[Phys-L] Re: Sizes of atoms

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

On Wednesday, July 06, 2005 8:54 PM, John Denker wrote:

> What I'm looking for is a hands-on, compelling demo
> that can be done in high school classes (no electron
> microscopes, no neutron scattering, etc.) and imparts
> a good "feel" for how big atoms are.  It's not an
> easy question;  there were a lot of very smart physicists
> who lived pre-1900, and they didn't figure it out.

How good of a "feel" do you want?

I know this doesn't give what you want (an estimate for N)
but how about rubbing a balloon with hair (or whatever) and
having it attract pieces of paper?  No perceptible mass
was transferred to/from the balloon yet whatever was
transferred exerted a force larger than the gravitational
force (on the paper).

This doesn't give you a number but to some students this has
more meaning than a number (e.g., Avogadro's or atom radius).

P.S. This also shows that there must be two types of charge
(repulsive and attractive).

____________________________________________________
Robert Cohen; 570-422-3428; www.esu.edu/~bbq
East Stroudsburg University; E. Stroudsburg, PA 18301
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