Admittedly,
a discussion of energy is more likely to be useful to science-fantasy
GMs than to sword-and-sorcery folks. I know I’ve heard the term “an
unknown type of energy” pass a sci-fi GM’s lips more often than it
ought to. But even fantasy GMs might benefit from an overview of “mundane”
energy types, to give them some inspiration for “magical energy.”
Energy is often defined as “the
ability to do work.” Power is
how much energy is used per second. A “high-powered” device uses a
lot of energy in a small amount of time.
Example: A battery stores energy. If you use the batter in a device
that doesn’t require much power - say, a wristwatch - the battery
will last for a long time. Only a small amount of energy is taken
from the battery every second, so there is more energy for later.
If you put the same battery in an RC car, it won’t last as long. The
RC car needs more energy every second to power its motors than the
watch does, so it drains the energy out of the battery faster.
Most energy on Earth comes, directly or indirectly, from the sun.
Aside from whatever minerals and chemicals went into forming the planet
initially, our energy renewal source is the sun. Oil is just dead
plants that used sunlight to grow. Your dinner probably ate plants
or is plants. Without the sun, the planet would eventually die because
of entropy. Little bits of energy would be lost to waste heat until
no usable energy was left. The sun pumps new energy into our system
to keep it from running out of gas.
Real Energies
Kinetic energy is the energy of
motion. It depends on the mass of the moving object and the square
of the velocity of the object. This is why you should be more afraid
of a small, light, but very fast bullet than a heavier but slower
thrown rock. Hyrdoelectricity is created when the kinetic energy of
water is used to turn turbines.
Potential energy is stored energy.
A rock sitting on top of a cliff has stored potential energy. It depends
on the mass of the rock, the height of the cliff, and gravity. Potential
energy doesn’t do anything by itself, but it can be converted to another
sort of energy to do work. For instance, you could push the rock off
of the cliff, and then it would gather kinetic energy as it fell faster
and faster. The kinetic energy it has just before it hits the ground
is actually equal to its potential energy sitting on top of the cliff.
Heat energy
is just heat. It can make air rise, boil water, cause chemical
changes that bake your bread, and so on. Geothermal energy is the
heat energy of the earth brought to the surface.
Chemical energy is the result
of a chemical reaction of some kind. When some chemicals are mixed,
they give off heat. Fire is the result of releasing the stored chemical
energy of a plant. After using a high-powered battery device, pop
out the batteries and see if they are warm!
Electrical energy is hard to speak
about, since electricity is usually flowing from place to place. This
makes it more natural to speak about it in terms of power. Electrical
power is the product of voltage times current. If you compare electrical
flow to water flow, voltage is the height of a waterfall and current
is the amount of water flowing. High voltage can be quite safe! You
may have seen demonstrations where people are connected to thousands
of volts of electricity and are unharmed. The trick here is that the
current is very, very small. Think of standing under the Empire State
Building while someone drips drops of water on you. Not dangerous
at all! High current is what’s dangerous - imagine getting hit by
a firehose.
Nuclear energy is what you get
when you either split or fuse atoms into lower energy states. Every
atom has an energy - a “building cost” - associated with it. Sometimes,
you can break that atom into two smaller atoms which, together, cost
less than the original. This is fission, and the extra energy is what
makes the A-bomb and nuclear power plants work. On the other hand,
sometimes it’s cheaper to buy in bulk, and pushing two atoms together
to make a larger atom releases energy. That’s fusion, and it makes
the sun and the H-bomb work.
In-Game Energies
Magical energy:
Where does it come from? Does it have a nearly-infinite source,
like the sun? Or does the mage have to get energy from another source,
like an animal or plant sacrifice? From himself? (This might explain
the limits on spells per day).
Psionic energy: The brain already
has tiny electric current running through it. Maybe psionics is just
an extension of that. If this is the case, the psionicist is using
his own body’s energy to use his powers. He’ll be tired if he uses
them a lot, just as if he’d run across town.
Divine energy: Many GMs tie a
deity’s power to its number of worshippers. The act of worship might
create a sort of psionic energy the deity can collect. The deity can
then redistribute this energy in the form of miracles or spells to
faithful clerics.