[Phys-L] Re: Buoyancy question

[betwys1 at SBCGLOBAL.NET (Brian Whatcott)]

If I place a sewing needle on a piece of tissue paper and
float it on clean water, the paper waterlogs and sinks,
and the needle floats.
If I examine the surface of the water I see that it is
depressed under the needle. The depression curves up
smoothly to the surface.
Though the water surface layer is supportive, I wonder if the total
depression displaces as much water weight as the needle weighs?

Brian W


At 02:41 PM 12/8/2004, you wrote:
> If you gently place an ordinary needle sideways on the surface of the
> water it will float.  I did this back in elementary school as I
> recall.  I think you have to lower it with a fork, and be extremely
> gentle.  The surface tension will hold it up.  But if you put a drop
> of detergent into the water, it sinks.  This is obviously not a
> buoyancy effect, as it will sink if you just drop it in or put it in
> point first.  It is a fun little amazing experiment.
>
> John M. Clement
> Houston, TX
>
>
> > I'm having trouble understanding Clement's response.
> >
> > On Tue, 07 Dec 2004 23:30:53 -0600 John Clement <clement@HAL-PC.ORG>
> > writes:
> > > I believe he is referring to the fact that a needle if gently placed
> > > on the surface floats.  This is a surface tension effect and not a
> > buoyancy
> > > effect. Of course if you add a drop of detergent it doesn't work.
> > >
> > > John M. Clement
> > > Houston, TX
> > >
> > > > Greetings everyone!
> > > >
> > > > I have a question pertaining to buoyancy phenomenon:
> > > >
> > > > What's the condition that a piece of iron released gently on the
> > > surface of water sink? Ignore surface tension.
> > > > Thanks,
> > > >
> > > > Hasan Fakhruddin
> > > > Instructor of Physics
> > > > The Indiana Academy for Science, Mathematics, and Humanities
> > > > BSU
> > > > Muncie, IN 47306
> > > > E-mail: hfakhrud@bsu.edu
> >
> >
> > Herb Gottlieb from New York City
> > A friendly  place to live and visit


Brian Whatcott    Altus OK    Eureka!