An object is moving if its position changes
against some background that stays the same. This stationary
background is called a reference frame. The change in position
in a reference frame is measured in terms of the distance
traveled by an object from a fixed point. The distance that
an object moves from this reference point per unit of time
is called speed. When the direction of motion is included
with speed, this is called the velocity of the object. Most
objects do not move at a constant velocity through the distance
that was traveled. Sometimes there are times of acceleration
and deceleration, in which the object is speeding up or
slowing down. Acceleration can be calculated by dividing
the change in velocity by the time.

A force is a push or a pull that can change an objects
velocity (and therefore its acceleration). The net force
is the combination of all of the forces acting on an object,
which determines whether the velocity of the object will
change. When the combination of forces acting on an object
combines to produce a net force of zero, the forces are
balanced. When the combination of forces acting on an
object combines to produce a net nonzero force, the forces
are unbalanced.

All objects tend to resist motion; this tendency is called
Inertia. An object in motion will remain at a constant
velocity unless an unbalanced force acts upon it; in the
same regards an object at rest, with zero velocity will
remain at zero unless a force causes it to move. Less
force is needed to redirect an object that has a low mass
than that of an object with a higher mass, which would
require a larger force. Therefore, the greater the mass
of an object the greater its inertia. Newton’s First
Law of Motion is, “An object moving at a constant
velocity keeps moving at that velocity unless a net force
acts on it. If an object is at rest, it stays at rest
unless a net force acts on it.”

Newton’s second law describes the relationship
between mass, force and acceleration. The unbalanced force
acting on an object equals the object’s mass times
its acceleration. We use Newton’s second law to
calculate an objects force due to gravity (weight). This
is found from the product of an objects mass and the objects
free-fall acceleration due to gravity.

For every action, there is an equal and opposite reaction.
Newton’s third law state that for every action force,
there is an equal and opposite reaction force. These forces
always act on different objects. Action/reaction forces
never cancel out. They cannot cancel each other out because
they act on different objects. The only time forces cancel
out (and add up to zero) is when they act on the same
object.