THE NORMAL FORCE
When you stand on the floor, does the floor exert a force on you? Yes! As you stand,
you exert a weight on the floor, compressing the molecules in the floor, and as a
consequence, they push outward from your feet. When an object is in contact with a
surface, the surface exerts a contact force on the object. The component of the
contact force that’s perpendicular to the surface is called the normal force on the
object. (In physics, the word normal means perpendicular.)
Normal Force Notation
The normal force is
denoted by FN, or simply
by N. (If you use the latter
notation, be careful not
to confuse it with N,
the abbreviation for
the newton.)To get more technical, the normal force is a very real force that arises from the
compression of molecular bonds. In layman’s terms, it is a spring force; it’s the
reason why objects don’t fall through tabletops and you don’t fall through the floor.
If the object isn’t flying into the air or sinking through the floor, then the net force on
that object is zero.
Be aware, however, that the normal force and the weight are not an action-reaction
pair; that’s actually between Earth’s gravitational pull on the object (the weight)
and the object’s gravitational pull on Earth.