B The Physics of blowing a puff of air

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When air is expelled from the mouth, it initially travels at maximum speed due to the confined space created by the lips. As the puff of air exits, it encounters stationary air, which creates resistance and gradually slows the air down. This process continues as the expelled air pushes against more stationary air, diminishing its velocity over distance. The discussion draws a parallel to rocket engines, where the immediate force is felt close to the source, but dissipates at a distance. Fluid mechanics can mathematically describe these phenomena, although it is complex and beyond basic calculus.
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If we noticed, when we released wind from our mouth with a constant velocity ,Why is the speed of the close part of our mouth is maximum speed and while gradually moving away is also gradually weakened until it is zero?
How it can be resolved using in mathematical expression?
 

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You mean why is a puff of air subject to air resistance?
 
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jhan said:
Why is the speed of the close part of our mouth is maximum speed and while gradually moving away is also gradually weakened until it is zero?
In the confined space of the small tunnel made by your lips, all of the air is moving rapidly. But when it exits your lips it runs into stationary air and pushes it out of the way. But then this air runs into even more stationary air and pushes it away. Which runs into even more stationary air...etc etc etc. On top of this, the air that's pushed out of the way is replaced by slow moving air coming in from behind, which itself then has to be pushed out of the way by your breath. The end result is that your breath only has a small distance in which it retains any significant velocity.

A similar thing happens with rocket engines. Standing directly underneath a large rocket engine would blow you away immediately (and cook you like a turkey under a blowtorch), but you can stand underneath a rocket flying high overhead and not feel even the slightest breeze.

jhan said:
How it can be resolved using in mathematical expression?
I throw in the towel when it comes to anything beyond basic calculus, of which fluid mechanics definitely is beyond.
 
Drakkith said:
I throw in the towel when it comes to anything beyond basic calculus, of which fluid mechanics definitely is beyond.
The physics of a towel thrown through the air as it gradually opens up must be quite complicated, I imagine.
 
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