4.7. Types of Forces http://www.ck12.org
4.7 Types of Forces
- List and describe types of common forces.
The various types of common forces are discussed and analyzed.
Key Equations
Common Forces
Fg=mg Gravity
FN Normal force: acts perpendicular to surfaces
FT Force of tension in strings and wires
Fs p=−k∆x Force of spring stretched a distance∆xfrom equilibriumGuidance
Normal Force
Often, objects experience a force that pushes them into another object, but once the objects are in contact they do not
any move closer together. For instance, when you stand on the surface of the earth you are obviously not accelerating
toward its center. According to Newton’s Laws, there must be a force opposing the earth’s gravity acting on you, so
that the net force on you is zero. The same also applies for your gravity acting on the earth. We call such a force the
Normal Force. The normal force acts between any two surfaces in contact, balancing what ever force is pushing the
objects together. It is actually electromagnetic in nature (like other contact forces), and arises due to the repulsion of
atoms in the two objects. Here is an illustration of the Normal force on a block sitting on earth:
Tension
Another force that often opposes gravity is known astension. This force is provided by wires and strings when
they hold objects above the earth. Like the Normal Force, it is electromagnetic in nature and arises due to the
intermolecular bonds in the wire or string: