2 explanations for normal force

[mishima]

I have heard 2 informal explanations for the normal force during a situation like a book resting on a table:

1. The springiness of the atomic lattice in the table attempts to restore its original structure, thus pushing the book.

2. Since there are electrons on the outside of both the book and the table, the book is prevented from falling through (- repels -). Some even say this is the Pauli exclusion principle, not just electrostatic forces. Those particles can't occupy space already occupied.

Which one is correct, or are they both correct?

Then, if 2 is correct, say you wanted to float the book above the table using electrostatic forces. Would you need to put a charge on both the book and the table? Or could you just put a charge on the table and let induction push the book up (since all the electrons rush to the top of the book)? Thanks.

 

[Drakkith]

The springiness of the table is irrelevant. Even if it were a perfectly rigid object you would still get a repelling force between the atoms in the table and the atoms in the book thanks to their negatively charged electron clouds.

If you wanted to float the book a noticeable amount of distance above the table using electrostatics your would need to charge both the book and the table.

 

[mishima]

Ok, thanks. I had learned 2 as you said, but had seen 1 in some texts.

 

[Drakkith]

Well, it's not WRONG, it just doesn't explain the repulsive force at all. It itself is a result of repulsive forces within the object. (And maybe attractive too)

 

[PJC01]

I cannot say whether one explanation is more correct than the other without further evidence and analysis. Both explanations have elements of truth and can help us understand the concept of normal force in different ways.

The first explanation, involving the springiness of the atomic lattice, is based on the concept of elasticity. When an object is placed on a surface, the surface deforms under the weight of the object. The atoms in the surface are compressed, and they exert a force on the object in an attempt to return to their original position. This force is known as the normal force.

The second explanation, involving electrostatic forces and the Pauli exclusion principle, is based on the idea that like charges repel each other. In this case, the electrons on the surface of the book and the table repel each other, creating a force that prevents the book from falling through the table.

Both of these explanations are valid and can help us understand the normal force in different scenarios. However, it is important to note that the normal force is a macroscopic concept and cannot be fully explained by looking at the behavior of individual atoms or electrons.

In terms of floating the book above the table using electrostatic forces, it is possible to do so by charging either the book or the table. If the table is charged, the electrons on the surface of the book will be repelled and the book will float above the table. However, if the book is charged, the electrons on the surface of the table will be attracted to the book, creating a normal force that will keep the book from falling through. In both cases, the normal force is still present and is essential in keeping the book from falling.