AXIOMS, OR LAWS OF MOTION. Every body perseveres in its state of
rest, or of uniform motion in a right line, unless it is
compelled to change that state by forces impressed thereon.
PROJECTILES persevere in their motions, so far as they are not
retarded by the resistance of the air, or impelled downwards by
the force of gravity. A top, whose parts by their cohesion are
perpetually drawn aside from rectilinear motions, does not cease
its rotation, otherwise than as it is retarded by the air. The
greater bodies of the planets and comets, meeting with less
resistance in more free spaces, preserve their motions both
progressive and circular for a much longer time. The alteration
of motion is ever proportional to the motive force impressed;
and is made in the direction of the right line in which that
force is impressed. If any force generates a motion, a double
force will generate double the motion, a triple force triple the
motion, whether that force be impressed altogether and at once,
or gradually and successiv