The Washington times., 1922-04-21
Eminent Astronomer and Author
ity on Subjects OF Scientific
Interest,

How does the gravitation Of
the earth compare with the
gravitation OF the planet Jupi-
ter? II the gravitation OF the
earth Is causing it's interior to
be molten hot would not the
gravitation OF Jupiter cause II
to be- molten hot to its very sur
face?-A. +. B., Chicago"
"HE total force OF gravitation
possessed by planet de-
pends upon the mass or
amount of matter contained in the
planet. Since Jupiter has a num-
Der of satellites revolving around
It we know with considerable aC-
Curacy the relative gravitativc
force Of Jupiter as compared with
that Of the earth. II we call the
earth's mass or force OF gravita'
ton !, then that OF Jupiter is
about 3l5 different calculators
vary n little).
This means that the attraction
Of Jupiter upon any body outside
its surface would be 315 times as
great as the attraction Of the earth
upon the same body, provided that
the distance OF the attracted body
from the center of Jupiter was tho
same as from the center Of the
earth.
1t means, too, that II our moon
were revolving around Jupiter in
stead of around the earth lat the
same mean distanCe), it's month
would be shortened to less than a
day and q half. Yet, singular as
1t may appear, the force OF Jup-
tiers surface gravity, 1. e., the
weight OF bodies lying on its sur
face gravity of the earth in the
same proportion that Jupiter's
total force OF attraction exceeds
the earths. This is due to the
slighter mean density and great
relative size OF Jupiter. It's volume
exceeds the earth's about as 1 800
to l, but its density is less than a
quarter as great as the earth's, so
that, as we have stated above, its
mass (or weight is only 315 times
the earth's. 1t weighs only a
quarter more than a globe OF
water Of its size would weigh.
The rule for finding the surface
gravity of any planet as compared
with the earth's is to multiply the
planets density by its diameter,
expressed in terms of the eErth's
density and diameter. Thus, Jupi-
ter's diameter ia about eleven times
the earth's diameter, it's density Is
0.24 Of the earth's density, and
eleven multiplied by 0.24 equals
2.64, which is the relative force OF
gravity on Jupiter as compared
with the earth.
There Is another way OF making
this calculation which may enable
you better to see the reason why
Jupiter, though having 315 times
the total attractive force OF the
earth, Is able. TO give to bodies on
its surface only about two and
three-fifths times the weight that
the same bodies would have on tho
earth. For this purpose you must
remember that the force of gravi-
tation varies invefsely as the
square of the distance, and that
the point from which the distance
is measured Is the center of the
attracting planet.
Now, since Jupiter has eleven
times the diameter OF the earth,
bodies on it's surface are eleven
times as far from it's center as sim.
liar hodies are from the center Of
the earth; therefore. the attraction
upon them Is the square Of eleven,
or 121, times less than It would he
II the distance from the center
werc no greater than Il is on tho
earth.
At the same time, Jupiter's total
attraction is ais times the earth's.
so that. 10 find out what the efCec-
tive attraction at Jupiter's surface
is, we must divide S15 by 121. and
the quotient, 26. representing the
relative force OF Jupitcr's surface
attraction. r. practically the same
as the result before obtained. and
would be precisely the same II we