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Why do planets and moons tend to have orbits within a single plane, whereas some galaxies are relatively globular? | The key is collisions. A random blob of particles (stars, gas, dust, your n-body computer simulation) which are influenced by gravity and have the potential to collide with eachother is very unstable. Particles will lose momentum in collisions and the blob will collapse. Conservation of angular momentum will amplify any initial rotation, and eventually one particular axis of rotation will win. Disks are more stable than blobs. This is why there are so many disk-shaped things in astronomy, such as spiral galaxies and protoplanetary disks. The solar system formed from the leftovers of the disk which became the sun and that is why everything is more or less on the same plane. Anything blob-shaped hasn't had a lot of collisions. Gas clouds are highly collisional, but stars are small enough that it is unlikely. |
Why don't we cut CO2 emissions by putting "scrubbers " at the end of smokestacks and exhaust pipes on cars? | > I understand that we have these devices called scrubbers that can absorb CO2. Why don't we use scrubbers at the end of exhaust pipes and smokestacks. There is no such thing as "CO2 scrubbers". There is a process for [capturing CO2](_URL_0_), but that requires a lot of energy. From wiki: "Capturing and compressing CO2 may increase the fuel needs of a coal-fired CCS plant by 25–40%.[4] These and other system costs are estimated to increase the cost of the energy produced by 21–91% for purpose built plants.[4]". Without even taking any other variables into account, giving up 25-40% of fuel efficiency for the sake of capturing CO2 is a non-starter. Also, once captured, you need to store it somewhere. The plan with "clean coal" is to pump it deep under ground and hope it stays there. Obviously this can only be done on a (stationary) power plant, not in a (moving) car. In short, CO2 capture is a ridiculous idea even for power plants, and is completely unworkable in cars. |
Why can't we put some sort of filter over the exhaust of a car to reduce harmful emissions? | We already kind of do that with the catalytic converters. They are like sponges through which exhaust gas have to pass. The metal sponge is coated with catalysts like platinum that helps break down harmful combustion products like NOx, CO and unburned fuel. They are typically broken down into oxygen, water and CO2 which are a lot less toxic. |
If space / the universe is constantly expanding, does that mean the strength of the vacuum of space is increasing proportional to the speed at which the universe is expanding? | Well, the [vacuum](_URL_1_) in interstellar and intergalactic space is already pretty strong compared to what we typically make on earth. The expansion of the universe is would help to decrease the density in these regions by creating more volume, but it won't change too quickly. There is plenty of uncertainty in how long it will take the universe to double in size, but it will be on the order of billions of years. And that only brings the average density down by a factor of two. Since we now think we live in an [accelerating universe](_URL_0_) this rate of expansion will eventually get much faster, but you'll need to wait a while for that to kick in. |
Why Can't Dogs Eat Chocolate? | Chocolate contains theobromine, which is poisonous to many animals (including humans, in large quantities). That said, a lot of items like cheap chocolate, brownies, or other "chocolate" foods don't really contain enough actual cacao to poison, say, your average yellow lab. Dark, high quality chocolates contain much more and are a more serious risk. Interesting note: The effect of this stuff on dogs is quite a lot like caffeine. One of my dogs once got into some chocolate (about 1/2 lb) and was unbelievably hyper and simultaneously quite sick for about 24h. We're talking full speed laps around the front lawn with bouts of puking at each apex. |
Why do we have accents? | Not much to add to slightly_offtopic's excellent answer! The only thought I had was how my linguistics teacher used to say "All human beings are especially good at one thing: failing to say the same thing *the same way* more than once." In essence, that's why there are accents. |
Would the asteroid belt eventually form a new planet? | No, it's actually the other way around. Jupiter prevented the material in the beld to coalesce in the first place. The gravitational influence destabilizes the orbits in a way, that the objects could never merge and form a larger object. Even then, the newly formed object couldn't be compared to the other planets, as it wouldn't have half the diameter of our moon. |
Why do bread and other food products of the sort become stale? | Flour is mostly starch. In flour, the starch is in tightly wound coils, with lots of small branches coming off the coils. As you bake it, you force water into the coils, loosening them up, like stretching out a spring. This is why flour is firm and extremely dense in dough, but loose and soft once you've baked it, even if you didn't leaven it. If you leave bread out in the open air, water slowly evaporates out of the starch molecules, and the starch springs tighten up on themselves again, making them stronger, and therefore making the bread harder. |
Why don't the other gas planets in our solar system have rings as profound as saturns? | Saturns rings are mostly made up of ice and other such reflective materials. Also as you can tell there is alot of pieces in saturns rings compared to other planets so there is just more to see. While other planets why they may have rings there just isn't alot of material or material that has a high enough reflective state to make them that noticeable. Edit: Also to add one of the main theories as to how saturns rings came to be is that one of it's moon somehow got destroyed (Too close to saturn/collision with another object) and that left alot of objects left to orbit saturn. That is just one of the theories behind why saturn has rings but we still can't say for sure. |
Can diesel explode due to suction rather than compression? | Not really. Diesel requires compression to raise the pressure (and as a consequence the temperature) of the air to their combustion levels. This is why the pistons exert pressure on the gas in the cylinder. The vacuum you'd create by applying suction to this gas would neither compress nor heat it, therefore combustion wouldn't occur without some type of ignition source. |
[Psychology] Why do major chords sound "bright" and "happy" while minor chords sound "dark" and "sad"? | There isn't really a conclusive answer. The question has come up a few times before ([here](_URL_2_) and [here](_URL_0_)), but the **tl;dr** is that it is probably culturally learned since some cultures don't have the same emotional response. The dark/sad sound is actually termed dissonance and comes from tritones. The sense of "evil" from the sound is so widespread in (most) western cultures that it was even termed "diabolus in musica" - the devil in music. Forgive the wikipedia link, but you might enjoy the section on its [historical uses](_URL_1_). |
Why do minor chords sound "sad", and major chords sound "happy"?? | It's mostly a societal thing. In western culture we are trained to understand minor as sad and major as happy, but that's not the case in many cultures. The same goes for rhythmic divisions. Throughout western music history, the overwhelming majority of music is in 4/4 time, so this sounds normal to us. In other cultures, such as eastern European countries, folk songs in 5/8 or 7/8 are very common. It really comes down to the musical traditions of the culture one is raised in. |
Is there a limit to the number of photons that can exist in a given volume of space? | Yes. Even for photons, there is a finite limit. Photons contribute to the stress-energy tensor for some given locality. Increase the energy density enough in this one space and you will form a black hole. ~~though pair production would occur long before you got the necessary energy density through photons alone to form one.~~ |
Is there an upper limit to how many photons there can be in a given space? | Photons are not restricted from occupying the same quantum state like a few other particles are (electrons obviously), so we wouldn't have to worry about anything like the Pauli exclusion principle getting in the way... In fact, the ability of a photon to exhibit this behavior is where we get the ability to make lasers and the like. Now if you want to gather up all of the photons and sit them in one place, I would have to assume a singularity and black hole would inevitably follow, but I will leave that part up to someone who is more qualified than I to answer. That is a pretty interesting prospect. |
why is it possible to understand a language but not speak it? | Language production and language understanding are controlled by two separate parts of the brain. Language production is Broca's Area: _URL_0_ Language understanding is Wernicke's Area: _URL_1_ Damage to Broca's Area would result in an inability to speak even though you could understand language with an intact Wernicke's Area. |
Why can we understand a language but not speak it? | Another thing to keep in mind with language is that practice makes perfect. He isn't practicing his Arabic speaking, so it isn't getting any easier for his brain to process it, but he still practices listening. Doing this for a long enough time would create a gap between his and your speaking abilities. All he has to do is start speaking Arabic more and he'll quickly be able to speak it as well as you. |
Are there any gaseous planets with a similar atmospheric composition as Earth? | There might be, but they're probably not very common at all, for two major reasons: 1.) Earth's atmospheric composition is *heavily* influenced by photosynthesizing organisms, which might have a much harder time evolving on a gas giant. 2.) A planet (or rather, protoplanet) massive enough to hold onto a deep atmosphere would have a much different atmosphere from Earth almost by default, as it would have gravity sufficient for retaining hydrogen and helium, even if it were much warmer than the gas giants in our Solar System. |
Are there any examples of animals that behave monogamously? | Yep. Take a look [here](_URL_0_); the sorts of animals that are monogamous are actually pretty diverse. |
What determines the color of urine? | The yellow component of your urine is actually bile (same stuff that makes your poo brown). In the body, heme is broken down into bilirubin which is then secreted into the gut with bile. Some of it gets re absorbed in the gut and from there is in the proper form for the kidneys to excrete it into the urine making it orange/yellow. The intensity of the color is determined by the amount of water diluting the color out. |
Is it mathematically significant for sets of consecutive numbers to add up to a prime number or does it happen often enough that nobody cares? | The sum if consecutive numbers from a to b is (b - a + 1) * (a + b) / 2. The only ways that works out to be prime is if: * b - a + 1 is prime and a + b is 2 * b - a + 1 is 2 and a + b is prime If a + b = 2, then you are looking at a = 0, b = 2, 0 + 1 + 2 = 3. If b - a + 1 = 2, then b = a + 1 and a + b is prime. But a + b = a + a + 1 = 2 * a + 1, so for every odd prime p = 2k + 1 you have a = k, b = k + 1, a + b = p. In other words, this only happens for 0+1+2 = 3 and for k+(k+1) = p when p is prime. In other words, it's an entertaining thing for me to do in 2 minutes on reddit, but without any profound practical or theoretical significance. |
How Closely could Two Planets Orbit Each Other? Would their proximity have any effects? | There is a concept called [The Roche Limit](_URL_0_), where two orbiting bodies can tear each other apart by their own tidal forces if they orbit within this limit. As you can see there is a formula for it. Which can be simplified if you are looking at two bodies of *equal* density and radius, like Mars: Assume radius of Mars: 3390 km Roche limit = 1.26 * 3390 km = **4712 km** So the answer is, they don't actually have to collide before you start to see problems. |
Why do people itch? What exactly is an "itch"? | It's your sensory neurons telling you that there's something irritating your skin. It could be caused by a parasite of some kind, so it's beneficial for you to scratch and remove said parasite. The irritant could be mechanical (insect bite) or chemical (mosquito saliva). |
Why can't we use smaller wavelengths of light instead of electron microscopes? | Electron microscopes can get in the order of 50 pm resolution, while diffraction based systems rely on the wavelengths (as you've picked up on). However to get down to 50 pm visual resolution, you need light with a wavelength in the order of 100-150 pm. This is down in x-ray territory, so you need to have a source of x-rays that you can use, and the surface you're looking at needs to be able to reflect said x-rays in a meaningful manner. Since x-rays love to pass through things, they're not very practical. (And might damage the sample, depending on what you're looking at.) [The wikipedia page on diffraction limited optics](_URL_0_) is probably of interest to you. |
Why can we only dream while asleep? | Interestingly, when taking the Amazon plant mixture, Ayahuasca (and this is true with other tryptophanes I believe), often, you only experience the visions (which are like vivid dreams), when your eyes are shut. You can be deep, tangled in a vision and then open your eyes, and "boom", you are completely sober, looking at the 3-d reality of this world. Close your eyes again and woosh, you are back in the moving picture world again.... weirdest feeling.... |
If light passing through air makes the object seem blue from far away (like mountains), why don't all the planets look blue? | The atmosphere does have an effect on the observed color of the planets. Astronomers have to correct for atmospheric effects such as Rayleigh scattering (the cause of the blueness of the sky) , which is one reason why it is better to situate telescopes on mountains or in space. |
Why did the big bang not result in the creation of a black hole? | This question has already been answered here. _URL_1_ _URL_2_ _URL_0_ |
Do plants of the same size give off the same amount of oxygen? | Oxygen is a waste product of photosynthesis. Different plants can have different maximum photosynthesis rates. Mechanism like [photorespiration](_URL_1_) and [non-photochemical quenching](_URL_0_) can reduce photosynthesis rates. At higher lighting levels plants are going to be CO2 limited as to their maximum photosynthesis rate. Different plants can also have various values of [leaf area index](_URL_2_) so this question is a bit too broad to answer. But the best houseplant for good fresh air would be one that is receiving a lot of light to take in more CO2 and emit more O2. |
Why do clouds become dark when it's about to rain? | They are just the thickest clouds that block out the most light. Rain also does a good job of scattering light, so some of the darkness is actually the raindrops blocking light as well. They look blue/dark blue because blue light has the best penetrative properties. The blue light does not get absorbed very easily, so it's the only light that makes it down to the low parts of the clouds. So in the end a mixture of no light and blue light makes storms look dark blue. |
Why are rain clouds dark? | It says there are 6 comments but I don't see any... So to the question: rain clouds are dark simply because they have a lot of moisture in them, and that moisture also carries lots of little dust particles and random stuff. When it becomes dense enough it falls as precipitation, but until then it's just that there's so much "stuff" in the cloud that it blocks a lot of the light. If you walked through a really transparent cloud you probably wouldn't feel much. If you walked through a rain cloud you'd come out the other side soaked. |
Is infinity (∞) ever used in mathematics in a practical way? Or is it just an abstract concept? | What do you mean by practical? The [Central Limit Theorem](_URL_0_), probably one of the most important theorems in math (and most used in practice) is the statement that a particular limit at infinity has a particular form. Infinity is then required to justify any use of the Central Limit Theorem. |
Why is the sun bright when it's rising yet dim when it's setting? | It is most likely caused by the amount of air pollution and dust present at dawn and dusk. During the day, you have the maximum amount of industrial activity, so more smoke, dust and other particles get pushed into the air. You also generally have more wind during daylight hours to keep any dust in the air. The more stuff in the air near the horizon, the less bright the sun will appear. During the night, most of the dust and pollution settles or moves away so there is less obstruction at dawn. Also, from several years of waking up before dawn for work, there is rarely any wind in the early hours of the morning, so dust has a better chance of settling closer to the ground instead of being swept up into the air. |
Do plants and humans share a common ancestor? | All life does _URL_0_ Edit: It looked like a single celled organism |
Why don't we use photosynthesis for solar power? | It's not because nature does something, it is automatically the most efficient way. Photosynthesis efficiency is about [0.1-2%](_URL_0_), commercial solar panel efficiency (polycristalline silicon) is about 16-18%. Edit: changed "solar cell" to "solar panel". Solar cells in themselves have a slightly higher efficiency (about 20%). Solar panels lose efficiency because of (among others) the gaps between the individual solar cells, losses in wiring etc.. |
Why does adding ethanol to gasoline reduce fuel economy? | Ethanol has an energy content of ~21.2 MJ/L while gasoline has a higher energy content of ~34.8 MJ/L. Because of this you must burn more ethanol to equal the combustion of pure gasoline. Check this table for the energy content of other fuels: _URL_0_ |
With nothing but hydrogen and oxygen, how come water isn't flammable? | For the same reason CO2 isn't, and the same reason an anvil on the ground can't fall on your head. Water is what you get when hydrogen is burnt. It's already ashes. You can't burn ashes. Scientifically: Water is at a very low energy state. For a chemical reaction to release energy, it has to move from a high energy to a low energy state. Many explosive compounds have lots of nitrogens hanging off at unhappy angles. Nitrogen likes to form a sturdy triple bond with itself, so when its hanging off a chemical its like stretching a rubber band- a lot of energy is stored. When the nitrogen is liberated, it snaps together with another nitrogen atom and all the energy gets turned into velocity and jiggling, aka pressure and heat. |
What happens if you kept vodka in the freezer then added an ice cube? | If you do it right, you can freeze distill the vodka. A dilute solution of water+ethanol will freeze onto the ice cube, leaving a solution of enriched ethanol behind. _URL_0_ |
Is there a method to find an infinite series for any irrational number? | Your question is strange because you have to provide a "coding" of your irrational number, and this is where the problem is: You cannot define in English, or more generally with a finite number of symbols, all the real numbers. Given a formal system, the set of "formulas" is enumerable, hence the number of "definitions of real numbers" is also enumerable, hence the number of "undefinable real numbers" is infinite and non enumerable. Now, if you select any real number x in [0, 1[ and provide me with a function f: N - > {0, ..., 9} that gives me the successive digits of x (e.g. if x=0.245, we have f(1) = 2, f(2) = 4, f(3) = 5, f(4)=0, f(5)=0, etc.) then, trivially, the series z(n) = \sum_{k=1}^ n f(k)/(10^ k) is a series of rational numbers that converges to you irrational number x. |
Is it known how far the sun moves in our Galaxy in relation to an earth orbit? | _URL_1_ NASA says 828,000 km/h, or 230 km/second. It takes millions of years to do a lap of the milky way, so we wouldn't be able to see our trash in any meaningful way. By comparison, the Earth orbits the sun at just under 30 km/second, so there's no way we'd catch our garbage one earth orbit later either. Source: _URL_0_ From an orbital mechanics standpoint, we couldn't ever just drop our stuff in space anyway. To be on the same orbit as the Earth, it has to be moving the same speed as the Earth. One exception is if we managed to fire an object directly towards or away from the center of the milky way, then orbital mechanics says that one galactic orbit later it would come back and pass through the earth/sun system again. |
Is there a maximum size of planets? | According to one definition, at around 13 Jupiter masses (~2.5×10^28 kg), a planet can sustain deuterium fusion and goes from being classified as a gas giant planet to a brown dwarf star. The difference is somewhat arbitrary though and isn't universally agreed upon. See the following link for more info: _URL_0_ EDIT: Quoting relevant part of the link above: > Astronomers vigorously debating that se- mantic question fall mainly in two camps. One advocates a definition based on formation—a brown dwarf condenses out of giant molecular clouds, whereas a planet forms via core accretion in a circumstellar debris disk. The other focuses on interior physics: A brown dwarf must be heavier than the mass threshold for core fusion of any element, roughly 13 Jupiter masses (...) |
Why Solar Eclipses don't happen monthly ? | The moon rotates around the earth with an orbit at a different angle than the moon rotates around the sun, so the planes of the orbits have to align as well as the location of the moon relative to the earth and sun. |
Why does damp clothing eventually dry out if left hanging in a dry, room-temperature environment? | Your understanding of water is flawed. The damp clothing is simply drying off through evaporation. This occurs because the room temperature air is hardly at saturation point. Water vapor exists in the air at nearly all temperatures and air can hold quite a bit of water vapor at typical environmental temperatures. _URL_0_ |
How far are we from neural network based programs that will be able to generate speech from text based on provided voice records, that will be indistinguishable from real voice? | We are already at the point of being able to produce kinda-good speech from text with only limited example text. Take a look at _URL_0_ for an example of the state of the art. The trick, though, is "indistinguishable." That's hard to judge and may be very, very far off. For use in video games, for instance, a perfect text-to-voice agent would need to effectively be a great actor, which in turn implies that it's aware of the context of the text and its intended emotional impact. That is, in of itself, a crazy hard problem that we're far from solving. |
If gravity acts upon objects with mass, and light is made of photons (no mass), how can gravity 'bend' light? | In general relativity, gravitational mass distorts spacetime. Near to very large masses, this distortion gets large. The light is still travelling in a straight line in its local spacetime, it's just that a straight line near to a large mass looks bent from far away. It's like lines of ~~latitude~~ longitude: they're always straight, and at the equator they are parallel. Despite being straight and parallel, they meet at the poles, because the surface of the earth is not a Euclidean flat surface. Edit: Gah, brain fart... I knew I'd make that mistake somewhere. |
Was the Integral "made" such that to be the anti-derivative or did it just so happen that it acts as an anti-derivative? | I believe that the latter is a more accurate telling. It's more that the processes of integration and differentiation were discovered and proofed as inherently inverse of eachother. I think the idea of creating calculus with an end game in mind is simply a misrepresentation. I don't know if that helps answer your question much but some quick googling around the fundamental theorem of calculus might help clarify some of this. |
When the sun eventually transforms into a red giant, why are the inner planets predicted to be engulfed and why won't their orbits just expand outwards with the sun's expansion? | The orbits of the planets are a function of the Sun's mass - when the Sun expands to a red giant, its mass will still remain the same, so there is no reason why the orbits of the planets would change as it expands. |
Cooling without fridge? | Not really helpful during a power outage, as this is more of a camping tip: Put a bottle in a wet sock and hang it outside. As the water evaporates, the temperature of the bottle (or any other object in the sock) will decrease a couple degrees. This is because the vaporization of a liquid consumes heat energy, which will lower the temperature of the sock. Then the bottle will lower in temperature as well due to conduction to the sock, until an equilibrium is reached. Do not expect to cool a beer to fridge temperatures, but this can surely help to make a beer much more enjoyable on a hot summer day when there is no fridge near. This will work better when it's windy outside, because the wind will cause the water to evaporate faster. |
If washing chicken in dangerous, then how can I wash anything with chicken bacteria? | The point against washing chicken is that it is an unnecessary spread of bacteria as there is no benefit to washing it. Obviously a cutting board needs to be washed so washing it is a reasonable action. |
If you put a hot object into space does it cool down and if so is it faster or slower than when the same hot object is in an atmosphere (of a lower temperature)? | On a human scale, there's no real conduction or convection in space. However, *radiation* can transfer energy. If you put a hot object in a vacuum, it will radiate energy in all directions - the hotter it is, the more energy it spits out. If it spits out more energy than it receives, then it will cool down. Whether it will cool down faster on Earth than in space depends on a lot of things though. It depends on what colour it is - i.e. how much radiation from the Sun it absorbs - what the weather is like on Earth (is it cold? windy?) etc. But things can cool down in space. |
Do non-human animals need glasses? | I recall a study of a population of Inuits in Alaska, who had only recently adopted a "modern" lifestyle. In this group, the elderly were not myopic whereas the younger generation saw a substantial increase in cases of myopia. So if we taught rhesus monkeys to read under artificial lighting and to focus on other nearsighted tasks, perhaps they'll develop a need for vision correction. |
If a gas giant and a rocky planet (such as Earth) orbited a star from the same distance, would they have the same year length or orbital speed? | Yes, a planet's orbit is what determines it's speed. Check out [Kepler's Laws of Planetary Motion](_URL_0_), specifically the third one: > The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit. This basically says that the speed at which something orbits *only* depends on how far away it is from what it's orbiting. The mass of the object doesn't matter at all. |
Quick question - with all this deep space telescope stuff recently, how come these extremely deep space pictures aren't blocked by stars at some point? | I suppose you are talking about images like [this](_URL_0_)? The thing is, that each dot in this image is an entire galaxy. Galaxies are stacked in so called "clusters" which are held together by gravity. "Stray" galaxies, or even stars do not (or hardly ever) exist. Furthermore, this image was taken by deliberately pointing the Hubble Telescope at a spot in space that appeared to be entirely black. Thus it is not a coincidence that there are no close stars or galaxies in the way. |
How do heat-shrinking plastics work? | Think about a piece of licorice that you put in the freezer. If you were to stretch it before and during the freezing process, the licorice would remain stretched until it warmed up. Same deal with the heat shrink tubing. It’s in a prestressed state when you buy it and returns to the unstressed smaller size when heated. |
On a molecular level, what is it that makes some substances 'sticky'? | I don't think "sticky" is something that has a precise meaning in chemistry. I think what it comes down to is the relative strength and balance of many types of [intermolecular forces](_URL_1_) that are at play. Take honey for example. It has lots of carbohydrate molecules like [fructose](_URL_0_). This molecule has lots of hydroxide groups dangling about. These -OH groups can initiate [hydrogen bonding](_URL_4_) with other similar sugar molecules. As a result, you get a fluid that has a very high viscosity and is quite sticky. Contrast this with [tar](_URL_2_). Most of it is a mixture of hydrocarbons, all tangled up with each other. Here it's [van der Waals forces](_URL_3_) that are important. |
How come all the planets seem to be on an even plane around the sun? | Angular momentum. When the solar system was young, it was a cloud of gas & space dust. Although the motion of each individual particle may have been erratic, the cloud had some net rotation in a certain plane. As the dust & gas began to collect into larger bodies over time, the particles travelling up, through the plane of rotation and down through the plane of rotation collided and cancelled out. As a result, the cloud over a long period of time flattened into a disk, and the rotation speed increased. |
Why is Earth the most dense planet and Saturn the least dense? | Earth is the densest planet for two reasons: it is made of dense material, and it is heavy. Both points need a bit more elaboration. Compared to a gas giant, Earth is dense! The average chunk of Earth (which is the average value of crust, mantle, all that) weighs over 5.5 grams/cm3. The gas giants have a much lower density due to consisting mostly of, well, gas. However, this is not all there is to Earth's great density. After all, a metal-rich planet like Mercury should theoretically be denser than a rocky planet like Earth. However, because Earth is much heavier than Mercury, its core is more compressed and therefore far more compact than it'd otherwise be. This is also why Earth is slightly denser than the less-heavy Venus, despite the two being made out of similar stuff. |
Why do you get the "pins and needles" sensation after a limb wakes up? | A nerve was compressed. When this happens you'll lose mobility and feeling of the arm. Most people think your blood circulation was cut off but that's not true. The pins and needles come from your nerve "getting back online" so to speak and restoring function. |
Why do all planets in our solar system orbit in the same direction on the same plane? Is it possible for a solar sytem to have orbiting planets that resemble an atom? | All of the planets formed from the solar nebula, a single large cloud of gas. The cloud of gas collapsed into a disc, and the planets formed from that disc, which means they all orbit the same way that the original disc did. This should be the same in any planetary system, so planets orbiting in nice circular orbits in the same direction should be the norm. However, weird things do happen. Random close encounters can drastically change the orbit of a planet. A star could capture a rogue planet. So you'd expect a small number of planets to have odd orbits. With smaller objects like asteroids, little interactions have a bigger effect, so these things tend to scatter around a bit more. So even though most of the asteroids are in the disc of the solar system, there are a decent amount that are above or below or in weird orbits. Comets can orbit backwards too. |
If the expansion of the universe is supported by cosmic microwave background radiation, how can the universe be expanding exponentially? | The expansion of the Universe **now** is controlled mainly by dark energy (~70%) and matter (~30%, composed of baryonic and dark matter) and there is no significant contribution from radiation (including the CMB). Ignoring matter for simplicity, dark energy makes the Universe expand exponentially, meaning the scale factor (the size) is an exponential as a function of time. As space is stretched, the CMB gets colder as the wavelengths get longer. However, there is an inverse proportionality between the CMB's temperature T and the scale factor a, not a linear relationship between T and the volume a^(3) as you claim. Still, there is no contradiction. One is a relationship between T and a, and the other is between a and t. |
When I am tired, my penis is more sensitive than normal and I am more prone to getting erections. Why? | Erections are related to your parasympathetic nervous system. The Parasympathetic nervous system is responsible for "rest-and-digest" bodily responses, including sexual stimulation. The parasympathetic nervous systems works in a complementary relationship with the sympathetic nervous system. Read more here: _URL_0_ |
Why do I get erections when I'm tired? | On a similar note, why do I get a semi-erection when I need to urinate? |
Is it possible for a planet to rotate about two axis' at the same time? | In 3D space, rotations on any number of axes can be reduced to rotation about one axis - so any planet that rotates about two axes is merely rotating about one axis that's the sum of the two rotations. |
How large would Jupiter appear in the sky if it occupied the same spot as Venus? | Here is a video that shows what each planet would look like next to earth if they were as close as the moon. I know you asked Venus, but maybe this would put it in some perspective: _URL_0_ |
If we lived in a colony on one of Jupiter's moon, how big would Jupiter appear in our sky? | If we lived on Ganymede, it would appear about 16 times as wide as the moon and the sun do from Earth. |
Can you pop popcorn by freezing it? | Considering water only expands by ~10% when frozen, I'm going to have to say no. There is also very little water in the kernels so that doesnt help. You might notice a change in size, but that would be at a maximum. You'd likely just end up with cold kernels. |
Why can I balance on a bike when its moving, but not when its stationary? | There is no one simple answer here, but Andy Ruina and his collaborators have probably done the most to elucidate the dynamics of bicycles. I'd recommend starting with [this video](_URL_1_) of Ruina explaining the physics. If you want to go more in depth, you can poke around [his web pages](_URL_0_). |
how can there be gas in space ? | Hydrogen has a melting point of 14 K *at atmospheric pressure.* When there's hardly any pressure (i.e. in space), things can remain a gas at lower temperatures. In the same fashion, a glass of water would boil in space. |
Why do I have to adjust my focus when looking between my face and objects far behind me in a mirror when the reflections of both objects are the same distance from my eyes? | The mirror doesn't change the focal point. Think of a flashlight beam diverging for some time then striking the mirror and being projected on a wall. The diameter of the spot actually striking the mirror will be smaller than the spot projected onto the wall. The mirror only changes the direction of the light, but preserves the relative angles of incidence and therefore the divergence (or in this case, convergence, as everything comes into focus at your pupil). |
How do we differentiate between memories of real life and realistic dreams? | The only way to remember a dream is to wake up dreaming. We immediately recognize it as a dream as our mind scrambles to put together the story. If we sleep through the dream we don't process it and store it as a memory. Thus we automatically remember dreams as dreams because we have to recognize them as dreams to store them. |
Where does all the pollen we breathe or otherwise ingest end up? | Through the action of the mucociliary escalator. A thin layer of mucus coats the inside of your lungs. This mucus captures dust and particles that enter your lungs. Once the particles are captured, cilia lining your airway wave the fluid up the sides of your lung airways. You then typically swallow it and maybe spit it out. |
Where does the fat in fruits and vegetables come from? | Plants and animals make fats from glucose, with several intermediate steps. [here](_URL_1_), [here](_URL_2_), and [here](_URL_0_). (Warning, lots of chemistry). |
Chemically, what differentiates a good shampoo from a bad one? | Agree with *EagleFalconn* on all of the above/below. The science and claims behind conditioners and anti-frizz products are not as tenuous as you might first assume. Some conditioners actual use [*quaternary ammonium salts (quats)*](_URL_4_) for their [anti-static](_URL_4_) properties. As the quats used possess positive charge, they negate the negative static charge that accumulates in hair, thus preventing the 'frizz'. [This](_URL_3_) was an interesting (if quite basic) programme shown on the BBC recently (not sure whether you'll be able to get it outside of the UK), discussing the chemistry behind cosmetics. |
Do hairs really grow faster and stronger after being shaved with a razor or is that a myth ? If so ,why ? | No; the ends of the hairs are merely blunt instead of tapered, which makes it seem like they are growing back faster/thicker. |
How come can we theorically see the light of the big bang with a telescope, yet exist at the same time? | The Big Bang was not an explosion in space, and it didn't happen at some point, it happened everywhere. The cosmic microwave background is everywhere and going in all directions, just like the matter is everywhere. This is an extremely frequent question and it is answered [in the FAQ](_URL_0_). |
How old is the moon? | The moon formed between 10 and 30 million years after Earth did. This modeling is based on using isotope traces of the process and the region for that age range is that if you accrete Earth really quickly then the moon needs to form late and if you form Earth slowly then the moon needs to form really quickly after Earth is essentially done forming. The attempts at directly dating the moon have not been too good since there was probably a global magma ocean which would have delayed the formation of solid (ie datable) rock. The other way to go is to use Lu-Hf data and calculate a model which generally agrees with what I wrote above (though the error bars are larger). |
How do thrusters work in space? | Engines used for space travel, whether they are solid rockets, liquid rockets, gas jets, or ion thrusters, all work by ejecting particles having mass in the opposite direction of the intended direction of travel. It's not about "pushing off," but rather, sending mass in one direction. Conservation of momentum says that if a spacecraft pushes particles of exhaust gas or ions in one direction, the spacecraft must travel in the opposite direction to conserve momentum. |
How much alcohol can I add to my orange juice before it will no longer freeze in a freezer? | It depends on how cold your freezer gets, and how strong you make your drink. The 'standard' setting for commercial freezer/refrigerator units is usually around -20C, which will freeze an alcohol/water solution of around 30% alcohol by volume - weaker than straight vodka, but almost certainly stronger than your screwdriver. Assuming an 80-proof vodka, you could only add 33.3mL of orange juice to 100mL of vodka to hit 30% abv - at a 3:1 ratio, you're not drinking a screwdriver, you're drinking vodka with a shot of orange juice in it. A better bet is to chill the orange juice in the refrigerator, the vodka in the freezer, and invest in some quality insulated drinkware. Personally, I drink out of a converted Dewar flask, but I will understand if you think that is going too far. |
Why does the pitch of music drop while yawning? | Are you sure it is not just a change in timbre? When I yawn I mostly hear a change in timbre, which can sound a bit like a change in pitch.. |
Why can't we add more lenses in a telescope? | The problem isn't making it longer, but wider. The resolution of a telescope depends on how much light it can get from a given source, so telescope with wider apertures have higher resolution. Adding more lenses would just focus and unfocus the light. |
Water vapor is Earth's primary greenhouse gas both in quantity and effect. What prevents the cycle of the atmosphere heating, thus able to hold more water, thus heating the atmosphere even more, and so on? | Good question! It's a positive feedback loop, but the "gain" is less than 100% so it eventually reaches an equilibrium. To put rough numbers on it, if some factor like CO2 increases temperature by 1 degree, that will allow the atmosphere to hold more water vapor, enough to cause a further greenhouse warming of about 1/2 degree. That will increase water vapor enough to cause a further warming of 1/4 degree, which causes 1/8 degree of warming, and so on. So the total warming is 1 + 1/2 + 1/4 + 1/8 + .... which [adds up to](_URL_0_) 2 degrees. The water vapor feedback loop doubles the sensitivity of the atmosphere to CO2, but it doesn't cause infinite warming. However, the 1/2 factor I gave is for the current Earth atmosphere. If Earth were closer to the sun and thus hotter, you'd get a lot more water vapor from a given amount of warming. You could potentially have a situation where 1 degree of warming gets you 2 degrees gets you 4 and so on, which would lead to a "runaway greenhouse effect". |
Is the asteroid belt going to become a planet eventually? | Well, [Ceres](_URL_0_) is by far the biggest object in the asteroid belt and makes up about one third of the total mass of the asteroid belt. Ceres has a mass of about 1.3% of our moon. So the asteroid belt in total has a mass of roughly 4% of the moon. That is obviously not enough to make a planet similar to Earth or even Mars. And the asteroid belt is too far spread out and has too little mass to ever clump together to form a single body. Ceres is considered a dwarf planet, but it hasn't cleared its orbit, so it can't be called a planet in t he same way that Earth or Mars, etc. can. Another reason why the asteroid belt will not form a planet is Jupiter. Jupiter has such a big influence, it has flung a lot of asteroids out of their orbit, e.g. Kirkwood Gaps. |
Why is lead so much more abundant than gold? | Lead stable isotopes are near a closed nuclear shell. That makes their production in stars much more likely. Also, all of those heavy actinides decay down into lead. So even if it was produced at the same rate in stars as gold was, it will still have more due to the decay of actinides and other heavy nuclei. |
Why does squinting improve my far vision? | This question has [come up before](_URL_0_). To sum up, there are two effects people cite: (1) that squinting changes the shape of your lens and (2) that squinting lets your eyelids/eyelashes act as a pinhole to screen out stray light. |
What are we sensing when we register a metallic taste? Can metals actually have a flavour? | This reminded me of an article I read about the origin of the metallic smell [Nature summary](_URL_1_) , [Journal article](_URL_0_) Basically, that distinctive coin 'smell' is actually the smell of organic molecules from your skin (and anyone else's!) that react with the metal. The last paragraph of the Nature article says that a similar effect may occur when you have a piece of metal in your mouth. |
What is "Metallic" taste? | When you touch iron or copper (and to a lesser extent zinc and some other metals) and then smell or taste metal on your hands, you're sensing a chemical called [1-octen-3-one](_URL_2_). The role of 1-octen-3-one in the taste of metal was only determined recently (2006). Full paper: _URL_1_ This chemical is formed by "skin lipid peroxide reduction and decomposition by low valence metal ions". So you're not tasting metal but a chemical formed from human skin oils/sweat in the presence of metal. It's theorised that this smell is related to our ability to smell blood which forms the same chemical in contact with skin. However... Tasting metal is a common symptom which may be caused by colds, dental problems, nutrient deficiencies, problems with medication or a large range of conditions that cause distortions in your sense of taste: _URL_0_ |
A cube is to a tesseract as sphere is to a _____? What is the four-dimensional model of a sphere? | anything higher than n=2 and they're just generally called n-spheres (with n=2 being our usual 3-dimensional sphere). However a 3-sphere is called a [glome](_URL_0_) |
Is there a 4 dimensional analog to a sphere like a tesseract is for a cube? | Yes, the sphere *S*^(3), which is the *three-dimensional* sphere (embedded in Euclidean four-dimensional space), is the set of points (*x**_1_*, *x**_2_*, *x**_3_*, *x**_4_*) such that *x**_1_*^2 + *x**_2_*^2 + *x**_3_*^2 + *x**_4_*^2 = 1 Similarly for higher number of dimensions. |
Is there any plant that can grow on mars | From [wiki](_URL_0_) "Actual temperature measurements from the Viking landers range from −17.2 °C (1.0 °F) to −107 °C (−161 °F)." Which suggests that it very rarely makes it above zero. I'm guessing the answer is therefore no. But it would be interesting to know whether, if placed in a "greenhouse" like structure, possibly with heating, could earth's plants survive in the atmosphere of mars? (and therefore be able to produce oxygen for us to live) |
Was there an evolutionary advantage to different hair colors in humans? | They probably didn't. It was more likely either sexual selection, or a series of genes that assisted survival with different hair colors as a side effect. Check out how domestic foxes changed when bred for tameness. The behaviors for tameness came with loads of phenotypical changes that were neither bred for nor expected. So different hair color could have been something like that. |
How could a gun fire in space? | All various chemical formulas that we refer to as "gunpowder" all have oxygen atoms as part of their molecule, which is what would allow it to burn in space. There's no air inside a brass casing (it's packed pretty tightly with powder and primer), but the powder still burns, so there's no reason it wouldn't burn in space. |
How does bleach work? | The main mechanism of action is not its acidity or basicity, but it's oxidative power. |
How does bleach work? | Dyes and pigments are usually organic compounds, including those in clothing and hair. These compounds often have a part that is responsible for reflecting the wavelength of light corresponding to its color, this is called the chromophore. There are two types of bleach: - Oxidizing: Contains chlorine, basically destroys the bonds that make up the chromophore, or creates a new chromophore that reflects a wavelength that isn't visible to the naked eye. - Reducing: Contains sulfur dioxide, converts any double bonds in chromophores into single bonds. This changes the structure of the chromophore and changes the wavelength of light its able to reflect. Hope that helps. |
Why do I always get attacked by the shower curtain? | One of the funny things about fluid mechanics is that, for these kinds of complex systems, it is frustratingly hard to get a definitive answer. People have studied this problem, and as far as I know it has not been conclusively answered. The "cause" of the shower curtain sucking inwards is trivial - the air pressure inside is lower than the outside pressure at some point on the curtain. Several mechanisms could possibly explain this. The Bernoulli effect would imply that the high velocity of water coming from the showerhead lowers the pressure inside. Also, the hot steam rising out of the shower could suck air under the bottom of the curtain, and it would be pulled inward due to boundary layer effects. [There is actually a pretty decent wikipedia article on all the various theories](_URL_0_). |
Why are planetary rings not all around planets and instead just form a like like Saturn? | Rings are expected to be short-living: Over time their material agglomerates to moons. To have rings a planet needs something that constantly refills them or it had to have some collision in the recent past. Things don't just randomly enter orbits around other things. If an object is not bound to a planet and approaches that planet it will either impact the planet or fly away again unless something slows it down enough to enter orbit. |
Is baldness in males really passed down from your mother's father? | One type of male pattern baldness is sex-linked, affecting the X chromosome. Females have two X chromosomes and males have an X and a Y chromosome. If mother's father had male pattern baldness, then your mother has at least one copy of a defective X chromosome, giving you a 50% chance of being bald. If your father's father had male pattern baldness, the Y chromosome that gets passed to your father is unaffected. This is only for male pattern baldness, but it accounts for most of the balding that occurs. |
Why does staring at a bright light help me sneeze? | This is known as the [photic sneeze reflex](_URL_0_), and it occurs in about a quarter of people. However, the reason for it is not currently well understood - the linked article discusses a few of the current theories. |
If one cask of wine, or other aged spirit were to be constantly agitated over the course of it's aging, how would it differ from a normally aged cask, if at all? | The reactions that occur while barrel ageing liquor are extremely slow - it takes on the order of 8 to 12 years to got 90-95% conversion of the cogeners. Agitating the cask would speed the process slightly, as it would constantly refresh the fluid near the barrel walls, but given that mass transfer is clearly not the rate limiting step (given the time scales at play), the difference is likely negligible. |
Do animals suffer from mental illness the same way humans do? Can a dog have schizophrenia? | Animal models of mental illness are commonly used in research. It's certainly possible to provoke some of the observable signs in an animal. (Indeed, part of testing novel antidepressants is being really mean to mice.) Pathological behaviors are also noticed in healthy animals, suggesting that something's mentally wrong. Unfortunately, there's no way to diagnose an animal with mental illness, because all we have is observable signs, rather than subjective symptoms. (For that matter, we actually can't confirm whether dogs have migraines.) Dogs can't tell us what's on their minds. It's reasonable to think that similar mechanisms to human mental illness might be at play, but we don't know how animals think. |
Why are red and blue wavelengths of light most useful to photosynthesis? | Look [here](_URL_0_) Notice how on the left side of the total absorption graph everything is absorbed? If you are a plant, you don't want to be absorbing things in that region... so violet is less efficient than things to the right of it. |
do all life supporting planets have a similar ratio of the distance from their nearest star to the size of that star as that of Earth? | Well, right now we know of one life supporting planet: Earth. There is a region called a [habitable zone](_URL_0_) around a star in which water can remain liquid. Because bigger stars are hotter, objects have to be farther away from them in order to be cool enough. So, where this region is depends on how big the star is, but it's not necessarily linear. [This diagram](_URL_1_) from that page gives you a sense of how it changes with mass. Whether water is necessary for life is a different discussion. |
Is there a limit to how small a star can be? If so, what is the theoretically smallest star possible and why? | About 80 times the mass of Jupiter. Below that, they don't have enough mass to get the intense heat and pressure in the core required to fuse hydrogen. These objects are called "brown dwarfs", and generally look more like ~~a enormous~~ Jupiter than a star. The line between a small brown dwarf and a large gas giant is actually a bit fuzzy. |
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