Answer to Question #90552 in Mechanics | Relativity for Murari

Question

Pls explain the ans to the question which i am gonna ask below in the simplest way actually this concept only fears me and i am completely afraid of physics
My question is
What is normal force is it a form of electromagnetic force
If yes then how
You can explain me by example of book resting on table
Bec i dont understand what is happeninh with the book
What forces are actually acting on
Mg or normal force or electromagnetic force

Answer 1

What is the normal force? In a general sense, according to its 'geometrical' name, normal force is simply a force perpendicular to some surface. In mechanics, however, this force is being introduced to make calculations simpler. The normal force in this case prevents objects from falling through the surface. Imagine a book on the table. The force of gravity is applied to the book's center of mass and tries to pull the book straight to the center of mass of the earth. But everyday life experience tells us that book (if it is not too heavy of course) does not break the table, the floor, the earth's crust and so on. It is the normal force $N$ or $F_N$ acting upward against the force of gravity $mg$ that protects the book from falling.

As you have probably guessed, since the book neither moves upward nor falls down being on the horizontal table, the force of gravity and the normal force are equal to each other:

$$mg=N.$$

Is normal force related to the force of friction? Imagine you are pushing your book along a horizontal surface. You know that heavier book is harder to push. It occurs because of force of friction $f$ or $F_f$. And the interesting fact is that the force of frictions equals a coefficient of friction $\mu$ times the normal force:

$$f=\mu\cdot N=\mu\cdot mg.$$

By applying this equation, you 'convert' the vertical normal force to the horizontal force of friction acting against you.

What about inclines? Now imagine your book is lying on an incline. The force of gravity no matter what is the angle of inclination acts straight to the center of the earth, i.e. vertically downward. But as you have learned, the normal force acts normally (perpendicularly) to the incline.

If the surface is smooth, i.e. there is no friction between the book and the incline, the book will slide downward. Why? Look at the figure above. Do you see the small orange arrow directed to the lower left-hand corner? That is the projection $N_x$ of the normal force on x-axis. This projection makes the book slide. If there is enough friction, the force of friction will appear (along the incline to the right) and the book may not move.

Is the normal force an electromagnetic force? People's brains have ability to put unnecessary facts aside. When we considered previous questions, we could ignore the nature of these forces. But the table is made of molecules. When the book acts on the table, the molecules of the table are pushed by the molecules of the book and they stretch and bend downward, but the intermolecular forces between table's molecules may be strong enough not to let these molecules lose their bonds.

When you lift your book up, the normal force disappears, i.e. the pressure on the table disappears, i.e. the molecules of the book no longer interact with the molecules of the table, and the intermolecular forces come to their original state. So yes, since molecules interact by means of electron bonds, we can say that the normal force is a kind of electromagnetic force.

But we do not think about all this at a time, thanks to our brains.