~Forms of Energy.--~There are nine forms of energy that you can make use of in your experiments and in your inventions, and these are:
{ Bodies in Motion--kinetic. { Bodies under Stress { ENERGY OF MASSES { (like a coiled spring). { Potential. { Bodies attracted by { { Gravitation. { { Sound--both kinetic and potential.
{ Heat. ENERGY OF MOLECULES { Molecular and Atomic Energy. AND ATOMS { Chemical Action.
ENERGY OF ETHER { Electric and Magnetic Actions. { Light and Invisible Radiation.
~Machines and the Principles of Machinery.--~A _machine_ is a contrivance of mechanical parts by which energy is transferred from one part to another. Beside the amount of energy required for doing useful work there must be an extra amount for overcoming the friction. Remember that no machine can either create energy or increase it, and, as you have seen, every machine wastes some energy in friction; this being true it must be clear then that it is impossible to make a machine which when once set in motion would continue to run forever, or at least until its parts were worn out. So don’t waste _your energy_ in trying to invent a _perpetual motion_ machine.
~The Uses of Machines.--~These are many and varied from a commercial point of view in that they are designed to do better, faster or cheaper work and sometimes all of these good qualities are found in a single machine.
From a mechanical point of view, though, a machine is used to
(1) Change one form of energy into another form, as steam into electricity.
(2) To make a slow moving, but powerful force produce a high speed or velocity, as in a sewing machine.
(3) To change a small, fast moving force into a powerful force, as in the action of a crowbar.
(4) To change the direction of a force so that the power can be applied where and when it is needed, and
(5) To make use of whatever force is at hand as the strength of animals, wind, water, steam, gas and electricity.
~The Six Mechanical Powers.--~As a matter of fact there are really only two of these, namely the _lever_ and the _inclined plane_, the other four, that is the _wheel_ and _axle_, the _pulley_, the _wedge_ and the _screw_ being simply modified forms of the first two.
[Illustration: FIG. 37A. A LEVER OF THE FIRST CLASS]
