difference, The answer is, that it is in the
material itself. It was the mass or density which accounted
for the difference. It was mass multiplied
by speed which gave it the power, called, in
this case, momentum.

The iron ball weighing eight ounces, multiplied
by the assumed speed of 50 feet per second, equals
400 units of work. The cotton ball, weighing 1/2
ounce, with the same initial speed, represents 25
units of work. The term "unit of work" means
a measurement, or a factor which may be used to
measure force.

It will thus be seen that it was not the thrower
which gave the power, but the article itself. A
feather ball thrown under the same conditions,
would produce a half unit of work, and the iron
ball, therefore, produced 800 times more energy.

RESISTANCE.--Now, in the movement of any body
through space, it meets with an enemy at every
step, and that is air resistance. This is much
more effective against the cotton than the iron
ball: or, it might be expressed in another way:
The momentum, or the power, residing in the
metal ball, is so much greater than that within the
cotton ball that it travels farther, or strikes a
more effective blow on impact with the wall.