1st Law of Motion

Motion doesn't change
without an outside force..
Chapter 14 - Force & Motion
Newton's Laws of Motion
2nd Law of Motion

F = ma
This explains how much
a force will change the
motion of an ojbect.
3rd Law of Motion

For every action...
the force will effect the
motion of both of the
1st Law             Inertia
Newton's first law of motion states that

An object at rest tends to stay at rest and an object in motion
tends to stay in motion with the same speed and in the same
direction unless acted upon by an unbalanced force.

Objects tend to "keep on doing what they're doing." In fact, it is
the natural tendency of objects to resist changes in their state of
motion. This tendency to resist changes in their state of motion is
described as
Newton's conception of inertia stood in direct opposition to more
popular conceptions about motion.
The thought prior to Newton's day was that it was the natural
tendency of objects to come to rest
Moving objects, so it was believed, would eventually stop
moving; a force was necessary to keep an object moving. But if
left to itself, a moving object would eventually come to rest and
an object at rest would stay at rest; thus, the idea which
dominated people's thinking for nearly 2000 years prior to
Newton was that it was the natural tendency of all objects to
assume a rest position.
Galileo & Inertia
Galileo developed the concept of inertia. Galileo reasoned that
moving objects eventually stop because of a force called friction.
In experiments using a pair of inclined planes facing each other,
Galileo observed that a ball will roll down one plane and up the
opposite plane to approximately the same height. If smoother
planes were used, the ball would roll up the opposite plane even
closer to the original height. Galileo reasoned that any difference
between initial and final heights was due to the presence of
friction. Galileo postulated that if friction could be entirely
eliminated, then the ball would reach exactly the same height.

Galileo further observed that regardless of the angle at which
the planes were oriented, the final height was almost always
equal to the initial height. If the slope of the opposite incline was
reduced, then the ball would roll a further distance in order to
reach that original height.
Newton's first law of motion declares that a force is not  needed
to keep an object in motion. Slide a book across a table and
watch it slide to a rest position. The book in motion on the table
top does not come to a rest position because of the absence of
a force; rather it is the presence of a force - that force being the
force of friction - which brings the book to a rest position. In the
absence of a force of friction, the book would continue in motion
with the same speed and direction - forever!
(Or at least to the end of the table top.)
Video on Newton's 1st Law