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Several forces can combine to make a total, or net, force.

More than one force can act on an object at once. For example, two people could push on a book
at the same time. One person could push toward the ** left** and the other could push toward the

For example, if one person pushed the book with a force of ** 20 Newtons toward the left**, and the
other person pushed the book with a force of

As you can see, the net force is aimed toward the left. This object will move as if it had a single force of 2 Newtons pushing on it toward the left.

Forces can be positive or negative.

Actually, forces which are aimed to the ** right** are usually called

Basically, when you calculate the net force you ** add** up the separate
forces, as in:

**F _{1}** +

Two forces can cancel each other.

Now, perhaps the two people pushing on the book each push with the
** same strength**, again one person
pushing toward the left and the other pushing toward the right. In this case the two forces would exactly

When two or more forces ** cancel** each other out to create a

Forces in the same direction work together.

Also, consider the two people to be pushing the book both in the **
same direction**. If one person
pushed to the right with a force of 8 Newtons, and the other person also pushed to the right with a force of 6
Newtons, then the net force on the book would be 14 Newtons toward the right. In this case the two forces would

This object will move as if it had a single force of 14 Newtons pushing on it toward the right.

Forces can act in directions other than horizontal.

The above three situations have all been ** one dimensional**. When the only directions considered
are to the left or to the right, then the problem can be thought of as operating on a horizontal number line, usually
called the x-axis. Such situations occurring along one line are called one dimensional.

One dimensional problems may also be vertical. In our context here we might consider only forces that act up or down. That would be a one dimensional problem, also. It would be operating on a vertical number line, usually called the y-axis.

However, if several forces act upon one object they need not act only along one line. For example,
an object could be pushed toward the right by one force and upward by another. In this case the net force would
be neither simply horizontally toward the right nor simply vertically upward. It would be aimed in a slanted direction
upward and to the right. Nor would the size of this net force simply be the arithmetic sum of the sizes of the
two other forces. In this situation one would use ** vector mathematics** to calculate the net force.

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