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98 Making Things Move

Electrical Power
You will likely need to use electricity at some point in your project, unless your
creation is powered directly by wind or a human (or a hamster). Just as a ball on top
of a hill will roll from a higher potential energy position to a lower one, electricity
flows from a high potential source to a lower one. The high potential is called the
power source (or just power). The low potential is called the ground, which doesn’t
necessarily mean the ground you’re standing on, but it can—that’s where the term
comes from.

Lightning starts out as a powerful charge just looking for a place of lower energy to
discharge, so it finds the fastest path to the ground. When you walk across a carpet in
your socks and pick up positive charge, you get a shock when you touch a doorknob
for the same reason—your high charge is looking for a lower energy place to go. Your
charge jumps to the doorknob and creates a spark, just like a tiny lightning bolt.
Metals are good conductors of electricity, so electric charge flows through them easily.
Since the doorknob is metal, possibly attached to a metal door that is hung on a
metal frame, it provides a great place for your charged-up energy to travel. Your sister
is also a great place to discharge built-up static electricity. Since humans are about
60% water, and water is very conductive, your high charge will escape using her body
as the ground. (Note that sisters do not always appreciate the shocking result of this
grounding experiment.)

For the projects in this book, the ground will not usually be the earth (or your sister),
but a strip of metal that is isolated from the power source so it stays at a lower
potential energy level. Sometimes the ground is just the negative terminal of a battery.

The relative difference between any high-energy and low-energy point is called the
voltage and is measured in volts (V). If we compare electricity to the flow of water,
voltage is like water pressure that comes from a pump, and wires are like pipes. The
amount of voltage, or water pressure, gives an idea of how much work a power
source can do. For batteries, you can read this voltage “pressure” on its label. Find a
standard AA battery and you’ll see 1.5V marked somewhere on it.

As an experiment, take an AA battery and your multimeter (like the SparkFun item
TOL-08657). Make sure the black probe is in the hole marked COM and the red probe
in the hole marked HzVΩ. Turn the dial to V and hit the yellow button to turn it on.