The Scranton tribune. [volume] (Scranton, Pa.) 1891-1910, 1899-09-05
A CURIOUS QUESTION.
What Ball Would Do if Dropped
Through the Earth.
Iiladelphia Enquirer

From the Philadelphia Enquirer
Some persons are forever asking
funny questions. Here is sample:
If a hole passed through the center
of the earth and a cannon ball were
dropped into the hole, what would be-
come of the ball?
The answer is that in about one
hour and twenty minutes after it ha
disappeared down the hole the ball
would come back to its starting point,
having passed in that time twice
through the earth. If left free to fol-
low it's own inclination it would at
once drop back into the hole and re-
peat the performance, and it would
continue thus to travel through the
hole from end to end forever.
This is supposing that there were no
air in the hole to check the speed =
the ball, and that it We're acted upon
solely by the force of gravity.
The movement of the ball would be
essentially that of a swinging pendu-
lum, the main difference being that It
would move in a straight instead of in
a curved path. A pendulum is swung
by the pull of gravity. During one
half of its swing it falls during the
half gravity acts to give motion; dur
ing the other half. to take its motion
from it. The force is the same in both
cases. Hence the rise is exactly equal
to the fall. A pendulum once set I'M o
motion would swing forever, were l.
not for the resistance which It encoun-
ters from the air and from the friction
of its support.
Nh.N 1N,11
posed. being pulled down by gravity;
would fall with a continually increas-
ing speed toward the earth's center.
But the force which acted to pull it
down would become continually less
and less, until at the earth's center 1t
became nil. A particle of matter at
the earth's center is pulled in all di-
rectionS witN the same force. and
therefore it is practically not pulled
at all.
The rall would reach the earth's CEN
ter WI a velocity of about five miles
a second 1t would shoot past the CEN
ter because of its momentum. and
| thereafter the course would be an up
ward one. To take out of a moving
| body its motion requires an eXpendi-
ture of force exactly equal in amount
to that which gave it it's motion. The
| ball would rise against the pull OF
| gravity until it reached a height equal
to that from which it fell. 1t would
| rise to the surface Of the earth on the
| farther side. Then II would fall ba III
| just as does the bob Of a pendulum
and repeat the movement in a reverse
| direction.
If a pendulum-or say, a ball sus,
| pended by a string-is struck dexter,
ously when just at the end of it's swina
in a direction perpendicular to that in
which II swings it will be set to swing
ing in two ways simultaneously, an
the ball will then pursue an elliptic,
path, or, If the blow is just sufficien
to make it swing in the new direction
| to the same extent as i'm the first, thu
| path will be a circle. This ellipse ol
circle will be described by the bob o
the pendulum in the same time as i
requires for making one complete os
| cillatiOn. Similarly this cannon bal
would make it's double passage through
the earth in the same time as it woui;
take i'm circlng round the earth, jus
clear of its surface as a satellite. r.
! escape falling to the earth il wOulJ
need to travel at the rate OF a lttl,
over five miles second, and the periO
Of it's revolution round the earth woul"
be one hour and twenty minutes very
nearly.