Newton's First Law of Motion
Newton's 1st law is also known as the Principle of Interia.
Its first known formulation dates back to Galileo, with a modification by Renee
Descartes before arriving with Isaac Newton. Its straightforward meaning is
that an object, free to move unencumbered by any kind of outside interference
(like gravity or friction), will continue on forever in its current state of
motion - even if that is being motionless. In this context, state of motion
means moving at a given speed in a specific straight line direction. (Descartes'
contribution to the principle of inertia is the idea of straight line motion,
by the way.) This concept of continuous, unchanged motion is referred to as
an object's inertia. The degree, or extent, of an object's inertia is
measured through the property called mass.
A number of scientists have viewed the first law as being included in Newton's
second law, discussed below, as a special case - that of motion with zero outside
force. However, it can be viewed as important in its own right because it defines
the observable property, unchanging motion due to inertia, that lets us relate
the individual perspectives where Newton's second law holds true.
You see, everyone has their own unique and personal view of how things happen
in the universe based on their own perspective and point of view - called a
reference frame in the appropriate mathematics. But, to be able to communicate
meaningfully with others, we all need to understand innately how to relate what
we see (observations in our reference frame) to what others see (their observations
in their reference frame). The principle of inertia permits us to establish
a concept of relativity: the mechanical workings of the universe are
the same in nature for me as they are for you. This Galilean postulate of
relativity is valid for any pair of individuals in inertial reference frames,
that is, reference frames where the principle of inertia is true. [Albert Einstein
proposed an extension to Galileo's postulate of relativity in that all physical
workings of the universe are the same in nature for everyone in inertial reference
frames. He extended from mechanical workings of material objects to those that
do not include ordinary material objects, like light. This became part of his
Special Theory of Relativity.] Since Newton's 1st law sets
the stage, so to speak, for the other two, it can be understood as necessary
on its own!
Continue to Newton's Second Law.
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