"Electricity and Tennis Balls"

• demonstrate the concept of DC electricity using their bodies and tennis balls

1. Select a student to play the battery and another to be the light bulb. Give the tennis balls (in a container) to the battery.
2. Explain that the idea is to give energy to the bulb from the battery so that it can light. This energy will have to be carried by something; in this case balls that represent electrons ('balls' of charge).
3. Have the battery gently toss the balls to the light bulb. The students should notice that this can only happen for a very short while before the battery runs out of balls. Ask how the bulb could be lit for longer. Possible answers include having more balls (ie. a bigger battery) or having the light return the balls quickly. The first answer would work, but again only for a very short while. The second answer introduces the idea of a circuit--a complete path where the balls are returned to their starting point ready to be given more energy and used again. (By the way, if you connect a bulb to one end of a battery only, will it light? The answer is no, but in fact a little current will flow for a very short time just as the balls moved to the bulb and stopped there in this demonstration, there is, however, not enough energy transfered to cause a glow!)
4. Now ask students how we could increase the power that the bulb is receiving, and hence light brighter. Obviously there are several possible answers.
   • One is to make the balls carry more energy by making them bigger--using basketballs or soccer balls, for instance. This would work but in practice we are generally limited to using electrons (tennis balls) which are small, negative charges. The bigger, positive charges don't tend to be the ones that move.
   • Another answer would be to throw the balls harder. This does have a direct electric counterpart--voltage (V). Voltage is simply a measure of how much energy each electron is given by the battery. If we send the same number of electrons, but give each one more energy (ie. a bigger 'push'), we obviously send more power.
   • A third answer is to send the balls over at a faster rate, that is, send more balls over each second. This corresponds to current (I), or amperage. The electric current is simply how many electrons pass by each second (though we actually count groups of electrons, since they are so small and there are so many of them!) Clearly, if we send twice as many identical electrons each second we are sending twice the energy.
   • Another thing we could do is both of the last two at once--send more balls, harder. This brings up a very simple equation-- The total power (P) is simply the product of the number of balls and how much energy each one has. In electrical talk we would say that power is the product of the current and the voltage. ie. P = I x V

If your students are having trouble with analyzing circuits have them act out the proposed circuit using balls as above. The only 'extra' idea needed is that electrons can only travel through wires, that is, you can only throw the balls to certain people. One way to implement this would be to use yarn to show where the wires are, then you can only throw the ball to someone to whom you are connected by yarn.

Also, it would be better to represent the batteries by two people each, one for each pole, one (the positive pole) can only catch the balls, the other can only throw.

Other components can also be added. For instance a switch might be represented by two people standing next to each other who can only pass the balls, not throw them, to each other and only when they are holding hands (closed) not when they are separated (open).