Re: [Phys-l] Linear Air Drag

[Brian Whatcott <betwys1@sbcglobal.net>]

LaMontagne, Bob wrote:
> Brian,
>
> I'm not sure what "generally" means in this case. 
The general case I had in mind is the hollow ball bearing versus dense 
solid metal ball bearing.
You will see that in these cases the drag is not simply proportional to 
radius.
Or have I got it wrong?
> ... The terminal velocity is directly proportional to r^2 for the series of steel balls. The data form an amazingly straight line of slope 2 on a log-log plot.
>   

For steel balls whose weight is a cubic function of radius, I'm pretty 
sure you're right. For balls with other weight functions of radius, I 
expect you're wrong.
But, I expect you would say the same?
> /snip/
> I don't think it's generally true however, that large balls drop faster 
> in viscous liquids,  though denser or heavier balls would, wouldn't they?
>
> Brian W
>
> LaMontagne, Bob wrote:
>   
> > /snip/ The relevant drag formula in this case is Resistance = C r v, where C is a constant and r is the radius of the sphere. The terminal speed becomes proportional to r^2. /snip/
> > Bob at PC
> >