Re: atmosphere and normal force

[James Mclean <jmclean@CHEM.UCSD.EDU>]

> zachary_wolff@YAHOO.COM writes:
> Why doesn't this effect show up in scales where the load is supported
>  ON a spring instead of FROM a spring.  A standard bathroom scale
>  shouldn't function properly if the effect you're describing is really
>  happening.
I didn't realize it when I wrote my first message, but I think I answered
that in my second message.  The scale is 'tared' to read zero  with the air
pushing on it.  When you stand on it, *some* area A is covered, so the
scale doesn't see that force PA.  But the net atmospheric force on you is
also PA.  So although PA may be large compared to your wieght, the two
effects cancel out perfectly: PA-PA=0.

Robert Carlson wrote:
> One might attack this question as follows:
>
> 1.  Review Archimedes' Principle.
> 2.  Measure the weight of a mass in vacuum.
> 3.  Measure the weight of the same mass in air.
> 4.  Measure the weight of the same mass at various levels of submersion in
> water.
> 5.  Measure the weight of the same mass completely submerged in water.
Unfortunatly, this introduces the additional buoyancy force, which kind of
confuses the issue.

--
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry