4 ms·

Just one more bit: "Air has viscosity". Without naming viscosity, the explication doesn't hold. If the air didn't have any viscosity, like it is natural to imag

by pif 11y ago

Just one more bit: "Air has viscosity". Without naming viscosity, the explication doesn't hold. If the air didn't have any viscosity, like it is natural to imagine, planes could not fly.

zby 11y ago
Not really - if a wing moves through fluid without viscosity it still has to move the particles down.
- onion2k 11y ago
  The impulse required to move particles of a fluid with zero viscosity would be zero, so the equal and opposite force that we call lift would also be zero. Consequently you couldn't fly if air had no viscosity.
  - dhimes 11y ago
    If the particles have mass then the impulse wouldn't be zero.
FiatLuxDave 11y ago
This is incorrect. A wing can impart momentum to air even in the absence of viscosity. However, the optimal wing shape is different. For an example of a wing that moves air "down" without viscosity, look at turbomolecular vacuum pumps: http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV_Pumps.pdf http://www.physics.rutgers.edu/ugrad/387/388s06/UHV_LEED/UHV...
meagain20000 11y ago
Is there such a thing as non-viscous fluid?
- mcguire 11y ago
  Yes, one example is superfluid helium. https://en.wikipedia.org/wiki/Superfluid_helium-4 https://en.wikipedia.org/wiki/Superfluid_helium-4 Viscosity is weird. https://en.wikipedia.org/wiki/Non-Newtonian_fluido https://en.wikipedia.org/wiki/Non-Newtonian_fluido