- Have you ever taken
a shirt out of a dryer and found a sock stuck to it? If you have, you might have noticed that once you pull the sock off it was still attracted to the shirt even when they weren't touching. What is even happening here? Well, it turns out
there's an electric force between the shirt and the sock. Electric forces are a
type of non-contact force, which means they can act on objects that aren't even touching. If you've ever noticed two
balloons repelling each other, or if you've ever noticed your hair sticking to something like
a balloon or a sweater, that's what I'm talking about. But why is there an electric force between the shirt and the sock after
they're taken out of the dryer? Well, it turns out that
electric forces are caused by a property of matter
called electric charge. Matter is made up of tiny
particles that can have positive, negative, or neutral charge. Neutral just means that the
electric charge is zero, not positive or negative. When you add up all these
charges most objects tend to have a net charge
that is about neutral. Otherwise we'd be attracted
to all sorts of things, just like that sock. However, an object's charge can change. So in the dryer all that heat and movement allowed some negative
charges from the shirt to move to the sock. Now, when you try to separate the two, they're both electrically charged and there's an electric
force between them. So now that we know what
causes an electric force, let's look at what affects
its direction and strength. An electric force can
attract or repel an object. But how do you know if an electric force will be attractive or repulsive? Well, as the saying
goes, opposites attract. An object with a negative electric charge will be attracted to a
positively charged object. If the second object is
also negatively charged, well, the two objects will
experience a repulsive force and be repelled from each other. So in order to have the sock and the shirt attracted to each other they
must have opposite net charges because they're experiencing
an attractive electric force. What about the strength
of that electric force? Strength will depend
on a couple of factors. First, the charge of each object is proportional to the force. The stronger the charges, the
stronger the electric force. So the greater the electric charge, the greater the electric force. Another factor, how far apart the objects are from each other. The electric force will weaken
as the distance increases. So the force decreases as
our distance increases. As you move the sock away from the shirt eventually the attraction
between them is so weak that we don't even notice it. So the next time you find
yourself doing laundry and having to pull a sock off of a shirt, just remember invisible
electric forces are to blame.