1
$\begingroup$

If we take an imaginary situation where a flag made up of any material is held straight, parallel to a flowing current of ideal fluid, and leave it as soon as the current crosses it?

Actually, when I saw a fan turn on in the direction of a flag and that the flag starts wobbling in a kind of oscillatory motion. I'm not getting the reason behind this behaviour.

$\endgroup$
  • $\begingroup$ A google search for "flag instability" reveals that this is an area of current research in fluid dynamics. It would be great to have a good technical answer to this question. $\endgroup$ – Nathaniel May 4 '17 at 15:34
1
$\begingroup$

A non flapping flag in a flowing air stream is in unstable equilibrium. Any small deviation from this position will be magnified and result in the oscillator flapping you observed. It is similar to a pencil balanced on its point.

| cite | improve this answer | |
$\endgroup$
  • $\begingroup$ And does this mean that in the previous situation, the flag will remain straight as long as no disturbance occurs? $\endgroup$ – Nabaneet Sharma May 4 '17 at 15:32
  • $\begingroup$ Yes, but that is mathematical abstraction that never hsppend. $\endgroup$ – Lewis Miller May 4 '17 at 15:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.