing for more time. The reason your arm, leg, ear, nose, etc. hair seems to stop growing once it hits a certain point has to do with how often there is overturning in your hair follicles. As we age, the turnover time increases, that is the peaks and valleys (growing and empty) spread out. For some, they become stuck permanently in the valley between production of hair strands -- this is baldness.
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When you are sick they tell you to cough up as much "infected" phlem as you can and get it out of your body, is coughing up and then swallowing it as effective?
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Normal lung secretions are designed to end up in the stomach. They are tracked up through the bronchioles and bronchus by cilia (small rhythmically-flailing processes). They reach the oesophagus and are then swallowed. Any pathogens trapped in these mucous secretions are then destroyed in the highly acidic environment of the stomach. As long as there are no breaches in your GIT integrity you should be able to do the same with mucous containing a higher viral/bacterial load with little consequence. Acid plus a thick mucous wall protects you, and will effectively remove the "infected" phlegm from your body.
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Do trees have a higher ratio of carbon 12 to carbon 14 than animals do?
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Organisms have an effect on the isotopic ratio of an element by preferentially uptaking lighter isotopes. The effect is that there are more ^(12)C than ^(14)C or ^(13)C in the tissues than in the environmental input. This process is called [isotopic fractionation](_URL_1_). In general we us [^(13)C](_URL_0_) (the stable heavy isotope of carbon) to evaluate C fluxes rather than ^14(C). ^(14)C is unstable, and therefore very useful in dating the time since the organism died, or process stopped. So, to answer your question, the isotope ratio will depend on the specific fractional uptake of the organism, as well as the initial ratio of the carbon input. In the ace of plants, they are fractionating atmospheric C, making it lighter. For animals, they are fractionating plant and animal matter, so could very well be lighter still.
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Outdoors, sunscreen wears out and needs to be reapplied every 2 hours or so. If you wear sunscreen indoors (away from UV radiation), does this same time limit on effectiveness hold?
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This is only true for organic sunscreens like avobenzone, but inorganic sunscreens like titanium dioxide or zinc oxide hold up a lot better. But back to your original question. No, it's the UV light that is absorbed and causes the molecule to breakdown. UV light is higher in energy than visible light, which in normal cases doesn't have enough energy to break chemical bonds (there are cases in which is does, but for the most part it doesn't.) How do we know organic sunscreens don't absorb visible light? It's because they are clear. If they absorbed visible light we would see them as colored. If the light isn't absorbed, it's not having a substantial effect.
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Do rockets use fossil fuels? Is there danger of running out of rocket fuel as we deplete oil reserves in the next 50-200 years? If so, are there alternative fuels that have the necessary power to take us into space?
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We are in no danger of running out of liquid oxygen or liquid hydrogen, as they can be extracted from water. You can make a workable rocket with just those fuels, although a big fat first stage full of low density hydrogen has penalties. Realistically, if absolute supply of kerosene or methane is an issue, we'll be too far gone to have the technical infrastructure to support spaceflights. Helium is the real supply danger. It's irreplaceable as a pressurant and coolant and it is a nonrenewable resource. It's plentiful in space, but in limited supply on earth.
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Will pressing my car brake pedal down in "bursts" make my brake pads last longer?
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edit: Based on a comment /r/ee58 made I realized I misread the test definition. Using more line pressure to dissipate the same amount of energy will use more pad material. ~~The relationship between line pressure and pad wear rate is roughly linear, so both methods will be similar.~~ The second method will probably use more pad material. _URL_0_ The better method is to bleed energy through engine braking.
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Do organisms with shorter lifespans evolve faster? If so wouldn't they always have the advantage over longer lived creaturea?
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Yes, they do evolve faster. For example insects can evolve resistance to herbicide within a single human generation. Not only that, but smaller animals tend to have larger effective population sizes which means that selection is more efficient (it can overcome drift even if the magnitude of selection is weak).
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Was there oil during the dinosaur era?
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Yes, there was. Much of our 'fossil fuel' comes from a time period known as the Carboniferous, which was about 300 - 360 million years ago, well before the time of the dinosaurs. This period is called the Carboniferous precisely because there's a high abundance of carbon in the rock record from that time. This is often preserved as coal or petroleum. Most of this carbon material derives from plants and algae, rather than the more familiar fossils of vertebrate animals. Dinosaurs did not appear until the middle Triassic about 230 million years ago.
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Are stars different now than they were at the beginning of the universe?
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Yes. Newer stars have higher metallicity, meaning they have a higher proportion of elements other than hydrogen or helium. These elements are formed at the end of a star's life cycle, so the later a star forms, the more of those elements is around.
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Are there any stars that still exist from the beginning of the universe?
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Those are called "[Population III](_URL_1_)"-Stars and have not been observed yet. We have no reason to assume that they don't exist, we just can't see them with today's telescopes. The [James Webb Space Telescope](_URL_0_) however should be able to detect them. By the way, the oldest known star is [SM0313](_URL_2_), formed only 100-200 million years after the Big Bang but being a Population II-Star, meaning it was formed out of the remnants of a supernova of one of those very first stars.
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When I'm filling a glass of water, why does the sound of the water entering the glass get higher in pitch as you pour more water?
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Variable pitches in a sound are due to the frequency of the waves in the sound. The more waves per second, the higher the pitch. Because of this, pitch is also indirectly related to the length of the wave since it is easier to get a short wave to a higher frequency. This is why bigger people and men have lower voices. Why tuba's have a low pitch and a flute has a high pitch. Or when a guitarist puts his finger on a fret, the string is shorter and the note is higher. When you pour water into the cup, the sound waves bouncing off of the walls of the cup are shortening, but the same amount of energy is being applied, so the pitch goes up.
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Why does the sound of water falling into a glass get higher as the glass fills?
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The sounds you hear as water fills a glass are resonant tones caused by the random vibrations of water hitting the glass interior and exciting resonant modes of the 3-dimensional glass object (the "resonator"). The portion of the glass filled by water does not vibrate as freely as the portion above the water level. The water "damps" vibrations of the adjacent glass. So as water fills the glass, only the portion of the glass above the water level vibrates audibly. Since the resonant frequency of an object is inversely proportional to the dimension of the object, as the portion of the glass above the water line decreases, it's resonant frequency increases...thus you hear a rising tone as water fills the glass.
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What is it that causes sweat to generally smell bad?
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It's not actually the sweat that smells bad, it is the bacteria living around the sweat glands. You'll notice that not all sweat smells bad, either -- sweat that forms on your forehead is not stinky. The sweat that smells bad is sweat that comes from apocrine sweat glands, which are associated with hair follicles, and they are found mainly in the armpits, external genitals, and perianal area, but also in small amounts around the nipples, inside the nose, and in the eyelids. However, the armpits and crotch areas tend to sweat more due to the skin not being exposed, and so they smell worse. They secrete a more oily substance, and this oil is consumed by bacteria that live in those areas. It is the bacterial decomposition of the oils that causes the odor, not the sweat itself. Non-apocrine sweat glands don't cause significant odor because they secrete a more purely aqueous sweat that doesn't have much for bacteria to eat.
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I have a typical 1L soda bottle, when I pour 100ml of 91% isopropyl alcohol inside and ignite the cap it burns slowly around the cap for only a few seconds then extinguishes. However, if I only have 10mL of the same solution and do the same thing it burns much more violently. What is happening?
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If there is not enough fuel or not enough oxygen then the mix wil be outside the [flammability limits](_URL_0_) and not burn at all. Your mix was likely way fuel-heavy. You need to get the mix just right for a near-stoichiometric mix and a fast burn. This will be announced by the flame burning back into the jug instead of just near the mouth where it has excess oxygen and possibly a small bang. Try one drop of alcohol in a milk jug and then shaking it. Or don't - fire, explosions, melted plastic, what could possibly go wrong? No milk jugs or soda bottles blew apart and hit me in the eye when I was younger and stupider but I would recommend goggles, gloves and a bucket of water as minimal safety gear.
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Why is the kilogram the 'base unit' of mass instead of the gram?
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Are others actually reading his question? Yes when using metres of things they are more likely to weigh kilograms but why define a gram as 1000 times less than what would be used with other base units? The original kilogram was 1 dm^3 of water. So why not define *that* as a gram?
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Why is the kilogram the base unit for mass and not the gram?
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[Kilogram](_URL_0_) Wikipedia has a nice history section that describes how it came to be. Essentially the French came up with an official method of describing a gram, one cubic centimeter of water at 0C. But bothering with water and small units would be to troublesome so they came up with a solid artifact with a weight more convenient to trade, the kilogram.
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Why can completely paralyzed people often blink voluntarily?
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Blinking is a motor function controlled by the facial nerve, the seventh cranial nerve. Cranial nerves come directly from the brainstem, bypassing the spinal cord. Cranial nerve reflexes are often used to assess levels of brain function (diencephalon, mesencephalon, and medulla).
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Can stress or intense fear actually cause your hair to turn grey?
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scientific american article on this _URL_0_ Excerpt: Does stress accelerate this demise of the melanocyte population? "It is not so simple," Fisher says, noting that the process of graying is a multivariable equation. Stress hormones may impact the survival and / or activity of melanocytes, but no clear link has been found between stress and gray hair. NB Melanocytes are where melanin (brown pigment) is produced
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Will the asteroids in the asteroid belt eventually clump together and form another planet?
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The total mass of the belt is about 4% the mass of the moon, so there's just not enough there to make a planet.
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