Have the child notice – did anything happen? Now show them how the electrical current could pass from the battery into the motor, but you haven’t completed a circuit. Now show how you can take the other wire and connect it to the other end of the battery pack. This makes a circuit. Now your motor works!
Whenever the metal clip is touching the battery terminal, the motor spins. When it’s not touching, the circuit is broken and it stops spinning.
Optional: you could add a switch into your circuit: You can make your own switch with an index card, paperclip and two paper fasteners (brads.) When the paperclip is touching both fasteners, it completes the circuit. What happens to the light? If you move the paperclip so it’s not connecting the fasteners, the circuit is broken. What happens to the light?
A challenge with using the motor for this experiment is that it is hard to see the shaft of the motor spinning (though you can hear it.) You can place something on the shaft to make it more obvious. I have put a large bead on there, and you can watch the bead spin. Or I’ve used a cork. Use a pen to poke a hole in the cork, and then put it on there.
You could experiment with the cork. Push one hole into the end of the cork, perfectly centered, and the cork should spin smoothly. Now poke another hole into the side of the cork, about a third of the way from the top. Now the cork is very lopsided, and makes the motor spin unevenly.
This experiment is a great lead-in to a future project: making a scribble bot. That unbalanced cork is what will make your scribble bot travel around the paper. You can also make wiggle-bots by taking a container from the recycling bin, taping on a motor (this one we unbalanced with a wood dowel), a battery pack, and decorations.
Here is a collection of more ideas for what you can do with a small motor.
Small children require supervision with this experiment or other experiments with motors, for safety’s sake.
Note: if you’re buying new motors and battery packs… at the top of the post, there are affiliate links to the best option I’ve found on Amazon. But my preferred motors are these from Teacher Geek. The battery packs had metal tabs on the ends, and the wires from the motor have alligator clips, so it’s really easy to hook things together and have them stay together.