Activity/Demo overview:
The Van De Graaff machine creates a large amount of static electricity via friction with a conveyor belt on the inside. When a willing participant places their hand on the machine, the charges created by the machine distribute on their body and in their hair, making it stand up. This variation of the demo works best for a volunteer with hair that’s long enough to be somewhat weighed down. If there is no willing participant, another alternative demo with the Van De Graaff machine is to place a stack of pie tins on it and then turn it on. Because of the charges on the pie tins, they will repel and cascade off the machine. This demo covers concepts of static charges and how they interact with each other, so it’s a good demo to introduce the most basic concepts of electromagnetism. It can be more hands-on by allowing volunteers or allowing people to take turns placing their hand on it, or it can be show-only by having another presenter place their hand on the machine or using pie tins. Because this demo is all about static electricity, it works best when the weather is dry.
Activity/Demo Instructor Notes:
First, it’s best to have introduced the ideas that there are two charges, positive and negative, and how they behave with each other i.e. like charges repel, opposite charges attract.
If another human is placing their hand on the machine, especially an audience member, it’s best to remind them that the demo is completely safe, and they won’t get shocked if they listen to your instructions. Have the volunteer take off any rings or bracelets for safety, and then have them place their hand completely flat on the big metal sphere. Tell them to make sure they don’t take their hand off before you tell them to. Before turning on the machine, ask the audience what they think will happen when you turn on the machine. After they’ve announced their hypotheses, make sure that the grounding rod is on the big metal sphere and turn on the machine. If you don’t ground it when you go to turn it on, you might get shocked, and that can scare the audience. After it’s turned on and you’re a safe distance away, take the grounding rod off, and watch the volunteer’s hair stand up. The machine is pretty loud, so it’s best to let everyone “ooo and ahh” and then turn it off before further discussion of the physics. When you go to turn it off, make sure to place the grounding rod on the sphere again and then turn it off. After it’s gone quiet, you can tell the volunteer to take their hand off. Now, ask the audience what they saw and why that happened. Then, if necessary, you can explain that the charges were the same charge, so they wanted to get as far from each other as possible, so they went in the volunteer’s hair.
For the pie tin variation, balance the pie tins on the big metal sphere when the machine is off. Then, ask the audience what they think will happen when you turn the machine on. After they’ve given their hypotheses, place the grounding rod on the sphere before reaching to turn the machine on. When you’re ready, take the grounding rod off and watch the pie tins fly. After they’re done. Place the grounding rod on the sphere again and turn the machine off. Ask the audience what they saw and why it happened. Explain that the charges were repelling and went into the pie tins to get far apart, but when enough charges got into the pie tin, there was enough repulsive force to make it fly up in the air away from the others.