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The science which treats of the action of forces upon bodies
and the effect they produce is called Mechanics.
Newton’s Laws of Motion.
The three fundamental principles of the relation between
force and motion were first stated by Sir Isaac Newton, and are
therefore called Newton’s laws of motion.
NEWTON’S FIRST LAW.
All bodies continue in a state of rest or of uniform motion
in a straight line, unless acted upon by some external force that
compels change.
NEWTON’S SECOND LAW.
Every motion or change of motion is proportional to the
acting force, and the motion always takes place in the direction
of a straight line in which the force acts.
newton’s third law.
To every action there is always an equal and contrary re-
action.
Gravity.
The natural attraction of the earth on everything on its
surface which will cause any body left free to move to fall in the
direction of the center of the earth is called the force of
gravity.
Acceleration Due to Gravity.
If a body is left free to fall from a height, its velocity will
not be constant throughout the whole fall, but it will increase at
a uniform rate. It is this uniform increment in velocity which
is called acceleration of gravity. It is usually reckoned in feet
per second. A body falling free will at the end of one second
have acquired a velocity of 32% feet, or, practically, 32.2 feet
per second; but it has fallen through a space of 16.1 feet,
because it started from rest and the velocity was increasing at a
uniform rate until, at the end of the second, it was 32,2 feet per
second; therefore, the average velocity during the first. second
can only be 16.1 feet. At the end of two seconds the velocity
has increased to 64.4 feet per second and the space fallen
(276)
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