Re: [Phys-l] floating cork

[Bill Nettles <bnettles@uu.edu>]

Don't assume that the "net buoyant force" is vertical. The cork is not supported by the surface tension, but if the meniscus is there, one part of the cork is deeper than another, causing the buoyant force to be tilted. Another way to consider it is by looking at the normal forces acting on the cork at the cork/water interface. The "deeper" side of the cork will have a larger force so the net force is toward the low side of the meniscus, whether that is the center or the edge.

I hope I haven't gotten anything backwards here.

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of William Robertson
> Sent: Monday, April 18, 2011 5:42 PM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] floating cork
>
> Yes, "downhill" in the sense that the system is settling in at a lower
> potential energy, but I would like to know what's going on in terms of
> forces acting on the cork. I should also mention that if you "float" a
> paper clip instead of the cork (paper clip supported by surface
> tension rather than buoyant force), the paper clip does the opposite
> thing the cork does. There is no adhesion in the case of the paper
> clip, while there is in the case of the cork, which is what leads me
> to believe differences in surface tension are causing the movement of
> the cork.
>
> Bill
>
>
>
> On Apr 18, 2011, at 3:27 PM, Aburr@aol.com wrote:
>
> > In both cases the cork is just moving downhill
> >
> > Alex. F. Burr
> >
> >
> > In a message dated 4/18/2011 1:23:02 P.M. Mountain Daylight Time,
> > wrobert9@ix.netcom.com writes:
> >
> > Fill a glass half full of water and it will have a concave up
> > meniscus. ......
> >
> > . Now fill the same
> > glass to overflowing, so the surface  tension creates a concave down
> > meniscus.
> >
> >
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