Re: [Phys-l] ball floating in elevator

[Bernard Cleyet <bernardcleyet@redshift.com>]

A more "physical" apprehension is to picture the ball being heavier  
so it sinks in the water, however, this displaces water, but the  
water is equally heavier balancing the balls heaviness.  So no  
displaced water, i.e. no change.

bc

This experiment suggest that one should build a drop cylinder  
attached to the side of a building or in a stair well.  The columns  
outside the Exploratorium would be suitable.




On 2009, Apr 21, , at 09:42, Ken Caviness wrote:

> As Bob says, just think of the acceleration of the elevator as  
> adding to g, the "acceleration of gravity".
>
> Since water falls and air-filled balls in water rise under the  
> influence of gravity, they will do the same in the accelerating  
> elevator, although we should use (g+a) instead of g everywhere.   
> For a floating object we have equilibrium with Weight (downward) +  
> Buoyancy_Force (upward) == 0, so in magnitude, mg == rho g V, and  
> the actual value of g cancels out, so it makes no difference  
> whether the experiment is done on terra firma, or in an upward  
> accelerating elevator (replacing g by (g+a)), or on the moon, etc.