Tuesday, March 2, 2010
Physics: Build a motor
As you may remember, a while back the kids magnetized an iron nail by wrapping it in many loops of wire and attaching the ends of the wire to a battery. This week the kids expanded on this principle to build a motor. Once again they made a coil of wire and inserted it into a circuit by resting it on 2 metal struts attached to a battery. Then they placed a small round magnet on top of the battery. The electro- magnet (the loops of wire connected to the battery) and the regular magnet exerted magnetic pulls and pushes on each other so that the coil rocked back and forth.
To make it spin, we had to get creative...the kids put white out on the tops of the wire where the coil made contact with the metal struts. Doing this broke the circuit half the time. What did this do? When the circuit was closed, the coil became magnetic, which gave it an initial push away from the other magnet. As the coil made half a turn, the circuit turned off, and the momentum kept it spinning, bringing the coil full circle.
In a perfect world, the coil would continue spinning until the battery ran out, but alas, we don't live in a perfect world. Besides gravity and electromagnetic forces, the kids had to contend with the most challenging force of all....FRICTION. The need to reduce friction explains why this activity took an hour, and not 5 minutes, and why by the time they got home, the motor may have stopped working.