The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1915-08-25
NEWTON ON THE SUBWAY

From the Spokane Spokesman-Review.
I'm a subway train l got up to walk
to the rear entrance, as the train
= was slowing down for a stop, and it
was just like struggling up a steep, rocky
hill I nearly fell over backward. l sup
pose there is scientific explanation for
this, SO please tell me what it is"
Stranger in New York.
If some modern physicists are right
in their reasonings you were struggling
against the mutable demon called cleo
tricity in his most mysterious form. What
pushed you backward was the fundamen-
tai thing of the physical world-in-
ertia-and inertia ordinarily defined SIM
ply as resistance to motion. or to change
of motion. is according to the mathe-
matico- physical philosophers just referred
to, an electro magnetic phenomenon.
But putting aside all these specula-
tons, which sometimes smack too much
Of metaphysics, we can find perfectly
clear explanation by considering inertia
according to its plain, commonsense def
milton, as that quality of matter on ac-
count of which it requires force to change
it's condition of rest or motion.
If you stand erect in a subway train
when it suddenly starts you will be flung
backward, because your body, by virtue
of the property Of inertia (Which is a
kind of protest against interference. and
the very type of conservatism, refuses
to obey like slave the command of the
autocratic motorman to jump ahead. II
proposes to itself, on the contrary, to stay
as it is. But. being connected 10 the
floor of the train by its feet. its lower
portion is carried violently ahead, while
the upper portion, still protesting and re-
luctant and struggling to maintain its
position in space. finds it's support swept
away from beneath by the forward mo-
ton, and, accordingly, falls over back
ward.
In other words. the inertia OF the feet is
overcome more rapidly than that "a
body because they are more directly af-
fected by the movement Of the train.
Friction holds them fast to the floor. and
they have to start at once.
If, instead of being shaped like long
Cylinder, standing on end, your body
had the form of a cube, which is not
easily upset. its entire inertia would act
simultaneously to resist movement, and
you would slide backward on the floor
until the resistance had been overcome.
Now, take the case of which you speak.
In which your body, having acquired a
forward movement equal to that of the
train has changed its inertia of rest for
inertia of motion. The nature of the in
ertia is the same in both cases; it Is SIM
Fly pure conservatism or resistance to
change.
Having been compelled to set itself 60
ing. your body now clings obstinately to
the new state of things and resents any
effort either to stop its motion or to vary
its rate of moving. AS long as the train
is moving steadily at a fixed speed. you
can rise and comfortably walk forward or
backward, as you please. because your
movements inside the train are, indepen-
dent of the trains own motion. You are
sharing that motion of the train. just az
you would be sharing its state Pf rest ii
it were standing still. and in either case
your walking about the floor p unim-
peded.
But, when you rise from your seat at
the moment when the train Isl slowing
down for q stop, you encounter afain the
effects Of a change of state. resisted by