Electric forces | Forces at a distance | Middle school physics | Khan Academy

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 are 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 charge is, the stronger the electric force. So, the greater the electric charge, the greater the electric force. Another factor is 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.