Before we talk about friction, we must talk a little more about forces. A force is just a
vector, and the term Net Force, often seen as FNET, just means the sum of all of the forces.
Something that comes along with forces is a force diagram. A force diagram is a drawing that
shows an object, and the direction and magnitude of the forces acting upon it.
In the diagram above, you will notice a few things. The first is that there are some new
variables. In general "F" is the variable for force, but the letter in subscript after it tells
what type of force. Below is a chart of some, more will come as we need them.
| Symbol | Meaning |
|---|---|
| FNET | net force |
| FN | normal force |
| FG | force of gravity |
| FK | force of kinetic friction |
| FS | force of static friction |
Most of these forces should be self-explanatory, except maybe the normal force. The normal
force only occurs when an object is on a flat surface. The surface doesn't necessarily have to
be parallel with the ground, the object must be touching it. Here are some examples:
At this time we need to discuss balanced forces. When an object is not moving, the forces
acting upon it are said to be balanced. That means that they are equal. If forces are
unbalanced, the object moves in the direction that the greater force wants it to go.
Next lesson we get into the good stuff.
