To understand electric fields and electromagnetic waves,
you need to know
how charges (such as "negative" electrons and
"positive" protons )
cause each other to move.
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Click the mouse anywhere in the box.
You created an electron!
It's a particle with negative charge and not much mass.
Yeah, but it just got sucked into the positive charge and swallowed.
That's because the positive charge exerts an invisible, attractive
force on the electron -- an electric force. Try putting the electron
in different places. How long can you
keep it alive?
If I put one near the edge of the box, it gets sucked in a lot
slower.
Yes -- the electric force is like an invisible spring,
but as the charges move farther apart, a weaker spring pulls them
together.
Now see what happens when you give the electron a little
"throw" as you set it down.
To do this, click-drag the mouse in any direction.
The line shows the direction of the throw and its length
shows the speed.
Hey, if I start it off just right, the electron keeps looping
around the proton and never crashes into
it.
Does this mean that the electric force is somehow different
when the electron starts with a
velocity?
No, the force, or pull, depends only on where you put it, not
on the velocity.
But an electron's motion depends on both the force on the
electron and its velocity, which are often in different directions.
See what happens when you first click on the button
"show force," and then put an electron down
with a velocity in a different direction.
To understand electric fields and electromagnetic waves,
you need to know
how charges (such as "negative" electrons
and
"positive" protons 
)
cause each other to move.
Click the mouse anywhere in the box.
You created an electron!
It's a particle with negative charge and not much mass.
Yeah, but it just got sucked into the positive charge and swallowed.
If I put one near the edge of the box, it gets sucked in a lot
slower.
Yes -- the electric force is like an invisible spring,
but as the charges move farther apart, a weaker spring pulls them
together.
Hey, if I start it off just right, the electron keeps looping
around the proton and never crashes into
it.
You've just created an early model of an 
Does this mean that the electric force is somehow different
when the electron starts with a
velocity?
No, the force, or pull, depends only on where you put it, not
on the velocity.
But an electron's motion depends on both the force on the
electron and its velocity, which are often in different directions.
See what happens when you first click on the button
"show force," and then put an electron down
with a velocity in a different direction.
