  The Doppler effect is a shift in the frequency of waves emitted from an
object moving relative to the observer. By observing and analysing the Doppler
shift in electromagnetic waves from astronomical objects, astronomers gain
greater insight into the structure and operation of our universe. In this
paper, a simple technique is described for teaching the basics of the Doppler
effect to undergraduate astrophysics students using acoustic waves. An
advantage of the technique is that it produces a visual representation of the
acoustic Doppler shift. The equipment comprises a 40 kHz acoustic transmitter
and a microphone. The sound is bounced off a computer fan and the signal
collected by a DrDAQ ADC and processed by a spectrum analyser. Widening of the
spectrum is observed as the fan power supply potential is increased from 4 to
12 V.
