Timeline for Is there a height limit to the 'inflatable dancer'?
Current License: CC BY-SA 4.0
24 events
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Apr 29, 2023 at 21:36 | comment | added | jeremy_rutman | Adding 'QED' to the end of a statement doesn't make it correct, although you have demonstrated something - just not what you thought | |
Apr 21, 2023 at 13:28 | comment | added | jeremy_rutman | If L is length of tube and H is height it actually reaches then obviously H<=L , this has nothing to do with the outflow but the fact that the bottom end is tethered to the ground. Once again the question relates to conditions when H can or cannot reach L , you have tacitly agreed that the pressure drops with height. This drop of pressure will at some height cause the device to buckle and flail without ever fully inflating since the remaining energy in the stream does not suffice to lift up the weight of the tube above. | |
Apr 18, 2023 at 22:06 | comment | added | Kyle Kanos | At the end of the tube L is an outflow (which is the thing that makes it work as the wacky waving inflatable arm flailing tubemen), so H > L is surely never going to happen, ergo the height max is the length of the tube L. QED. | |
Apr 18, 2023 at 17:45 | comment | added | jeremy_rutman | Another way to look at it - can H=100km ? 1000km? And yet another way to look at it: remove as many variables as possible from the rhs of the 2nd equation in the question. | |
Apr 18, 2023 at 17:45 | comment | added | jeremy_rutman | There's the length of the tube L , and the height H it actually reaches. H=L only when the thing is inflated and erect. I agree at small H the pressure change is small. Perhaps you will agree that at large enough H the pressure change will be appreciable. If so then you will also (possibly) agree that for any given p_max there will be some height at which it will not remain rigid as the internal pressure will be too low. I have no idea how you reached the conclusion that 'I want' the max height to be both from and not from the airflow . | |
Apr 17, 2023 at 2:19 | comment | added | Kyle Kanos | My suggestion is not that it can reach arbitrary height, but that the maximum height of the inflatable is its physical height, which is independent of the pressure, density and velocity of air. You seem to want the max height to be from the source of the air flow (i.e. the fan) while also not from the source of the air flow. Note also that the pressure change in 5-6m that these things are in height is basically 0, so that surely wouldn't play a role (i.e., it's pretty much fully driven by the fan & the flapping from the vents releasing the air flow). | |
Apr 16, 2023 at 18:48 | comment | added | jeremy_rutman | I don't really understand what I'm supposed to pick between here? The original question, as it stands, seems pretty clear to me - what's the max height of this device in terms of p_max, g, and the properties of air. Your answer , that it can reach arbitrary height, seems pretty clearly wrong or at best an unsubstantiated guess. Consider the pressure as it changes with height, maybe that will make things clearer. | |
Apr 15, 2023 at 17:01 | review | Close votes | |||
Apr 16, 2023 at 21:39 | |||||
Apr 15, 2023 at 16:53 | comment | added | Kyle Kanos | The air pressure inside is caused by the size/power of the fan, which you've rejected as the intent of the question. Pick which one you want. | |
Apr 15, 2023 at 13:24 | comment | added | jeremy_rutman | It will stop 'standing up' when the air pressure inside is too small to inflate the tube and prevent the weight of the tube above from making it flop over. The air pressure will decrease with height. Ergo, there is likely a limit, depending on the interplay between gravity and the properties of air. | |
Apr 15, 2023 at 3:06 | comment | added | Kyle Kanos | The inflatable can go as high as its physical length allows, which is independent on any pressure, density, velocity or any properties of air you can think of. If it's 2m, it's 2m. If it's 5m, it's 5m. Simple as that. | |
Apr 13, 2023 at 23:41 | comment | added | jeremy_rutman | No not really since the size/power of the fan may be arbitrarily large. I am really asking 'how high can the inflatable possibly go' , in terms of p_max, g, and the properties of air. | |
Apr 12, 2023 at 22:15 | comment | added | Kyle Kanos | I see. So your question is more akin to, "For a given motor/fan, what is the largest inflatable that could be stood fully erect?" than "how high can the inflatable go?" that you've posted? | |
Apr 9, 2023 at 21:03 | comment | added | jeremy_rutman | The length of the inflatable is whatever you want, as long as it stays inflated - the question is how high can one of these go and actually 'work' given infinite supplies . What is the top height any part of such a device can reach | |
Apr 5, 2023 at 19:07 | comment | added | Kyle Kanos | Why is the height dependent on the flow parameters and not say the actual length of the inflatable? | |
Apr 5, 2023 at 19:00 | history | edited | jeremy_rutman | CC BY-SA 4.0 |
added result after assumption
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Jan 22, 2020 at 7:17 | comment | added | jeremy_rutman | assuming one is using flexible material that exists today, which has some max pressure p_max | |
Jan 20, 2020 at 1:47 | comment | added | Mike Dunlavey | What means "fully inflated"? Surely you could make it arbitrarily stiff by putting in more pressure. | |
Jan 17, 2020 at 0:00 | history | tweeted | twitter.com/StackPhysics/status/1217959913231724544 | ||
Jan 16, 2020 at 21:42 | history | edited | jeremy_rutman | CC BY-SA 4.0 |
added 61 characters in body
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S Jan 16, 2020 at 12:02 | history | suggested | DavidH | CC BY-SA 4.0 |
Edited MathJax
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Jan 16, 2020 at 9:53 | review | Suggested edits | |||
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Jan 16, 2020 at 6:55 | review | First posts | |||
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Jan 16, 2020 at 6:50 | history | asked | jeremy_rutman | CC BY-SA 4.0 |