Robin-H Posted March 27, 2018 Share Posted March 27, 2018 OK, so the balloon still has a weight which must be overcome by some force which is called buoyancy. My question is: what are the mechanics that explain buoyancy? You want the Archimedes principles behind buoyancy? The equation? Link to comment Share on other sites More sharing options...
barleycorn Posted March 27, 2018 Share Posted March 27, 2018 OK, so the balloon still has a weight which must be overcome by some force which is called buoyancy. My question is: what are the mechanics that explain buoyancy? If this still holds true then you already know the answer. This one has really got me puzzled. I am aware of the Archimedes Principle & can see how it applies to liquids, but I cannot see how it accounts for, say, a helium-filled balloon rising. Such a balloon still has mass & will accelerate upwards when released. If a mass accelerates, a force must be acting on it. My question is: where does this force come from? I await the deluge of suggestions (sensible or silly). "Every object is buoyed upwards by a force equal to the weight of the fluid the object displaces." Remember a gas is a fluid... Link to comment Share on other sites More sharing options...
fatrajah Posted March 27, 2018 Share Posted March 27, 2018 If this still holds true then you already know the answer. "Every object is buoyed upwards by a force equal to the weight of the fluid the object displaces." Remember a gas is a fluid... The problem I am having is that there supposed to be a difference in pressure between the top half of the balloon & the bottom half of it over such a small distance ie 30 cm. It may well be true but I doubt it could be measured directly. Link to comment Share on other sites More sharing options...
Robin-H Posted March 27, 2018 Share Posted March 27, 2018 The problem I am having is that there supposed to be a difference in pressure between the top half of the balloon & the bottom half of it over such a small distance ie 30 cm. It may well be true but I doubt it could be measured directly. A cork floats in water (and rises until it reaches a point where the surroundings are no longer denser than it). It is the same as a helium balloon floating in air and rising until the surrounding air (which is also a fluid) is no longer denser than it. The size of the object doesn't matter at all. It isn't to do with the difference in pressure between the top half and bottom half of the balloon either. There will be thousands and thousands of sites and explanations of this online pitched for different levels of understanding. I suggest you digest some of them. Link to comment Share on other sites More sharing options...
barleycorn Posted March 27, 2018 Share Posted March 27, 2018 I can be but you don't need to. Buoyancy force = weight of displaced fluid. ---------- Post added 27-03-2018 at 16:57 ---------- A cork floats in water (and rises until it reaches a point where the surroundings are no longer denser than it). It is the same as a helium balloon floating in air and rising until the surrounding air (which is also a fluid) is no longer denser than it. The size of the object doesn't matter at all. It isn't to do with the difference in pressure between the top half and bottom half of the balloon either. There will be thousands and thousands of sites and explanations of this online pitched for different levels of understanding. I suggest you digest some of them. I'm waiting for the gotcha that somehow proves Flat Earth Link to comment Share on other sites More sharing options...
Robin-H Posted March 27, 2018 Share Posted March 27, 2018 I can be but you don't need to. Buoyancy force = weight of displaced fluid. ---------- Post added 27-03-2018 at 16:57 ---------- I'm waiting for the gotcha that somehow proves Flat Earth Yes it does seem to be heading that way. Link to comment Share on other sites More sharing options...
fatrajah Posted March 27, 2018 Share Posted March 27, 2018 A cork floats in water (and rises until it reaches a point where the surroundings are no longer denser than it). It is the same as a helium balloon floating in air and rising until the surrounding air (which is also a fluid) is no longer denser than it. The size of the object doesn't matter at all. It isn't to do with the difference in pressure between the top half and bottom half of the balloon either. There will be thousands and thousands of sites and explanations of this online pitched for different levels of understanding. I suggest you digest some of them. I have looked at some of these sites & they explain buoyancy in liquids in terms of pressure difference. Are you saying that this does not explain buoyancy in gases? BTW I am not a flat-earther etc. Link to comment Share on other sites More sharing options...
stifflersmom Posted March 27, 2018 Share Posted March 27, 2018 A cork floats in water (and rises until it reaches a point where the surroundings are no longer denser than it). It is the same as a helium balloon floating in air and rising until the surrounding air (which is also a fluid) is no longer denser than it. The size of the object doesn't matter at all. It isn't to do with the difference in pressure between the top half and bottom half of the balloon either. There will be thousands and thousands of sites and explanations of this online pitched for different levels of understanding. I suggest you digest some of them. My bold - that isn't quite correct though is it? The bouyancy effect (force) is a direct result of the pressure differential. Link to comment Share on other sites More sharing options...
Robin-H Posted March 27, 2018 Share Posted March 27, 2018 I have looked at some of these sites & they explain buoyancy in liquids in terms of pressure difference. Are you saying that this does not explain buoyancy in gases? BTW I am not a flat-earther etc. Buoyancy is explained in terms of fluids. Both liquids and gases and fluids. Give this a watch. ---------- Post added 27-03-2018 at 17:23 ---------- My bold - that isn't quite correct though is it? The bouyancy effect (force) is a direct result of the pressure differential. Yes you're right, it is do with the pressure differential between the air outside the balloon at the top and air outside the balloon at the bottom (and the differential to the helium inside the balloon). I mistook the comment to mean that balloons rise because the top of the balloon had air of a different pressure in the top half to the bottom half. Link to comment Share on other sites More sharing options...
fatrajah Posted March 27, 2018 Share Posted March 27, 2018 (edited) I have had look at the MIT video & sure enough it's all down to the difference in air pressure above & below the balloon. Just out of interest I did a calculation of the pressure difference over a vertical length of 30 cm. The pressure gradient at low altitude is reckoned to be 1.2KPa per 100 metres. This works out at 0.2358 gm or 231.3198 dynes of upward force for our balloon. Not much is it? Edited March 27, 2018 by fatrajah Link to comment Share on other sites More sharing options...
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