Dead leaf falling...

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FALCON_12
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Dead leaf falling...




by FALCON_12 » 31/01/23, 14:59

sicetaitsimple wrote:-And yet they twirl, rising, falling depending on the moment.


if it was simple told me on another forum that a dead leaf that sometimes falls rises.

I said to myself that assuming at first that it is dimensionally stable, it was impossible for its center of gravity to rise whatever the moment of its fall.

In other words, I told myself that z(t), the height z of this center of gravity measured as a function of time, was necessarily a monotonically decreasing function. I think it is the same if it is deformable.

But I'm not sure.
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sicetaitsimple
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Re: Dead leaf falling...




by sicetaitsimple » 31/01/23, 15:21

You're nice but you can't read, because what I wrote is:

Cs you talk about "contact with reality", have you ever watched dead leaves twirl in the wind in autumn?
- Because they have a mass, admittedly not very important.
-They even have a weight, mg.
-And yet they twirl, rising, falling depending on the moment.
It's just that they are subject to aerodynamic forces acting on their surface opposing their weight, and causing their "apparent weight" to be sometimes negative, sometimes positive.


You understand "in the wind"?
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Re: Dead leaf falling...




by Obamot » 31/01/23, 16:02

- “I don't need anyone in a Harley Davidson"...
"What does it matter to me to die with my hair in the wind"...


: Cheesy:
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FALCON_12
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Re: Dead leaf falling...




by FALCON_12 » 31/01/23, 16:36

sicetaitsimple wrote:You're nice but you can't read, because what I wrote is:

Cs you talk about "contact with reality", have you ever watched dead leaves twirl in the wind in autumn?
- Because they have a mass, admittedly not very important.
-They even have a weight, mg.
-And yet they twirl, rising, falling depending on the moment.
It's just that they are subject to aerodynamic forces acting on their surface opposing their weight, and causing their "apparent weight" to be sometimes negative, sometimes positive.


You understand "in the wind"?


If I saw it Sicetait simple, but it made me think about this question. Why all this aggression?
Are you aware of his reasons? do you know each other?
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sicetaitsimple
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Re: Dead leaf falling...




by sicetaitsimple » 31/01/23, 17:15

FALCON_12 wrote:
sicetaitsimple wrote:If I saw it Sicetait simple, but it made me think about this question. Why all this aggression?
Are you aware of his reasons? do you know each other?


Thank you for your concern for my sanity, but when I see a new thread starting from a totally truncated excerpt from something I wrote, I take the liberty of correcting myself. There is no aggressiveness in that, just a correction vis-à-vis a writing (yours) that is totally funny... Then I have my way of expressing myself, you may not like it but it would just have been necessary in this case to avoid quoting me very partially so that it does not happen.
Come on, if there is no wind, I assure you the dead leaves fall without ever coming back up.
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Re: Dead leaf falling...




by Christophe » 31/01/23, 17:36

The mega tons of water permanently in the clouds on Earth also benefit from antigravity! : Mrgreen:
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FALCON_12
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Re: Dead leaf falling...




by FALCON_12 » 31/01/23, 17:43

sicetaitsimple wrote:
FALCON_12 wrote:
sicetaitsimple wrote:If I saw it Sicetait simple, but it made me think about this question. Why all this aggression?
Are you aware of his reasons? do you know each other?


Thank you for your concern for my sanity, but when I see a new thread starting from a totally truncated excerpt from something I wrote, I take the liberty of correcting myself. There is no aggressiveness in that, just a correction vis-à-vis a writing (yours) that is totally funny... Then I have my way of expressing myself, you may not like it but it would just have been necessary in this case to avoid quoting me very partially so that it does not happen.
Come on, if there is no wind, I assure you the dead leaves fall without ever coming back up.


But how to demonstrate it?
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Exnihiloest
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Re: Dead leaf falling...




by Exnihiloest » 31/01/23, 21:23

FALCON_12 wrote:
sicetaitsimple wrote:
FALCON_12 wrote:


Thank you for your concern for my sanity, but when I see a new thread starting from a totally truncated excerpt from something I wrote, I take the liberty of correcting myself. There is no aggressiveness in that, just a correction vis-à-vis a writing (yours) that is totally funny... Then I have my way of expressing myself, you may not like it but it would just have been necessary in this case to avoid quoting me very partially so that it does not happen.
Come on, if there is no wind, I assure you the dead leaves fall without ever coming back up.


But how to demonstrate it?

Indeed, they can go up, even without wind. If the sheet is in a vertical plane, it will pick up speed because the air resistance will be low. The slightest imbalance rotates the sheet in the horizontal plane, and it's like a glider that can gain altitude thanks to the kinetic energy it has acquired. But obviously each possible rise following a descent will be less than the previous one because it is always done by losing energy, and the sheet will eventually reach the ground.
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FALCON_12
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Re: Dead leaf falling...




by FALCON_12 » 01/02/23, 19:48

Exnihiloest wrote:
FALCON_12 wrote:
sicetaitsimple wrote:
Thank you for your concern for my sanity, but when I see a new thread starting from a totally truncated excerpt from something I wrote, I take the liberty of correcting myself. There is no aggressiveness in that, just a correction vis-à-vis a writing (yours) that is totally funny... Then I have my way of expressing myself, you may not like it but it would just have been necessary in this case to avoid quoting me very partially so that it does not happen.
Come on, if there is no wind, I assure you the dead leaves fall without ever coming back up.


But how to demonstrate it?

Indeed, they can go up, even without wind. If the sheet is in a vertical plane, it will pick up speed because the air resistance will be low. The slightest imbalance rotates the sheet in the horizontal plane, and it's like a glider that can gain altitude thanks to the kinetic energy it has acquired. But obviously each possible rise following a descent will be less than the previous one because it is always done by losing energy, and the sheet will eventually reach the ground.



So would you also say that z(t) is a monotonically decreasing function? (z(t): ordinate of the center of gravity of the sheet).
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