Explanation:
Have you ever noticed your hair standing out on a dry day, or how a fuzzy fleece blanket can make sparks if you rub two sections of the blanket together in the dark? Both of these things are caused by electricity—which also runs as current through wires behind light switches and electrical outlets. But the form of electricity that causes hair to stand up, known as static electricity, is much weaker (though strong enough that a buildup of static electricity can cause a slightly painful shock if you touch the right surface).
Because it's weaker, static electricity doesn't work as well to power light bulbs or appliances, but you can make it do some surprising things around the house.
Background
Static electricity works on similar principles as a magnet. It can create a positive or negative charge that can either attract or repel other objects.
Have you ever rubbed a balloon or fuzzy fabric against your hair and watched what happens? The rubbing action moves some of the loose negative charges (from atoms' electrons) in your hair to the surface of the balloon or fabric. This makes your (now) positively charged hair attracted to the (now) more negatively charged surface of the balloon or fabric. And because each of your hairs has a slight positive charge, like similar sides of a magnet, they will want to move away from each other, fluffing out your hair even more!
Water, which is two hydrogen atoms and one oxygen atom, also is made up of charged particles, with the two hydrogen atoms having a positive charge. Because in water’s liquid form these atoms are free to move around any which way, it can easily be affected by a static electrical charge.
Materials
• Three small Styrofoam cups (alternatively, you can use two paper cups to hold the water and an inflated balloon to provide the static charge)
• Toothpick
• Water
• Someone with a head of clean, dry hair
Preparation
• Carefully push a toothpick half way through the bottom of one of the Styrofoam cups. Don’t remove the toothpick—leave it stuck in the cup to ensure a gentle trickle of water when you fill it up.
• Hold this cup directly over the second Styrofoam cup.
• Fill the top Styrofoam cup (with the toothpick in the bottom) with water, and make sure that it is leaking a steady but small stream of water into the cup below.
Procedure
• Observe how the water is flowing straight down from the top cup into the one below.
• Rub the third Styrofoam cup against the head of someone with clean dry hair for several seconds to get a static electrical charge (you can tell this happens when the hairs start to stand apart from each other).
• Hold this statically charged cup near the stream of water without letting it get wet.
• What happens to the stream of water?
• Now move the cup away from the water stream. What does the water do?
• Extra: Try the activity with other objects, such as a paper cup, a balloon you've rubbed against your hair or other items. What works to change the water's stream? What doesn't?
Read on for observations, results and more resources.
Observations and results
What happened to the flow of water when the statically charged cup came close to it? What happened when you took the statically charged cup away? Why do you think this happened?
When you rubbed the Styrofoam cup in the hair, negative charges (electrons) moved from the hairs to the surface of the cup, giving the cup a negative charge. The water falling out of the top cup is made out of positive and negative pieces that are all jumbled together. But as the negatively charged cup approaches the stream, the positively charged parts of the water molecules (the hydrogen atoms) are attracted to the negative charge and move the whole stream toward the cup.
Why doesn't the water get pulled all the way sideways to attach itself to the surface of the cup? Even though the static electric pull between the negative and positive forces is strong, the water is still heavy enough to be pulled down by gravity. So when you take the charged cup away from the stream, gravity takes back over entirely and pulls the water straight down.
