A View of Sir Isaac Newton's PhilosophyPemberton, Henry
Science
A View of Sir Isaac Newton's Philosophy
Pemberton, Henry
Newton, Isaac, 1642-1727. Principia
4. IF the body, instead of setting out in the line B C perpendicular
to A B, had set out in another line B G more inclined towards the
line A B, moving in the curve line B H; then as the body, if it were
to continue its motion in the line B G, would for some time approach
the center A; the centripetal force would cause it to make greater
advances toward that center. But if the body were to set out in the
line B I reclined the other way from the perpendicular B C, and were to
be drawn by the centripetal force into the curve line B K; the body,
notwithstanding any centripetal force, would for some time recede from
the center; since some part at least of the curve line B K lies between
the line B I and the perpendicular B C.
5. THUS far we have explained such effects, as attend every centripetal
force. But as these forces may be very different in regard to the
different degrees of strength, wherewith they act upon bodies in
different places; I shall now proceed to make mention in general of
some of the differences attending these centripetal motions.
6. TO reassume the consideration of the last mentioned case. Suppose a
centripetal power directed toward the point A (in fig. 74.) to act on
a body in B, which is moving in the direction of the straight line B
C, the line B C reclining off from A B. If from A the straight lines A
D, A E, A F are drawn at pleasure to the line C B; the line C B being
prolonged beyond B to G, it appears that A D is inclined to the line
G C more obliquely, than A B is inclined to it, A E is inclined more
obliquely than A D, and A F more than A E. To speak more correctly, the
angle under A D G is less than that under A B G, the angle under A E G
less than that under A D G, and the angle under A F G less than that
under A E G. Now suppose the body to move in the curve line B H I K.
Then it is here likewise evident, that the line B H I K being concave
towards A, and convex towards the line B C, it is more and more turned
off from the line B C; so that in the point H the line A H will be less
obliquely inclined to the curve line B H I K, than the same line A H
D is inclined to B C at the point D; at the point I the inclination
of the line A I to the curve line will be more different from the
inclination of the same line A I E to the line B C, at the point E;
and in the points K and F the difference of inclination will be still
greater; and in both the inclination at the curve will be less oblique,
than at the straight line B C. But the straight line A B is less
obliquely inclined to B G, than A D is inclined towards D G: therefore
although the line A H be less obliquely inclined towards the curve H B,
than the same line A H D is inclined towards D G; yet it is possible,
that the inclination at H may be more oblique, than the inclination at
B. The inclination at H may indeed be less oblique than the other, or
they may be both the same. This depends upon the degree of strength,
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