The
normal force,
N, is the force exerted by a surface on a body which
is resting on it.
It is perpendicular to the surface and its point of application is at
the base of the block.
The visual simulates a block resting on a surface. The normal force is
the reaction to the force exerted by the surface area on the plane. You
can see how the variation of the traction force, which pulls away from
the surface, implies the modification of the value of the normal force.
If we decompose these forces on some axes we will
be able to study their effects more clearly.
If you click on and drag the red dot in the following visual, you will
be able to see what has been explained above in detail.