Design Challenge Electric Motor Casey Wu Physics 4B Nov.-Dec., 2009

Materials wire plastic cup sandpaper 2 magnets 2 alligator clips battery

Building the motor Make a coil out of thick wire by wrapping it about 10 times around a tube of paper and leave a few inches of loose wire at opposite sides. Wind the wire around the coil to secure it. Use sandpaper to sand off all the insulation on one end and only one side of the other end.

Take a plastic cup and poke a hole about half an inch from the top. Poke another hole directly under the first hole, but about half an inch from the bottom. Create two similar holes on the opposite side. Poke a wire through each set of holes, in one hole and out the other. Sand off the insulation at the bottom end of both wires. Bend the top end of both wires to make a sideways S.

Rest the coil on the perch created by the twisted wires. Put magnets directly under the coil, one outside the cup and the other magnet inside the cup. The magnets’ fields are crucial to the success of the motor. This field, together with the magnetic field of the coil, either pull or repel, forcing the coil into movement.

The coil is spinning! Connect the sanded ends of the two wires to a battery using alligator clips. electricity is flowing through the circuit

Related Terms electricity magnetism current voltage circuit heat electrical energy mechanical energy (potential and kinetic)

Why this motor works Electrons flowing through a wire (in this case, the coil) creates a magnetic field. This magnetic field is repelled by that of the permanent magnets. So, with half the insulation sanded off one end of the coil, the coil alternates between a) having an electric current running through it and being pulled or repelled by the magnets and b) falling back down/continue moving because of inertia when no current passes through.

ENERGY An electric motor converts electrical energy into mechanical energy, which is in the form of either potential energy, kinetic energy, or both. Potential energy is energy that an object has because of its position. The stored energy has the potential to do work. Kinetic energy is the energy of motion.

CIRCUIT This electric motor is a circuit because current flows from the battery, through the alligator clips and the wires, into the coil to make it spin, out of the coil, through the wire on the other end, and back into the battery through other alligator clip. Electrons are able to flow through.

OBSERVATIONS Using Logger Pro, I learned that the motor makes 14 rotations per second while running on a 1.5V battery. Some of the electricity flowing through the circuit caused the coil to heat up. This heating of the motor is unavoidable. The motor can spin indefinitely without coming to a complete stop, but it tends to halt occasionally and start spinning again in the opposite direction.