Lorentz Jr Posted January 28, 2023 Share Posted January 28, 2023 (edited) 5 minutes ago, studiot said: So you are claiming that a pure tension structure made of flexible fabric can support compression ? Of course, except I'm treating the high-pressure gas inside the balloon as part of the structure. A rigid object is a kind of structure, a gas-filled balloon is a kind of structure, the rim and spokes of a bicycle wheel are a kind of structure, the spars and stays on a sailboat are a kind of structure, and those funny combinations of hook-shaped thingies that somehow hang together are a kind of structure. The nature of the internal structure and the external forces acting on the structure are separate issues. Edited January 29, 2023 by Lorentz Jr Link to comment Share on other sites More sharing options...
studiot Posted January 29, 2023 Share Posted January 29, 2023 Just now, Lorentz Jr said: Of course, except I'm treating the high-pressure gas inside the balloon as part of the structure. A rigid object is a kind of structure, a gas-filled balloon is a kind of structure, the spars and stays on a sailboat are a kind of structure, and those funny combinations of hook-shaped thingies that somehow hang together are a kind of structure. The nature of the internal structure and the external forces acting on the structure are separate issues. Please give me strength. Go back to the two correct things you said which were 1) The air density inside the balloon is lower than the air density outside. 2) The air pressure inside the balloon is greater than the air pressure outside. ( But - my comment - this cannot be true at the opening or the higher pressure air would simply exit the balloon. This is why the given analysis sets the pressure at the bottom to be equal inside and outside ). Now consider a Montgolfier design; a ball shape with say the bottom 40% cut away to form the hot air entry part. The remaining of the lower hemisphere wiil be curved in such a way as for the higher pressure at the bottom to push down harder on it than the lower pressure pushes upwards further up. At the equator of course the net force is horizontal inside the balloon. Link to comment Share on other sites More sharing options...
Lorentz Jr Posted January 29, 2023 Share Posted January 29, 2023 (edited) 59 minutes ago, studiot said: Please give me strength. I can't give you strength, studiot. I can only help you understand. 59 minutes ago, studiot said: Now consider a Montgolfier design How about we forget about designs, studiot, because they're not really on topic, they're all subject to the same physics, and using big words like "Montgolfier" doesn't prove anything. 59 minutes ago, studiot said: The remaining of the lower hemisphere wiil be curved in such a way as for the higher pressure at the bottom to push down harder on it than the lower pressure pushes upwards further up. That applies to any balloon. Small hole, no hole, whatever. Obviously the total internal force pushing down on the lower part of the balloon has to be greater than the internal force pushing up on the upper part, because the net force of the fabric on the hot air has to support the air's weight. Edited January 29, 2023 by Lorentz Jr Link to comment Share on other sites More sharing options...
Saber Posted January 29, 2023 Author Share Posted January 29, 2023 Whats inside the buckets ? i man under the membranes ? water or air ? 10 hours ago, Genady said: Here is a suggestion to produce perpetual motion using buoyancy. Consider this kind of device submerged in water: It has two wheels with a belt, and cups attached to the belt. I drew two cups on each side, but the belt can be as long as needed and there can be as many cups attached as needed. Each cup is covered with a flexible membrane with weight attached to the center of the membrane. When cup is on the right, the opening faces upward and the weight pushes the membrane inward. When cup is on the left, the opening faces downward and the weight pulls the membrane outward. Thus, the cups on the right have smaller volume than the cups on the left. Consequently, the buoyancy force on the left is greater than on the right, and the device starts rotating clockwise. Each time a cup crosses from left to right over the wheel on top, its membrane moves inward and its volume decreases, but at the same time another cup crosses from right to left under the wheel on bottom, its membrane moves outward and its volume increases. So, the motion continues. We know that something is wrong here, but what? Whats inside the buckets ? i mean under the membranes ? air or water ? Link to comment Share on other sites More sharing options...
Lorentz Jr Posted January 29, 2023 Share Posted January 29, 2023 (edited) 27 minutes ago, Saber said: air or water ? Air. Or a vacuum, if you like. Something light and compressible. Edited January 29, 2023 by Lorentz Jr 1 Link to comment Share on other sites More sharing options...
Saber Posted January 29, 2023 Author Share Posted January 29, 2023 (edited) You know thinking is a little hard in the situation i have ......last night drones came in side my ( Sh*thole ) country and had hit 5 military facilities one near my home about 10Km distance and i think things are gona escalate ........my mind is on survival mode............and i have to force it to think about science..... Let alone the internet is so slow it will grind your gears.......... Trying to concentrate on the topic....... I simplified it like this .......... W= weight of buckets + the weights B = buoyant force of the whole bucket + weigh in the case that the membrane is stretched out and the volume of the bucket is more thus the buoyant force is more b -= Buoyant force of the whole bucket + weigh in the case that the membrane is pushed in..........so the over all volume of the bucket + weight is less thus the buoyant force is less So to simplify it the over all force on the left buckets = W-B lets call it for example A and the one for the right one = W-b and lets call this one for example a but what direction are A & a up or down ? and that depends on .......how much is W ? if W is way much more that the buoyant forces of B and b then the buoyant forces cant cancel it........and so the over all force on both left & right side is downwards and so the system would and could not rotate And if the W is less that the buoyant forces .....and they can cancel W out........again both forces on the R & L would be upwards and again it cant rotate right ? But if B>W>b then the system could probably start to rotate CW right? Edited January 29, 2023 by Saber Link to comment Share on other sites More sharing options...
Lorentz Jr Posted January 29, 2023 Share Posted January 29, 2023 (edited) 57 minutes ago, Saber said: ......last night drones came in side my ( Sh*thole ) country and had hit 5 military facilities What continent? 57 minutes ago, Saber said: ........my mind is on survival mode............and i have to force it to think about science..... Don't forget about survival though. That's important too. 😶 57 minutes ago, Saber said: W= weight of buckets + the weights Assume that W is big enough for the weights on the left side of the belt to hang down, even at the bottom of the belt. 57 minutes ago, Saber said: But if B>W>b then the system could probably start to rotate CW right? The condition for buoyancy is that the weights on the left side hang down. That means [math]W > \rho g DA[/math], where [math]\rho[/math] is the density of water, [math]A[/math] is the cross-sectional area of each cup, and [math]D[/math] is the depth at the bottom of the belt.* The question is, what happens when a cup goes around the top or bottom of the belt? For simplicity, you can assume that something keeps each weight locked in place while it goes around a pulley, and the weight is unlocked when the cup is vertical again. So you don't need to worry about the cup's rotation while it's happening. Only the final result of it being turned upside-down. * (with possible adjustment(s) for atmospheric pressure, depending on what's inside the cup) Edited January 29, 2023 by Lorentz Jr Link to comment Share on other sites More sharing options...
Genady Posted January 29, 2023 Share Posted January 29, 2023 4 hours ago, Lorentz Jr said: What continent? My guess: Iran says drone attack targets defense facility in Isfahan - ABC News (go.com) Link to comment Share on other sites More sharing options...
Saber Posted January 29, 2023 Author Share Posted January 29, 2023 2 hours ago, Lorentz Jr said: What continent? In the cross roads of the old world..............the main conflict ground of human race from the dawn of civilization AKA middle east 2 hours ago, Lorentz Jr said: Don't forget about survival though. That's important too. 😶 You know when your worried & anxious your mind really cant think about the things that are not liked directly to its survival........I mean when did humans evolve mentally and started to build & make tools and then start primitive civilizations ? When they reached to a point that they had enough to eat and had some reliable amount of security i mean when they had enough time + energy + free mind.............. In the region i live....the society has not completely covered up that part of the human social evolution......* unfortunately....... And again unfortunately..........there a thing called the ladder of opportunity........And the ones who climb it first would dismantle the stairs as they are not interested in sharing their higher position with others............ and that principle implies and is present in the natural evolution of the creatures also..........you know this natural world doesnt have that much ethics and morals after all........... Never mind i dont wan to derail this thread and these talks belong to some other topic and forums.......... 3 hours ago, Lorentz Jr said: Assume that W is big enough for the weights on the left side of the belt to hang down, even at the bottom of the belt. The condition for buoyancy is that the weights on the left side hang down. That means W>ρgDA , where ρ is the density of water, A is the cross-sectional area of each cup, and D is the depth at the bottom of the belt.* The question is, what happens when a cup goes around the top or bottom of the belt? For simplicity, you can assume that something keeps each weight locked in place while it goes around a pulley, and the weight is unlocked when the cup is vertical again. So you don't need to worry about the cup's rotation while it's happening. Only the final result of it being turned upside-down. * (with possible adjustment(s) for atmospheric pressure, depending on what's inside the cup) So you mean that W> B or b ? right ? in that case both forces on both sides are downward but the force on the right side is greater as its buoyant force is less but in that case i dont know In that case the forces on the right side is more than the ones on the left side...............and i dont know if they cancel the left forces and then the system would rotate CW or......???? I have to think more to find ou where the .........fishy thing is...................... Link to comment Share on other sites More sharing options...
Genady Posted January 29, 2023 Share Posted January 29, 2023 5 hours ago, Saber said: but what direction are A & a up or down ? As you have defined, A=W-B and a=W-b. This definition means that A and a are directed down. But be careful: if for example B>W then A is negative. What does it mean that negative force, A, is directed down? It means that a positive force, -A, is directed up. However, we can continue to consider down forces A and a knowing that a negative force down means a positive force up. Since B>b, it removes from W on the left more than on the right, and A<a. In other words, the downforce on the left is smaller than the downforce on the right. The balance will make right side to move down and the left side to move up. We can simplify more. Instead of the membranes consider pistons in the cylinders. On the right side, the weight of the piston makes it to go all the way inside the cylinder to its bottom. This cylinder would not experience any buoyancy (ignore the walls thickness), only the weight. On the left side, the weight of the piston makes it to go all the way to the edge of the cylinder (something stops it there). This cylinder would experience the same weight as on the right but also a buoyancy. The weights on the left and on the right cancel and the buoyancy on the left would make the left cylinders to float up. 1 Link to comment Share on other sites More sharing options...
Saber Posted January 29, 2023 Author Share Posted January 29, 2023 (edited) 58 minutes ago, Genady said: As you have defined, A=W-B and a=W-b. This definition means that A and a are directed down. But be careful: if for example B>W then A is negative. What does it mean that negative force, A, is directed down? It means that a positive force, -A, is directed up. However, we can continue to consider down forces A and a knowing that a negative force down means a positive force up. Since B>b, it removes from W on the left more than on the right, and A<a. In other words, the downforce on the left is smaller than the downforce on the right. The balance will make right side to move down and the left side to move up. We can simplify more. Instead of the membranes consider pistons in the cylinders. On the right side, the weight of the piston makes it to go all the way inside the cylinder to its bottom. This cylinder would not experience any buoyancy (ignore the walls thickness), only the weight. On the left side, the weight of the piston makes it to go all the way to the edge of the cylinder (something stops it there). This cylinder would experience the same weight as on the right but also a buoyancy. The weights on the left and on the right cancel and the buoyancy on the left would make the left cylinders to float up. If the buoyant force is more than the W to there would be upward force on the left pistons and downward on the right ones And if the B is less than the W then there would be downward forces on both sides but greater on the right ........ And it seems that in both scenarios the system would rotate CW But still i cant figure out why it would not .....................dont tell it.....give me some time.............i want to see if im intelligent enough to find it out....... Edited January 29, 2023 by Saber Link to comment Share on other sites More sharing options...
Genady Posted January 29, 2023 Share Posted January 29, 2023 13 minutes ago, Saber said: My problem is that i dont know is the buoyant force more that the weight of the pistons or less ? This is a good assumption: 5 hours ago, Lorentz Jr said: Assume that W is big enough for the weights on the left side of the belt to hang down, even at the bottom of the belt. Assume that W=100 ton. 1 Link to comment Share on other sites More sharing options...
Saber Posted January 29, 2023 Author Share Posted January 29, 2023 (edited) 5 minutes ago, Genady said: This is a good assumption: Assume that W=100 ton. Is the tricky part the section that the pistons reach @ the top & bottom ? Edited January 29, 2023 by Saber Link to comment Share on other sites More sharing options...
Lorentz Jr Posted January 29, 2023 Share Posted January 29, 2023 (edited) 1 hour ago, Saber said: Is the tricky part the section that the pistons reach @ the top & bottom ? The tricky part is, what happens to the weights? What effect do they have on the belt when they go up and down? 1 hour ago, Genady said: Assume that W=100 ton ... and D*A < 100,000 liters! 😆 Edited January 29, 2023 by Lorentz Jr 1 Link to comment Share on other sites More sharing options...
Genady Posted January 29, 2023 Share Posted January 29, 2023 (edited) 2 hours ago, Saber said: Is the tricky part the section that the pistons reach @ the top & bottom ? Let's simplify even more. Let's assume that the top wheel is above the surface. Then the cups on top turn from left to right while out of water and it doesn't matter what exactly happens there as there is no buoyancy on either side there anyway. Edited January 29, 2023 by Genady 1 Link to comment Share on other sites More sharing options...
Saber Posted January 30, 2023 Author Share Posted January 30, 2023 These days im soooo busy @ work i im left with no energy to think @ all .............but dont tall the answer ill think on it more........ 1 Link to comment Share on other sites More sharing options...
Saber Posted January 30, 2023 Author Share Posted January 30, 2023 (edited) Thinking in the first situation when it hadnt been simplified............The buckets with membranes i mean......... The buckets @ the bottom experience more pressure in the membranes right ? so the left membranes that protrude out less and the right ones that go inside are pushed more............... So the volumes at the bottom are less = the buoyant force is less. @ the bottom right ? And if we assume that the weigh force of each bucket is 10 for example and the buoyant forces of each bucket in order of size from 1 to 4 is like this then the over all downward force on each one is like this ........ IN that case on the right side as the buckets go down.........they have to accelerate......... and on the left side.....as they travel up they have to decelerate right ?? Edited January 30, 2023 by Saber Link to comment Share on other sites More sharing options...
Genady Posted January 30, 2023 Share Posted January 30, 2023 27 minutes ago, Saber said: So the volumes at the bottom are less If the membranes are flexible but not stretchable, it will not happen. 30 minutes ago, Saber said: they have to accelerate They would accelerate until they reach velocity when the water resistance balances the gravity and buoyancy forces. 1 Link to comment Share on other sites More sharing options...
Saber Posted January 30, 2023 Author Share Posted January 30, 2023 So im not on the right path of thinking ? Link to comment Share on other sites More sharing options...
Genady Posted January 30, 2023 Share Posted January 30, 2023 2 minutes ago, Saber said: So im not on the right path of thinking ? That was an unnecessary complication. 1 Link to comment Share on other sites More sharing options...
Saber Posted January 30, 2023 Author Share Posted January 30, 2023 23 hours ago, Genady said: Let's simplify even more. Let's assume that the top wheel is above the surface. Then the cups on top turn from left to right while out of water and it doesn't matter what exactly happens there as there is no buoyancy on either side there anyway. So back to the most simplified version ....is it that the pistons have to enter water ( a very denser material ) from air..........and the force needed to go in it from a very lower density to a very higher one ? Link to comment Share on other sites More sharing options...
Genady Posted January 30, 2023 Share Posted January 30, 2023 24 minutes ago, Saber said: So back to the most simplified version ....is it that the pistons have to enter water ( a very denser material ) from air..........and the force needed to go in it from a very lower density to a very higher one ? That density has an effect if a body hits the water on high speed, but if it enters slow enough then the only force it needs to overcome is the buoyancy. Link to comment Share on other sites More sharing options...
Saber Posted January 30, 2023 Author Share Posted January 30, 2023 Sooo i have to admit i gave up.... Link to comment Share on other sites More sharing options...
Lorentz Jr Posted January 30, 2023 Share Posted January 30, 2023 35 minutes ago, Saber said: is it that the pistons have to enter water ( a very denser material ) from air..........and the force needed to go in it from a very lower density to a very higher one ? Forget about everything except the weights. Imagine that the belt turns just enough for one weight to change direction on each side, plus there are more weights in between. What effect does each weight have on the belt? They have to push on it or add energy to it if it's going to keep moving. 1 Link to comment Share on other sites More sharing options...
Saber Posted January 30, 2023 Author Share Posted January 30, 2023 (edited) 17 minutes ago, Lorentz Jr said: Imagine that the belt turns just enough for one weight to change direction on each side, Does that mean weighs on both sides reach to the bottom/tom simultaneously ? or the opposite of this ? The weighs only can pull right they cant push Edited January 30, 2023 by Saber Link to comment Share on other sites More sharing options...
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