Why one substance does not pass through another substance？

[obiscr]

TL;DR Summary

The problem of nuclei passing through each other.

1. Books and desks have only one atomic core

There is a book and desk, suppose the book and desk are composed of atomic atomic core and extranuclear electrons.

Now, the book moves down along the y axis, while the desk stands still or moves up.

Now there is a problem: the position of the x-axis corresponding to the atomic core of the book is 1, and the position of the x-axis corresponding to the outer electron of the book is 3; the position of the x-axis atomic core corresponding to the desk is 2, and the x-axis corresponding to the desk outside the atomic core The position of the electron is 4. In this case, the book and the desk will pass through each other, and the book will not be stably placed on the desk.

The above is when there are few atomic core in books and desks.

2. Books and desks have multiple atomic core

Assuming that there are many atomic core in the book and desk, the possibility of collision between the atomic core in the book and desk is also greater. At this time, this situation will occur: a part of the atomic atomic core collides, and the force generated between the atomic atomic core overcomes the universal gravitation, which makes the book unable to move down along the y axis. The phenomenon is that the book is inlaid on the table. Of course, the depth of the inlays may not be the same, and at the same time they are unlikely to pass through each other.

But what we encounter in the real world is that the book can be stably placed on the table. There will never be a situation where a book is embedded in a table.

I have always been curious about why this is, and I don’t know if anyone can answer this question. Is there a problem with my way of understanding this question?

Thank you！

 

[Baluncore]

Welcome to PF.
That is a good question.

There are many atomic cores, but they are very small and on the inside. The atomic cores never meet. The outer electrons of one object first meet and repel the outer electrons of the other. That is the normal situation for books on desks in Earth's gravity.

Solid materials are elastic. When you place a book on a desk, they both deform slightly due to the forces on the objects. A book does sink into a desk. https://en.wikipedia.org/wiki/Young's_modulus

A solid material is a network of strong chemical bonds that connect the atoms and maintain the shape of the solid material. Books and desks are usually made from cellulose which is a polymer chain, strong enough to keep trees standing.

As two solid materials are increasingly forced together, if the bonds do not all break so the structure collapses, then the objects may become welded together.

In order for one solid bonded object to fall through another it is necessary to first break half of the chemical bonds. That will take a huge amount of energy. As one object passes through the other they will form a chemical compound, an alloy or a flowing liquid. What remains will be the original material, but will not be in the shape of the original objects.

 

[snorkack]

The phenomenon is that the book is inlaid on the table. Of course, the depth of the inlays may not be the same, and at the same time they are unlikely to pass through each other.

But what we encounter in the real world is that the book can be stably placed on the table. There will never be a situation where a book is embedded in a table.

Suppose that there is wet paint or glue on the table. Then as you press the book on the table, molecules of the paint pass into the book. As the paint, lacquer or glue dries, would you call the book embedded in the table/paint layer which is part of the table?

 

[obiscr]

Suppose that there is wet paint or glue on the table. Then as you press the book on the table, molecules of the paint pass into the book. As the paint, lacquer or glue dries, would you call the book embedded in the table/paint layer which is part of the table?

Yes, I think it might be like this on a microscopic level.

 

[snorkack]

Yes, I think it might be like this on a microscopic level.

The thing here is that you can pass a liquid through a sieve, cloth, paper etc. and have the liquid reconstitute on the other side because the atoms in the individual sieve threads, cloth or paper fibres are more strongly bonded to other atoms in the fibre and less strongly to the atoms of the fluid between the threads.
In order to pass through microscopic solid, like activated carbon or silica gel, the solid needs bonds that are stronger than bonds to the percolating fluid.

 

[obiscr]

The thing here is that you can pass a liquid through a sieve, cloth, paper etc. and have the liquid reconstitute on the other side because the atoms in the individual sieve threads, cloth or paper fibres are more strongly bonded to other atoms in the fibre and less strongly to the atoms of the fluid between the threads.
In order to pass through microscopic solid, like activated carbon or silica gel, the solid needs bonds that are stronger than bonds to the percolating fluid.

Got it. Thanks!