TANGENTIAL MOTION REPRESENTS CENTRIFUGAL
PULL.--A tangential motion, or a horizontal
movement, seeks to move matter away from the
center of the earth, and any force which imparts
a horizontal motion to an object exerts a centrifugal
pull for that reason.

In Fig. 1, let A represent the surface of the
earth, B the starting point of the flight of an object,
and C the line of flight. That represents a
tangential line. For the purpose of explaining
the phenomena of tangential flight, we will assume
that the missile was projected with a sufficient
force to reach the vertical point D, which
is 4000 miles from the starting point B.

In such a case it would now be over 5500 miles
from the center of the earth, and the centrifugal
pull would be decreased to such an extent that the
ball would go on and on until it came within the
sphere of influence from some other celestial
body.

EQUALIZING THE TWO MOTIONS.--But now let us
assume that the line of flight is like that shown
at E, in Fig. 2, where it travels along parallel
with the surface of the earth. In this case the
force of the ball equals the centripetal pull,--or,
to put it differently, the centrifugal equals the