South Bend news-times. (South Bend, Ind.) 1913-1938, 1918-07-04

Inere seems 10 De a perpetual
fascination about the time honored
question of what would happen 10
a body let fall into a straight hole
bored through the center of the
earth. 1t is a good question. too
a useful kind Of scientific fairy tale
-because it presents the law of
gravitation in a form that appeals
70 the imagination. and thus awak-
ems a curiosity about scientific prin-
ciples which il might be hard TO
arouse in any other way.
/ Several letters recently received
show how widespread is interest
in primary science. one man thinks
/ that the body would stop on reach
| ing the center of the earth, be-
cause at that point gravity ceases
to pull it; another thinks it would
/ 90 on and reach the surface on the
| other side by virtue Of centrifugal
| force"
1t is also suggested that inside
the earth centrifugal and centri-
| petral forces neutraiize each other.
A man may find innumerable more
wasteful ways of passing his time
than in striving 70 crack nuts like
these for they are really full of
meat"
II should be understood that in
dealing. in an elementary way,
with problems of this kind certain
summary assumptions must be
made TO begin with in order TO get
( rid of complications that only
serve TO confuse the general re-
suit aimed at. For instance, it is
/ necessary TO assume that the
| earth is a perfect sphere, and that
il is homogeneous, for otherwise
the direction OF gravity would not
be everywhere constant nor TO
cussed exactly at the center. and
the resultant attraction upon the
falling body inside the tube would
not be always in the same abso-
lutte straight line.
Then, too, it would make a great
difference where the hole was
bored: i. e.. where its points OF
entry and exit we're placed. These
ought 10 be at the poles, and the
tubular hole should follow the
axis Of the earth, in order that the
BODY falling through IL might not
be deviated from d straight course
by the effects of the earth's rota-
ton.
Finally, it is necessary TO neg
lect the atmospheric resistance
since the opening would be hHed
with air OF varying density. which
would have a great effect upon
the motion Of the body. But, put
ting all these rehnements asic e.
some very interesting results, and
useful facts about that mysterious
force called graduation Cgravity
when the earth alone is concerned
as the attracting body, may be OBJ
tanned.
First. then, the force Of gravity
diminishes with the depth below
the surface. and becomes zero az
the center When the body has
fallen say 100 miles from the top
of the hole il is freed from the
attraction OF an upper shell Of the
earth 100 miles in thickness. and
when it reaches the center II is
freed from the WHOLE. attraction
. OF the earth. considered as a force
directed toward common central
point. because now al the parti-
4 cles COMPOSING the earth tend 10
draw the body in an outward d.
/ rection. and since these particles
are symmetrically placed all around
their ractions neUtralize each
other. or are balanced. and the body.
a. far a. the,- are concerned IL not
moved by any force
Nevertheless. having fallen 70
the center, or point Of no attraction
II viii not stop there. because the
/ Momentum that IL has gathered
I during its fall from the surface re-
mains and viii serve 20 drive il past
the neutral point. and Up the op-
pOsite side. with diminishing velo-
city. until IL reaches the other sur
/ face where IL viii come 10 rest for
am infinitely brief instant and then
Immediately fal back again. once