Vernier Software & Technology
Innovative Uses

# Measuring Motor Speed

Brian Lamore, physics teacher at the Chinquapin School, Highlands, Texas, has his students build a “Beakman’s” Motor to study electromagnetic induction. This simple motor can be built in a single class period and the activity is always a favorite of his students. But nothing makes an activity more interesting than a little competition, so Brian challenges his students to build the motor that will spin the fastest.

Instructions can be found at http://www.simplemotor.com/bmotor.htm

Brain uses the Voltage Probe to indirectly measure the motor’s rotational speed. He connects the Voltage leads to the motor and measures the voltage of the circuit. As the motor turns, the induced EMF causes a drop in the overall voltage in the circuit. Brian collects data for 2 seconds with a sampling rate of 1000 samples/s. Below is a graph of typical data, which shows 16 negative spikes over a span of 1.9 s. Calculating the average period and taking the reciprocal gives an average frequency of 8.4 Hz.

This is Brian’s third innovative use submission. See also Hurricane Rita and Battery Life Comparison.