# Quick question-book on a table

1. Jun 9, 2005

### briton

A book on a table.
the gravitational force of attraction of the bookon the earth is negligible...

if the reaction force is the electromagnetic force of repulsion of the book on the table, then why is the electromagnetic force of the table on the book negligible??

2. Jun 9, 2005

### Staff: Mentor

The action/reaction force pair is this: The earth exerts a gravitational force on the book, and the book exerts and equal (but opposite) gravitational force on the earth. (Of course, the effect of that force on the massive earth is negligible.)

Now you are talking about a different set of forces: The book pushes on the table (electromagnetic forces involved) and thus the table pushes on the book with an equal force. The force on the book is not negligible--after all, it's what's holding the book up!

3. Jun 9, 2005

### briton

sorry, I meant the electromagnetic force of the book on the table - this isn't negligible is it? It is of the same magnitude, but in an opposite direction to the force of the table on the book. mm I guess wht I really want to know, is what's happening on the ionic/molecular level... how is the table pushing with an electromagnetic/static force and how is the book pushing back?

4. Jun 10, 2005

### Chris Danger

Isn't it that the electrons of the book's molecules are close enough to the electrons of the table's molecules to provide sufficient repulsive force to keep the book afloat? (They're not really touching!)