Investigating Stokes Law: Different Formulas, Different Results?

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The discussion centers on the differences between two formulas derived from Stokes' Law for calculating the settling velocity of particles. The first formula presented is Vt=gd^2(Pp-Pm)/18u, while the second is V=2/9*d^2*g*(Pp-Pm)/u. The user is confused about why these formulas yield different results despite both being related to the same physical principle. It is noted that the two formulas are essentially equivalent, with the difference arising from the constants used in their derivation. Understanding these constants and their context can clarify the apparent discrepancy.
LaurenG
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Hello all.

I'm investigating a little bit about stokes law in order to understand the settling velocity of falling particles and on the net i encountered with 2 different formulas and i simply can't find the reason why they are different. every formula gives me a different answer.
The 2 formulas are :
1. Vt=gd^2(Pp-Pm)/18u -
stokes_law_terminal_velocity.png

2. V=2/9*d^2*g*(Pp-Pm)/u -
3dbef61d20c1951c09a727ff8d4a809c.png


Any idea why they are different ?
Thanks.
 
Last edited:
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d=2R
 
davieddy said:
d=2R

Silly me, i knew it's something stupid.
Thanks :)
 

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