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| Thread ID: 142719 | 2016-08-26 23:48:00 | Super Heat Lamps for instant Warmth? | kahawai chaser (3545) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 1425028 | 2016-09-01 08:11:00 | I refer once more to the Montgolfier brothers and all hot-air balloonists since. Hot-air balloons do not rely on cold air to push them up. However, gravity does play a part, because hot air expands and therefore is lighter than the equivalent volume of cold air, consequently it heads for the ceiling or the clouds. Similarly, ice floats because it has greater volume for its weight, and not just because it because it displaces warmer water. My chimney is a very good example of why your theory must fail. Cheers Billy 8-{) Ah, but what about on Mondays? Everything goes up the Khyber backwards on Mondays. ;) |
R2x1 (4628) | ||
| 1425029 | 2016-09-01 20:33:00 | Actually Billy that's exactly how hot air balloons actually work. The lower density hot air doesn't pull the ballon up, it is pushed by the higher density cold air and it's gravity doing the work. In any case the mechanism doesn't matter, hot air still rises and heat energy still transfers from hot to cold. These 2 properties often work against each other but effectively mean the warmer layer of air at the top of the room will help to warm the lower part of the room over time, the heat is not trapped up there. |
dugimodo (138) | ||
| 1425030 | 2016-09-01 20:42:00 | Actually Billy that's exactly how hot air balloons actually work. The lower density hot air doesn't pull the ballon up, it is pushed by the higher density cold air and it's gravity doing the work. . Gravity? Gravity is a force exerted by an object that pulls the thing down towards it. In a balloon, you're nearer earth than any other space body so I'd say gravity is overcome. |
pctek (84) | ||
| 1425031 | 2016-09-01 21:24:00 | No pctek it is not. Consider 2 balloons full of the same amount of air at 2 different temperatures sitting on the moon. Neither will rise and both will sit happily on the surface. Why? because there is no air pressure to force them upwards and gravity only works towards the centre of the mass right? But what creates air pressure on earth? gravity does by pulling the atmosphere towards the centre and squashing it. The air pressure equalises until it exerts uniform pressure at uniform density in every direction at any given altitude. That pressure also acts upwards (every direction). If you are carrying something and you put it down do you float up into the sky because you are now lighter? of course not. So why does something lighter than air travel upwards when gravity is pulling it down still? Because the force per cubic centimetre acting downwards on the gas all around it is greater than it is in that area of lower density so the upward pressure of the surrounding gas becomes greater than the downward pressure of gravity and the object is pushed upwards, but all of the energy in this equation comes from gravity initially. It's simple in practice but difficult to explain clearly. An analogy is a simple set of scales, gravity pulls down on both ends of the scale but the lighter object is forced upwards by the greater force on the heavier one. Gravity in this case supplies the energy to push the lighter object upwards. In the case of gas there is no physical lever and fulcrum to transfer the energy, it is instead transferred by atmospheric pressure but it's still gravity supplying the force to push the balloon upwards. |
dugimodo (138) | ||
| 1425032 | 2016-09-01 22:34:00 | If you are carrying something and you put it down do you float up into the sky because you are now lighter? of course not. So why does something lighter than air travel upwards when gravity is pulling it down still? Because the force per cubic centimetre acting downwards on the gas all around it is greater than it is in that area of lower density so the upward pressure of the surrounding gas becomes greater than the downward pressure of gravity and the object is pushed upwards, but all of the energy in this equation comes from gravity initially. It's simple in practice but difficult to explain clearly. . still doesnt seem right :) imagine your ballon is shaped like a very thin flat plate . the air pressure above will be the same as the air pressure below it, so it shouldnt float up if it was air pressure causing it it rise up. ? also, unequal weight objects dropped in a vacuum will land at the same time(the great example was feather & hammer on the moon) inertia/gravity nicely balancing so why, does one side of the your scales drop down ? and why does the moon pull the ocean towards it . If anything, in the presence of the moons gravity, in a water/earth system the water should float & the earth be pulled towards the moon (the oceans floating up away from the moon) Im not a flat earther, honest |
1101 (13337) | ||
| 1425033 | 2016-09-02 02:40:00 | The shape of the object doesn't matter, it's just about relative density compared to air. Because the object takes up more space than the equivalent weight of air would air is forced into the space it occupies by the surrounding pressure in all directions and the object is forced upwards towards the altitude where air density matches it and the pressure is equal. You know the scales work, but you don't know why?. It's easy, the downward force of each object pushes the lever down and because one side is heavier it exerts a greater force on the lever and forces the other side to rise. This is what's happening with the balloon as well, the air is denser so has a greater amount of downward force exerted on it for the same amount of volume so it displaces the lighter object. Same reason things float, once you displace the equivalent amount of water to equal the weight of an object it will stop sinking because to go any lower would raise an amount of water heavier than the object. Put it another way, if an object is lighter than air would be if it occupied the same space then air will be pulled into the space it occupies by gravity and that will force the object upwards. This only happens with gases and liquids of course, solids all just fall down and stay there if there is no liquid or gas around to muck things up. The earth and the moon do pull each other and there is a tide in the ground as well as in the sea, we just don't notice it. Because water is more able to move freely it has a more noticeable effect. Again it's not what you might think, the moon does not have the strength to pull anything away from the earth, it's gravity is much weaker and much farther away. What it does do is very slighty reduce the weight of the water beneath it and the the rest of the ocean which is still experiencing the normal weight of water pushes water into the area until the weight equalises and causes a bulge. |
dugimodo (138) | ||
| 1425034 | 2016-09-02 04:07:00 | "Cold air falling down" is also the best way to understand how shower domes work People say "Where does the steam go? Does it condense on the underside of the dome and drip on you?" The answer is that "steam" doesn't get generated in the first place. Clouds of vapour are generated by cold air falling into the shower from above. If you block this off, the clouds don't form. (A bit is caused by air entering the Plaster Ejection Slot) |
BBCmicro (15761) | ||
| 1425035 | 2016-09-02 09:49:00 | For those of you following this Thread, Google "Convection: and "Convectional Currents". There’s a lot of stuff that takes the principal past heating a room. ;) “The transfer of heat through a fluid (liquid or gas) caused by molecular motion seems to be a factor. :D |
B.M. (505) | ||
| 1425036 | 2016-09-07 22:20:00 | interesting, think basically talking about a mix of Newton's laws and the Entropy (randomness) effect. Anyway, decided to keep it simple and relatively cheap by using convectional heater and ventilation...otherwise might end up creating a sauna or similar. | kahawai chaser (3545) | ||
| 1425037 | 2016-09-07 23:07:00 | You know the scales work, but you don't know why?. It's easy, the downward force of each object pushes the lever down and because one side is heavier it exerts a greater force on the lever and forces the other side to rise. yes , I get the basic force is m1.m2.g/d.d (distance squared) and therefore heavier mass has more force on it , but as with the famous moon/astronaut experiment : a feather & hammer dropped will hit the ground at the same time . so heavier objects greater force has to overcome it greater inertia , equalling them out . www.youtube.com now , with that 2 objects dropped experiment above..hammer & feather put a scale underneath them instead , same force, same interia to overcome, but now only the heavier object drops . no scale, they drop/accelerate/fall equally . Add a scale, they dont drop equally Perhaps this is proof we never went to the moon . I shouldnt say that, some will it that seriously :) What it does do is very slighty reduce the weight of the water beneath it and the the rest of the ocean which is still experiencing the normal weight of water pushes water into the area until the weight equalises and causes a bulge. thats a really good explanation , thanks :-) theres also a tide on the other side caused by centrifugal forces , as earth/moon rotate around a common CG |
1101 (13337) | ||
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