# Friction force (Fluid - Plane

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How can I calculate the friction force applied by a fluid ( air or water for example) on a plane moving in a straight line through this fluid ? Is there any formula to calc it?!?

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I'd suggest you take the projected area (of the object) onto a plane orthogonal to your velcity vector and multiply this by some crazy constant (maybe found in a school-physics book or on Google).

Hope you get what I mean ;-)

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I think that the formula is something like F = fluid density*plane area*plane speed ... but I'm not sure..heh....I wanna know the true formula and I'm sure it exists....please, if anyone knows it, tell me!! thanks....

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First hit on Google for "fluid friction" yielded this equation:

fdrag = -0.5CρAv2
C = numerical drag coeff, ρ = fluid density, A = area, v = velocity

from http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html

I imagine C will be nigh impossible to calculate, so you'll have take a guess at it. Given that a sphere has C = 0.5 and an extremely irregular surface has C = 2 (from the same site), an airplane would probably be--well, less than 0.5, but your guess is as good as mine :P

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it all depends on how much you know about the fluid.

probably nothing at all, so youd best stick with the simple approximation suggested by captainmikey.

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Yup. Search terms for the "correct" physics are "reynolds number" and "stokes law". These are "correct" for suitably relaxed definitions of "correct".

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Thank you a lot captainmikey! I have already seen this formula but I was not sure about.Now I'm sure this is the formula to calculate this kind of friction...About the C, it is the coefficient of friction and it only can be determined through physics test like 'wind tunels' tests.But, since it is for game programming purposes, It needn't to be too perfect.Its just make the programming and then test various values for C :P

Thanks for all...

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