Have you ever noticed that some types of clothes are more susceptible to static cling than others? For example, a wooly sweater can have a lot of static cling, but clothing made out of cotton doesn't cling nearly as much. How well do other materials around the house produce static electricity? In this science activity you'll explore this by making a simple, homemade electroscope (an instrument that detects electric charges) and testing it out. The results may shock you!
Static electricity is the buildup of electrical charge on an object. This charge can be suddenly discharged (such as when a lightning bolt flashes through the sky) or it can cause two objects to be attracted to one another. Socks fresh out of the dryer that cling together are a good example of this attraction in action. Specifically, static cling is an attraction between two objects with opposite electrical charges, one positive and one negative.
Static electricity can be created by rubbing one object against another object. This is because the rubbing releases negative charges, called electrons, which can build up on one object to produce a static charge. For example, when you shuffle your feet across a carpet, electrons can transfer onto you, building up a static charge on your skin. You can suddenly discharge the static charge as a shock when you touch a friend or some objects.
Whereas objects that have opposite charges are attracted to one another (such as clingy, freshly-dried socks), objects that have the same charge repel. This principle is used in making an electroscope, which is a scientific instrument that detects electrical charges.
- Styrofoam cup
- Sharp pencil or skewer
- Plastic drinking straw
- Aluminum pie pan
- Clay (optional)
- Aluminum foil
- Styrofoam plate (Alternatively, the Styrofoam lid from a takeout food container would work, too.)
- A nonmetal desk or table (For example, a wooden, plastic or glass desk or table would work.)
- At least one material to test (It should be no larger than the plate or can be folded to be small and able to lay flat. Some of the different materials you could test include polyester, nylon, cotton, wool, silk, aluminum, plastic wrap, copper, wood and tissue paper.)
- To make your homemade electroscope, first make two holes near the bottom of a Styrofoam cup (on opposite sides of the cup), such as by pushing a sharp pencil or skewer through the cup. (Always use caution and an adult's help when manipulating sharp objects.) Push a plastic straw through both holes.
- Next, use tape or four small clay balls to secure the cup's opening to the aluminum pan (flipping the cup upside down). If you are using clay, stick four little balls of clay (each about one half inch in diameter) to the rim of the cup, then turn the cup upside down and stick it to the aluminum pan. Adjust the straw's position so that one end of the straw is right above the edge of the pan.
- Cut a piece of thread with a length that's about two or three times the distance between the straw and the pan's edge. Tie a few knots in one end of the thread.
- Cut out a one-inch square of aluminum foil. Use it to make a ball around the knots in the thread. The ball should be about the size of a marble or smaller and be just tight enough so it does not fall off the thread.
- Tape the thread to the tip of the straw so that the ball of foil hangs straight down from the straw, just touching the edge of the pan. Why do you think it's important that the ball touches the pan? Adjust the straw's position if needed. (If the end of the thread without the ball is dangling down and touching the pan, cut it so it does not touch the pan.)
- Your homemade
electroscope is now ready for testing! When working with electricity, take precautions and beware of electric shock.
- To test your electroscope, create some static electricity by rubbing a blown-up balloon on a Styrofoam plate. Rub the Styrofoam plate several times with the balloon. How do you think this creates static electricity?
- Quickly place the electrically charged plate on a desk or table (that is not metal). Then place the electroscope you made on top of the plate. Be sure to only hold the electroscope by the Styrofoam cup and not by the aluminum pan, otherwise it will not work! Why do you think this is?
- You should see the aluminum foil ball move away from the edge of the pan. Why do you think the ball moves like this? Can you explain what is happening?
- Now, touch the ball with your finger. What happens?
- Now that you know your electroscope works, you can use it to test the static electricity present in other materials. To do this, first discharge your electroscope by touching the pan with your finger. Next, rub the material you want to test with the balloon several times to charge the material. Then quickly lift up the electroscope (holding it by its Styrofoam cup) and place the test material on top of the Styrofoam plate so that the material is laying flat on the plate. Make sure the material is not touching the table. Then place the electroscope on top of the object. What happens to the aluminum foil ball? Why do you think this is?
- Again, touch the ball with your finger. What happens this time?
- Based on your observations, was the material you tested able to hold a static electric charge?
- Extra: Use your homemade electroscope to test even more materials. Which ones can hold a static charge and which can't?
- Extra: You can also use your electroscope to investigate which materials conduct the most static electricity. This is because the farther the aluminum ball moves from the aluminum pan, the bigger the charge from the test material is. Which common household materials can build the greatest electrical charge; which ones the least?
- Extra: Some objects become negatively charged and other objects become positively charged with static electricity. Try to discover a way to investigate this. Does this kind of electroscope detect both types? How can you tell the difference between the two?
- Extra: Static electricity is not good when it gets in your clothes! Try an experiment rubbing an object with a dryer softener sheet (such as Bounce) after rubbing the object against a balloon. How do dryer sheets work? What happens to the electroscope reading after rubbing a charged object against a dryer sheet? How do different dryer sheet products compare?
Observations and results
Did the aluminum ball on the electroscope move away from the pan when you placed the electroscope on the charged Styrofoam plate? Did the other material you tested behave similarly or not move the ball at all?
When an object, such as the Styrofoam plate, becomes electrically charged, it can be either positive or negative. (If an object has a lot of electrons, it is negatively charged; if it does not have many electrons, it has a positive charge. Whether an object tends to gain or lose electrons depends on the type of material it's made of.) When a charged object (such as the charged Styrofoam plate) touches the aluminum pan of the electroscope, the charge (or electrons) easily moves through the metal pan. Because the aluminum ball touches the pan, the ball gains the same charge as the pan—they are both either positive or negative. Because objects that have the same charge are repelled by one another—the ball is pushed away from the pan. Materials that tend to gain or lose electrons include wool, human hair, dry skin, silk, nylon, tissue paper, plastic wrap and polyester—and when testing these materials you should have found that they moved the aluminum ball similarly to how the Styrofoam plate did.
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