I know it's probably the most stupid question there is, but why do they fly are the clouds lighter than air? What's keeping those tiny ice structures floating miles about the ground? I've been looking all over the internet and I can't find acceptable answer to this basic physical question. Can you please help me?  This question was marked as answered - but I don't believe it has been explained satisfactory. Please bare with me on this one.
26501
Clouds are made up of tiny water or ice droplets, depending on temperature. This implies that cloud density is greater than that of dry air. Why don't clouds sink through their surrounding atmosphere rather than float by in a variety of formations?
112332
Alright, so we have all seen the movies where someone gets blasted out of the airlock on their starship, or their suit decompresses while on a space walk. The poor schmoe usually either decompresses so violently that blood is oozing out of every orifice in their body, or they freeze instantly.  From this I have two questions:   Would the decompression really be that violent?   Clearly the drastic difference in pressure from a normal "earth" like environment to space would be bad, but would it be that devastating. I vaguely remember that standard atmospheric pressure was something like 15 psi, which doesn't seem like enough to mess you up that bad.  Would you actually freeze instantly in space?   Heat, or lack thereof is a measure of internal energy, but in a vacuum there wouldn't be anything to have internal energy, so does space even have a temperature? Wouldn't some form of matter have to be present in order to cool off? If there were no matter besides yourself and a few stray particles here and there, it seems like it would take a very long time to cool off.
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I realised, reading another Phys.SE question about  that I don't really understand how  works. Particularly concerning, for a SCUBA diver.  The top answers to that question seem to claim that balloons get their "sense of down" from a pressure differential. They continue: when a car accelerates, the air at the back of the car becomes more dense, and at the front less dense, changing the plane of the pressure differential and so also, the balloon's sense of up. I find that extremely hard to credit. However, I realised that I don't really know why less dense things float in more dense things.  I'm fairly sure it's something to do with displacement of heavier things by lighter things, and I think pressure acting on the lighter thing's surface has something to do with it, but that's about it.
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There is a  being thrown out of a flask, literally hovering out of the container  My question is how detailed a physical explanation of this phenomenon we have?  Question: More precisely, if we used the best available mechanical physics simulator software, and we tried to simulate this behavior, would the software be able to reproduce the effect or not? My guess is not but I would like to know why not.  Or do we have to content ourselves only with handwaved explanations? I am from the school of thought that you don't understand physics until you have a reasonable certainty that you can reproduce the physics in a computer.
31480
This is a strange question I would like to have some explanation accompanied with:  We have an ice block, with in it a lead block. This entire block is put into a glass of water, resulting in a rise of water level until the edge of the glass. The block stays floating on the surface. What will happen with the water level when the ice melts?  The answer is that it will drop, but how is this even true?? My thoughts are: - block floats on water, so rho(block) &lt; rho(water) - Archimedes law, the Fg of block = Fg of water pushed away. - Since a smaller volume of water has equal mass (and so Fg) to block, and ice is less dense than water, when it melts, no mass is lost, so it will take in less space??? Please help me with this point of thinking.
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Pretty simple question, but not an obvious answer at least not to me.  I mean you can't just place a dead fly on the wall and expect it to stay there, he will fall off due to gravity.  At first I thought it maybe friction, but that would require a normal force (i.e. perpendicular to the wall), and then I remembered spiders, geckos etc, they like to walk around on the ceiling.    How is it possible?  What kind of forces are involved?  Would these creatures still be able to do it on a hypothetical surface which was perfectly flat?
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Yesterday my friends and I were solving this easy-looking question:  A metal cube is placed in an empty vessel. When water is filled in the vessel  so that the cube is completely immersed in the water, the force on the bottom of the vessel in contact with the cube: (A) Will Increase (B) Will Decrease (C) Will remain the same (D) Will become zero  At first we thought the answer to be (B) considering the buoyant force acting opposite to the weight of the cube. But then, a question popped up in my mind: &quot;What causes this buoyant force even if no fluid was actually displaced?&quot; So I referred to the Archimedes' Statement:  Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. — Archimedes of Syracuse  But according to the question, no such fluid was displaced by the block ! So, here are my questions:  What is the basic reason behind buoyancy? Is it the pressure difference in fluids or the 'liquid-displaced' theory?  What must be the answer to the question (That I was solving) ?  Considering the case that you may say- &quot;The reason behind buoyancy is the pressure difference in the fluids&quot;; Will there be no buoyant force applied to the iron cube as there is no fluid layer present below the cube i.e. no pressure difference?   (Considering the iron cube is VERY dense and thus not allowing any fluid layer to push its way below it)  Or you might add another statement to the above question that-&quot;Yes, buoyant force is applied as there is always a fluid layer present below it...&quot; .Please do explain yourself.  If your answer is according to the Principle given by Archimedes of Syracuse , will there be no buoyant force on the cube as the cube didn't actually displace any fluid? Just like the case where you may consider it to be a part of the vessel itself.
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There exists this famous idea that if all floating icebergs melt, water level will stay the same (because the water replaced by ice is the volume of the melted ice). Now,   Is this always so, if you allow more exotic forms of ice (take e.g. ice XII with density 1.29) ? Is this always so on/in earth ?   EDIT:  I was looking a possibility that you would have water as a liquid that contains pieces of water as a solid. No land is assumed to exist here. "Ice" is always floating or sunken(if possible).  To reformulate, can Ice be sunken in water in any circumstance (pressure, temperature)?  EDIT 2:  Wikipedia: "Ice VII has a density of about 1.65 g cm-3 (at 2.5 GPa and 25°C)".   And water as an incompressible liquid has a density of 1 g cm-3. This means that ice VII is at the bottom of the "lake" and will expand when it melts. Is this true? And are there environments in earth where this (or similar) can happen?
33727
What causes the surface of the lake to appear darker in some places?   Firstly, I know that it's not fishes that cause it. Secondly, the dark surfaces move from time to time and thus are not associated with the depth of the water or the structure of the lake bottom. Lastly, I may say they are due to a kind of ripple distortion. What causes this distortion and what is its mechanism?  Please, provide more explanation than "the wind", for example.  In this photo, look at the far area; it's darker somehow.
12453
What aerodynamic effects actually contribute to producing the lift on an airplane?  I know there's a common belief that lift comes from the Bernoulli effect, where air moving over the wings is at reduced pressure because it's forced to travel further than air flowing under the wings. But I also know that this is wrong, or at best a minor contribution to the actual lift. The thing is, none of the many sources I've seen that discredit the Bernoulli effect explain what's actually going on, so I'm left wondering. Why do airplanes actually fly? Is this something that can be explained or summarized at a level appropriate for someone who isn't trained in fluid dynamics?  (Links to further reading for more detail would also be much appreciated)
103101
I guess it's not a very educated question, but I never quite understood why spacecrafts have to shoot up and can't just reach space by simply continuing an upwards ascent like an airplane.
61704
I have a hard time understanding whether or not a wing placed in a potential flow, assuming there is no viscosity and no friction with the wing, will produce a lift. I've seen several contradictory (to me) versions of what happens in this case, in particular:   In Landau - Lifshitz, Vol 6, §11 it is shown that the force vector on any object in a potential flow is zero (i.e. there is neither lift nor drag). The mathematics behind this derivation are above my understanding, thus I can't really follow how this is shown and what assumptions are made along the way. The Wikipedia article on the  states that a body in a potential flow does not experience drag. On the other hand the article does not say anything about lift forces and the German version explicitly states that it does not apply for lift forces. A common explanation for the lift produced by wings seems to be that its asymmetric shape causes a higher velocity of the flow above the wing and a lower below. Due to Bernoulli's equation that would result in a pressure-difference and thus a force. Honestly I don't quite get this explanation as I don't see where the different velocities are supposed to come from (without friction and thus without the circulation resulting from turbulences behind the wing).   So now I'm wondering, do or do not wings have lift in irrotational, inviscid, incompressible fluids.
114308
Is there a specific speed that Summoned objects fly at, and if so, what is it? If not, how is speed determined?
112054
This can happen during the rain, or when pouring water. Sometimes small (1-2 mm) droplets of water float on the surface for some time (a few seconds) before coalescing with the big body of water. A very refined example of this phenomenon is  experiment, captured by a high-speed video camera.   study explores it in detail, but the explanation for this behavior seems implicit.  So how can this behavior exist at all? I imagine that the forces of gravity and surface tension act on the droplet in the same direction; so what supports it from below (or even makes it bounce, like in the video)? Is it the trapped air that escapes very slowly to the sides? If yes, why is it so slow?
5139
SPOILERS FOR   Star Trek Discovery Season 1 Episode 3       The Shuttle that Michael Burnham is on is flying through a dangerous cloud that has energy-eating organisms inside it. When the discovery rescues the ship you see it just outside the cloud above the shuttle clearly is not in danger. So the question is: Why did the shuttle fly through the cloud when it clearly could have flown above the cloud?
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The machines turned to using humans as a source of power after the humans darkened the skies, since the machines relied on solar power before.  If the machines were smart at all, they'd realise that their strategy is unsustainable, since energy on Earth predominantly comes from the Sun in some shape or form (i.e. plants, oil, coal). So why would they not invest into penetrating or even getting rid of the clouds?  The 3rd movie clearly shows that it's possible to penetrate the cloud layer when Trinity flies through it. Although there was an issue with the lightning interference, hey, they survived! And I'm sure they can either build some sort of shielding, or even harness the lightning to their advantage.
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In the movies, the Death Eaters leave a smoky trail behind them as they fly. As the Order arrive in the Ministry of Magic in Order of the Phoenix, they leave a silvery trail behind them. In the books, there’s no mention of how they’re doing this. And J.K. Rowling said in the books that only Voldemort and Snape could fly like this; first seen in the Battle of the Seven Potters.  Please can somebody explain how the Death Eaters are able to fly like this?