물은 공기보다 768배 무겁다

물은 공기보다 768배 무겁다 (Do you) Still have a question? Ask your own! What is your question? Water is 780 times heavier than air. How do massive amounts of water stay floating in the sky as clouds? Kim Aaron, Has PhD in fluid dynamics from Caltech Answered May 2, 2016 Originally Answered: How can a cloud float in the sky, if it weighs around 1.1 million pounds? Clouds do not float in the sense of being buoyant. A cloud is made of bajillions of tiny tiny water droplets. They are gradually falling through the air, but very very slowly. Any updraft is able to carry them upward faster than they are falling down. Also, at the edges of clouds, as moist air blows in to the cloud, new water droplets condense, and as droplets blow out, they vaporize. A cloud can appear to be stationary despite wind blowing in the region of the cloud. Following the edge of a cloud is not a good indication of the wind speed there. If you watch time lapse video of clouds, you will get a better feel for all the roiling that is going on as well as see that a cloud is not all the same water. Here's on example: Your response is private. Are you satisfied with this answer? Shubhayu Chatterjee, Physics student Answered Jul 17, 2013 As already mentioned by Eric Pepke, updrafts of rising air provide a lift to the water droplets that counteracts their weight. When quite a few water-droplets coalesce to form a big one, its surface area decreases, the reason being surface tension of water. So it cannot be kept up by air drafts, and it falls down as rain. A way to visualize this is to think of a cloud as essentially an Aerosol, a suspension of liquid particles floating in air. Think about dust particles - they are heavier than air if they are lumped together, yet they can float in air if they are appropriately dispersed in the media. A similar thing happens for water droplets in the cloud. They would fall down, but they keep receiving kicks from the air molecules. Because warmer air rises up from the earth surface, the average net force on the water droplets is directed upward. As long as this force can balance gravity, water molecules remain afloat. This is what happens for the smaller droplets. The larger ones have less surface area, and the upward force no longer balances gravity. Hence, they fall as rain. · 16 Upvotes · Answer requested by Darshan Singh Answered Sep 9, 2014 Here's a weird twist: water is lighter than air. At least, a water molecule is lighter than an average air molecule, which means that water vapor (18 g/mol) is lighter than air (29 g/mol). On the other hand, that doesn't really matter, because water mixes with the air too much to really float or sink, it just spreads and spreads, so you have tons of water vapor in the air, both near the ground and higher up. Now, when the vapor condenses into liquid, it gets more complicated. You're right that liquid water is more dense than air, and that's why it rains. But very, very small droplets of water are too light to fall, at least at any appreciable rate. Gravity tries to pull the droplets down, but air resistance tries to slow that process down. When drops get below a certain size, they have so little weight that they can't overcome the air resistence, and effectively stop falling. It's a similar effect to why dust particles seem to be able to float forever without falling. Eventually, the droplets either coalesce into bigger drops and fall as rain, or they break up and turn back into vapor. But that can take a long time, and until then, they just drift in the movement of the air. Chris Riley, Middle School Science Teacher Answered Mar 4, 2015 Originally Answered: How do clouds float? Air has water vapor in it. Sometimes more, sometimes lessWarm air can hold more water vapor than cold airWarm air is less dense than cold air, so it floats above it. It is less dense because the air molecules have more energy and bounce against each other harder, spreading out a bitAs the air rises, it spreads out and this cools the airEventually, the air cools enough that it can't hold all the water vapor it has. This water vapor condenses into tiny droplets of liquid water. This creates cloudsSo, clouds come from air cooling down below the critical temperature that make the water vapor condense. This temperature is called the dew point. The dew point is different depending on how much water vapor the air hasCumulus clouds (fluffy, piled up clouds) are made from rising air. Shawn has already pointed out that cumulus clouds indicate where warm air is rising (thermals)While clouds are heavy, they are also very large. They have a very low density. Eventually, the droplets have grown large enough that the air can't hold them up anymore. This causes rain. Steve Harris, Scuba enthusiast Answered Sep 29, 2016 Continue Reading Here’s the deal: standard cumulus clouds are made of very tiny (cell-sized) droplets of water, which are small enough to float in updrafts, like dust. If you want to quantitate it, water is perhaps 800 times as dense as air, but a cloud has distances between droplets (roughly 1 mm = 1/25th inch) that are 100 times the size of the droplets themselves (which average very roughly 1/100 mm, or about the average size of cells in your body). Which means a cloud has 100 x 100 x 100 or a million times more air volume than water volume. Take the average of the two densities, and you find a good fluffy cumulus cloud might be only 1.0004 times the density of dry air. Instead of being 1400 grams per cubic meter (density of dry air), it’s half a gram over that, and the extra half gram per cubic meter, is water. By weight, a cloud has ~ 3000 times more air than water. The extra weight is small enough to be pushed up by up-going thermals, like a big balloon that is just slightly more dense than air, and is trying to settle. Still, a good-sized cloud, even containing half a gram water per m^3 (again, the other 1400 grams being air), might easily contain a million lbs (500 tons) of water. This is how much a cloud weighs For the cloud to rise, thermals must be pushing it upward with a force of 500 tons! 552 Views · 7 Upvotes · Answer requested by Yazed ALNemer Upvote · 7 Comment... RecommendedAll Todd Gardiner, Photographer and questioner of too much privacy Answered Jul 17, 2013 Continue Reading Clouds are weird cyclic things, converting back and forth from invisible water vapor and visible droplets of liquid water. As the water droplets descend, they reach warmer air and turn back into water vapor, which rises. As it rises, it becomes colder and eventually turns back into water droplets. The whole mass is held aloft by the pressure of updrafts of air and water vapor rising from the ground. Sunlight causes evaporation of surface moisture, like dew or standing water. Areas that become too dense with water droplets/vapor end up losing some of that water as rain. There are also factors having to do with local air pressure and atmospheric temperature gradients, but this is getting into a a complicated area of meteorology. The transition back and forth between liquid water and water vapor at higher altitudes is aided by the fact that the low air pressure reduces the boiling temperature. At 40,000 ft. its only 135ºF (57.5ºC). The amount of sunlight that needs to be absorbed or energy absorbed from the atmosphere is reduced, compared to sea level. Remember that boiling point is the temperature at which ALL of a liquid undergoes phase change to gas. At lower temperatures, there is partial evaporation, particularly when you have other energy sources, like sunlight, which can energize individual surface molecules. This is what drives clouds in their evaporation/condensation cycle. (from Wikimedia Commons) 1.2k Views · 4 Upvotes Upvote · 4 Comment... RecommendedAll Eric Pepke, Recovering Mad Scientist Answered Jul 17, 2013 Continue Reading It doesn't. It rains. It says up for a while because the droplets are very small, and so they have a lot of surface area compared to their mass. There's a lot of resistance to falling, because of this, and updrafts keep them up. Also, clouds condense out of water vapor from the cold. If they come down a bit and warm, they turn into steam again and go right back up. But when they get too big, down they come. 2.7k Views · 14 Upvotes Upvote · 14 Malcolm Sargeant Clouds don't float in the sky they form up there and eventually come down. Tim Garrett, Professor of Atmospheric Sciences (2002-present) Answered Aug 26 Continue Reading Originally Answered: How are clouds floating? It’s a bit misleading to think about a cloud as a fixed object since they are constantly forming and dissipating, only creating the illusion of the fixed object because our attention spans are too short to watch them evolve. When water vapor in clear air condenses it creates a visible cloud and releases energy called latent heat that makes the cloud air warmer than surrounding clear air. This is the primary means by which cloudy air maintains its buoyancy so that it can rise. 44 Views Upvote Comment... RecommendedAll Shawn McCaslin Answered Mar 3, 2015 Continue Reading Originally Answered: How do clouds float? Clouds are tracers of atmospheric conditions. Clouds indicate areas of the atmosphere where the air temperature is lower than the dew point. Air density is not affected by the formation of clouds, so clouds are not really floating. Cumulus clouds show where blobs of hot air have risen rapidly due to convection into higher areas of the atmosphere. So, for example, if you were a glider pilot, you would look for cumulus clouds to indicate where rising air could provide lift. Since that lift is localized, the boundary between the rising air and more stable air can be turbulent. Indeed, while clouds frequently appear to be remarkably localized (why aren't they more rapidly dissipated by diffusion?), they are really the 'tip of the iceberg'. Through entrainment, air that rises due to convection pulls more air along with it, that is also likely hot and humid. Condensation releases considerable heat, increasing the lifting power of the convection cells. You can see how this process would drive the formation of thunderstorms, which arereally strong sources of turbulence. 696 Views · 2 Upvotes Upvote · 2 Comment... RecommendedAll Nazirite Ssembajwe Ronald, theoretical physicist Answered May 19, 2016 Continue Reading Originally Answered: How do clouds float? Okay. Disclaimer: my answer is just [sic] from the same question at Y!A. Clouds are formed when the air is lifted by a lifting mechanism such as a cold front or when the air becomes positively buoyant (think of a helium filled balloon). As the air rises it cools and any moisture (water droplets) that are available will condense into cloud droplets. It is important to remember that clouds tend to have more moisture than the air surrounding them. Water vapor is lighter than diatomic Nitrogen or Oxygen, therefore the cloud will have a tendency to float on the drier air underneath it. Also, the movement of air around and in the cloud will keep the tiny particles within the cloud to stay suspended. Think of a feather falling to the surface, it falls much slower than a coin or a ball would because it is very light and the movement of air tries to keep it suspended. 279 Views · 2 Upvotes · Answer requested by Yazed ALNemer and Rashid Winter Upvote · 2 Comment... RecommendedAll Rakesh Teja Konduru, worked at Research Fellow Answered Mar 8, 2015 Continue Reading Originally Answered: How do clouds float? First of all, “moist air” is air with a high water vapour content. Water vapour, the invisible, gaseous form of water, occurs in highly variable amounts in the atmosphere. Water is composed of a hydrogen atom and two oxygen atoms (H2O) and has a molecular weight of 18 grams per mole. (One mole of a gas, at standard conditions, has a volume of 22.4 litres.) “Dry” air contains no water vapour, and is mostly a mixture of molecular nitrogen (N2) and molecular oxygen (O2). The molecular weight of dry air is 28.97 grams per mole. This cases moist air lighter than dry sir. Since clouds are made up of moist air, hence they floats on dry air. 440 Views ·