Newton's Law of Universal Gravity was and perhaps still is one of the greatest discoveries
in the science of physics. Sir Isaac Newton came up with this theory by comparing the
acceleration of the Moon with the acceleration of objects on the Earth. The law of universal
gravity depends on the amount of matter in the objects being attracted to each other, and
the distance between the objects being attracted to each other.
Isaac Newton formulated the general principles of motion into the Three Laws of Motion. According to the First Law of Motion, an object
at rest tends to stay at rest and an object in motion tends to stay in motion in the same
direction and with the same speed unless acted upon by an unbalanced force. There are two parts
to this law, one which predicts the behavior of stationary objects, and the other which
predicts the behavior of moving objects. The behavior of all objects can be described by saying
that objects tend to ‘keep on doing what they're doing', unless acted upon by an unbalanced
In the Second Law of Motion, Newton theorized that the acceleration or increase in speed of
an object is directly proportional to the magnitude of the force, the same direction as the
force, and inversely proportional to the mass of the object. Inversely proportional means if
one value goes up, the other value will go down, assuming everything else stays the same.
Forces result from interactions. The Third Law of Motion states that for every action, there
is an equal and opposite reaction. For every action force, there is an equal in size and opposite
in direction, a reaction force. Forces always come in pairs, known as "action-reaction force
pairs". Identifying and describing action-reaction force pairs is a simple matter of
determining the two interacting objects and making two statements describing ‘who is pushing
or pulling on who', and in what direction.