The spirit of the age. [volume] (Woodstock, Vt.) 1840-1844, 1841-10-22

To determine the momentum of any body in
motion, we have only TO measure the force OF
power expended, TO produce that motion. Now ii
is known that falling bodies (settng aside fractions
and the resistance of the atmosphere,) acquire a
velocity of 80 feet per second by the force of grav-
it!y through IS feet perpendicular space; whereas
it requires the force of gravity through GA feet, to
produce velocity double the former, viz: Ga feet
per second. Hence the force of lOOlbs. of matter
at velocity of 80 feet per second, is adequate 10
raise lOOlbs. l6 perpendicular feet; and lOOlbs at
velocity of Ga feet per second, is adequate to
raise lOOIbs Ga feet Hence the velocity of Ga has
momentum quadruple of that of 80; or double
velocity has quadrupe momentum, and treble
velocity, nine-iod momentum, &c, The law of
forces here developed, renders it certain. that in
all experiments on the forces of moving bodies, this
law will be coniormed TO, as indeed it is. All the
statements and propositions based on the erroneous
formula, must therefore be incorrect; and should
by no meals be tolerated in our elementary books,
from which so many receive their notions of phys
zeal laws
The next class of errors which notice is found
in some books under the head of " action aud re-
action are equal" and in DR. Arnot's Elements of
Physics, under the following erroneous proposition,
via;-"There is no motion or action in the uni
verse, without concomlant and opposite action
of equal amount" will not enlarge this COM
munlcalion, by quotations of the numerous absur-
dltlcs, growing out Of the above erroneous propo-
silions, but will introduce one as the very climax
of these ahsurdles, and wilhal so papable, that it
will be no sooner heard than rejected, if common
sense be allowed to decide. 1t is as follows;
"Whcn amy elastic body as a billiard ballyrrikcs
another body larger than itself, and rebounds, it
gives tn that other, not only all the motion, which
it originally itself possessed this being done at the
mouien, when it comes 10 rest, but an additional
quantity equal to that with which it recoiS-owing
10 the equal action in both directions of the rcpuI-
sion or spring which causes the rcco When the
difference of size between the bodies is very great,
the returning velocity Of the smaller is nearly us
great us its advancing motion was, and thus it gives
II momentum to the body struck, nearly double of
what it originally itself possessed. This phenomc-
non constitutes the paradoXica case Of IN effect
being greater than its cause, and has led persons,
imperlectly acquainted with the subject, to seek
from the principal, II perpeiuum mobile"
The above quotation is somewhat amusing, as it
shows how great minds, in veneralion for scholas-
tic dogmas, will embrace errors which the meresl
child in reason will reject The truth in the case
is just what common sense decides it TO be, viz
that the smaller body communicates no more or
less momentum or motion to the larger body than
it loses itself For it is not true, that action and
action are always equal, or that in every case of
motion, there is contrary correspondent motion OF
equal amount, as shall be shown. We will take
a frequently quoted example, that of the discharge
of cannon in which it is enormously said, that
the gun receives momentum equal to that COM
municated to the projccti!e.