Mammoth Memory

Motors, armature and momentum experiment

A simple visual experiment can be built in the classroom to create a motor.

Take two large eyed needles and sellotape them to the ends of a battery. Also stick the battery down on a table:

Large eyed needles taped to a battery

Take some insulated wire, about a ruler length long and wrap it around a thick pen as many times as you can but leave enough wire to stick out over each end of the battery. (Wrap the wire around the coil each side a couple of times to hold the wire together.)

Coils of wire between the eyes of two needles

Now with a scalpel remove the top half of the insulation on both sides of the wire. Just long enough that the needle eye will contact the copper wire.

In profile this would be as:

Wire with half the insulation removed

Thread the two ends into each side of the two large eyes of the needles.

Coil of wire held above a battery by needles

Now tape a magnet to the top of the battery either north or south pole facing upwards.

Magnet taped to the battery with a coil of wire held above it by needles

Now if you start to spin the coil you will find it continues to spin. (The coil will only spin one way so if you start to spin it and nothing happens spin it the other way.) 

Why do we only cut half the wire?

Lets take one configuration of the coil and simplify it as below:

Movement predicted by Flemings left hand rule

If we used Flemings left hand rule the motion above would be that the bottom half of the coil moves away from us. 

Force on the coil becomes reversed

When the coil spins over the force on the wire would be towards us.

The coil would stop.

A way to prevent this is to stop the current (electricity won't pass through the insulation) and no forces will operate on the coil for one half. What gets the coil around is momentum.

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