B Slow Motion Appearance of Flags: Fluid Dynamics or Perceptual Illusion?

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Flags appear to move in slow motion due to a combination of perceptual illusion and fluid dynamics, particularly the formation of Kármán vortex streets as wind interacts with the flagpole. This phenomenon creates alternating vortices that influence the flag's motion, making it seem graceful and slow despite potentially strong winds. The discussion highlights the challenge of understanding these concepts without overly technical jargon, emphasizing the need for intuitive connections to physics. Additionally, the motion of large airplanes is compared, as they also exhibit similar slow-motion appearances under varying wind conditions. Overall, the exploration seeks to bridge everyday observations with fundamental physics principles.
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Why do flags appear to move in slow motion when they flutter in the wind, even though the wind can be strong and variable? Is this perception purely psychological, or are there physical principles (such as fabric dynamics or fluid mechanics) that contribute to this seemingly slow, graceful motion?
 
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What have you done to analyze this problem and to research it?
 
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Huge airplanes also appear to move in slow motion.
 
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Chestermiller said:
What have you done to analyze this problem and to research it?
I’m trying to build up my understanding of physics concepts by asking questions that emerge from everyday observations. I tried looking up 'flag motion fluid dynamics', but most of what I found was overly technical. That’s why I thought this forum might help me connect intuition with actual physics.
 
metehansure said:
Why do flags appear to move in slow motion when they flutter in the wind, even though the wind can be strong and variable?
As the wind passes a flag pole, it deviates alternately to the left and right, forming a "Karman street". The flag lies between the air that moves down one side of the pole, and the air on the other. It therefore shows the position of the boundary between the alternating vortices, as they move downstream with the wind.
https://en.wikipedia.org/wiki/Kármán_vortex_street
 
Baluncore said:
As the wind passes a flag pole, it deviates alternately to the left and right, forming a "Karman street". The flag lies between the air that moves down one side of the pole, and the air on the other. It therefore shows the position of the boundary between the alternating vortices, as they move downstream with the wind.
https://en.wikipedia.org/wiki/Kármán_vortex_street
Thank you so much for your clear and detailed explanation.
 
metehansure said:
but most of what I found was overly technical.
Such is life / Physics. :smile:
 

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