A force is an action applied to an object. As a consequence of the force,
the object may move, change shape or any other characteristic of the body.
Forces are classified accordingly with the following guides:
Forces


Contact Forces


Push (including kicks)

Pull

Noncontact Forces


Gravitational

Electric

Magnetic

Nuclear


Strong

Weak

Most of the forces study in these notes are contact
forces.
In the international system of measurement, the unit of force is the Newton
(N). The Newton is not a fundamental unit of measurement, it is derived from the meter, kilogram, and second. In fact,
The most important characteristic of forces is that they are vectors.
As such, forces have magnitude and direction, ; graphically,
forces are represented by arrows. The symbols to represent forces are the same
as those to represent any other vectors,
.
Algebraic operations between forces follow the rules for vector's operations.
In particular, the vector addition rules apply to forces. The following diagram illustrate the basic steps for obtaining the result
of applying different forces over an object.
Forces  Figure 1  Addition of Forces 



In particular, these figures explain the manifestation of the vector
characteristic of forces when apply to an object. The left most part of the
diagram represents the actual forces acting on the object including their
directions as well as their relative magnitudes. In the middle part of the
diagram, the two forces are considered as applied to the same point in the
object (see center of mass xxx) because, for simplicity, object are considered
punctual even when they are represented by dimensional draws. Until rotations are studied, all objects are in reality
considered points in space. The red diagonal vector, F, is the vector
addition of the two vectors that represent the two applied forces, F_{1}
and F_{2}. In the right most part of the diagram, the net effect of the
two applied forces is the force F pulling the object in the direction pointed
by the red arrow. Thus, the object does not move either horizontally or
vertically. The object moves diagonal in the direction represented by the
vector F. 

When several forces act on an object, the vector addition of these forces is
called the net force, .
If the vertical force is 4 N and
the horizontal force is 3 N; then the net force is


a)

7 N



b)

1 N


c)

25 N

N

d)

5 N


e)

None of the above.


