Question

Does stokes law (F= 6*pi*n*r*v, n= viscosity, r = radius, v = velocity) only apply to spheres, or does an alternative exist for other figures

Answer 1

nope.. only apply to spheres.. you should do something that i did.. i took a video of spheres falling in very highly viscous syrup, and using some motion tracker calculated the terminal speed and it turned out to be in good agreement with the theoretical calculated data :D..

are you interested?

Answer 2

and it has other limitations as well..only works for small radii spheres, and very lamilar flow cases..
otherwise it over estimates..
and for other figures you ll need to do a complicated derivation!..

Answer 3

The particular equation applies only to spheres for low-Reynolds-number motion.
Other shapes harder because orientations count, too. Could approximate cubes with inscribed and circumscribed spheres....

Answer 4

@douglaswinslowcooper.. can u tell me how do i calculate reynolds number for the motion!?

i know the formula.. R = density * velocity * a / viscosity

but i dunno what a is

for my example in which a sphere is falling down in a very highly viscous medium ?

Answer 5

a =length. Some sources claim that it's the radius of the sphere, and some say that it is the diameter

Answer 6

yea what exactly is that? :P

Answer 7

The length from the center to side = radius. The length from one side passing the center to the other side = diameter

Answer 8

i mean.. when a sphere is falling through a viscous medium .. like rainfall.. what do you consider a as ?

Answer 9

the raindrops radius = a

So for a raindrop R = (density of air * velocity of the raindrop * radius of the raindrop) / viscosity of air

Answer 10

oh for the sphere going through water a would be = spheres radius