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[Phys-L] Re: Buoyancy question

If you are feeling evil, surreptitiously coat your forefinger with soap
before the doing the demo in a large shallow pan (cookie sheet). Reach
in and retrieve the needle with the soapy finger. Let the class try and
duplicate the demo...

Sooner or later someone will want you to float the needle again. A
teachable moment!

Scott



*******************************************
Scott Goelzer
Physics Teacher
Coe-Brown Northwood Academy
Northwood NH 03261
s.goelzer@comcast.net
*******************************************

On Dec 8, 2004, at 3:41 PM, John M Clement 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