Re: [Phys-l] Fields and touch?

["John Clement" <clement@hal-pc.org>]

Touch is only defined in a macroscopic way, and really has no meaning
sub-microscopically.  So if you use a microscope you will see that the
surface of your hand comes in contact (no separation) with the surface of
the table.

But sub-microscopically the atoms are not solid and have no definite
surfaces.  One can make a mathematical definition of where the surface is
located, but that is subject to interpretation.  Actually when you touch
something, bonds form between the two surfaces so in a sense
sub-microscopically the two surfaces penetrate each other slightly.  So
sub-microscopically there is no gap.

Remember that outside an atom there is no static electrical field because
the forces due to the protons and electrons are balanced on any nearby
object.  But if you think about it classically there is only a repulsive
force if the "edges" of the atoms overlap each other.

The model that you use for physics depends on what you are looking at and
the scale.  So macroscopic things you can talk about touch and use classical
mechanics.  But sub-microscopically you use quantum mechanics and a many
classical concepts such as touch can no longer be applied.  So in the HS
classroom students have to learn the difference between contact and
non-contact forces, but still understand that all the same laws apply to all
forces.

John M. Clement
Houston, TX

> When my hand rests on the table, do I touch the table? ...Or do the
> electric
> fields between my hand and table leave a gap between the to objects? Maybe
> it comes down to how "touch" is defined?
>
> -Tony
>
> --
> Tony Wayne
> Albemarle High School
> Physics Teacher
> Science Department Chair
> twayne@k12albemarle.org
> http://www.mrwaynesclass.com
> -
> Those who can do.
> Those who understand, teach.
>
>
>
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