Forces exerted on the ball

Forces exerted on the ball Three forces ate exerted on the ball  

When the ball falls at a constant velocity, the equiUbiium between these three forces is verified, in accordance with the fundamental law of dynamics. We can, therefore, write  

Not knowing Fp Wa,D,pf,v), equation [3.13] does not seem to take us much 

The problem is thus described by only two dimensionless numbers. We introduce the following two dimensionless numbers  

The use of the Reynolds and Archimedes numbers stands out as the most natural among a nnmber of possibilities. The fall velocity is the unknown of the problem, whose conditions are set by other parameters. Hence, the fall velocity is introduced only in the Reynolds number, while Archimedes number characterizes the properties of Ae ball and flnid (the conditions of the phenomenon). 

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The equihbrium between the forces exerted on the ball (equation [3.13]) leads to the dimensional form of Stokes law ... 

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