Every year we have a student or two joining the practice as part of their requirements for vacation training. Without this training, engineering students cannot complete their degree course.

We usually ask the students to undertake a project, which then results in them writing a report. The reports are buried in one of the office hard drives and I thought that I might publish some of the projects for the general interest of Engineering News readers.

Okay, let us begin. First up: The Dog Bark Project. This was undertaken by student Tariro Andrew Goronga. I will quote from the project report: “This report gives a brief analysis of the spectrum of a dog’s bark. The analysis is done using Wavelab software and the particular dogs recorded barking are the office dogs, Tommy and Sophie. The barking was recorded at the Mackenzie Hoy office premises, in Pinelands, Cape Town, South Africa.”

In the report discussion it was noted: “This brief study concludes that a dog bark waveform is actually periodic and asymmetrical in nature, contrary to popular belief. It is also to be noted that, as easy as it may sound, it is very difficult to get an untrained dog to bark at one’s command.”

What Goronga found was that, in effect, a dog bark is not a series of impulses but has the characteristics of a periodic waveform.

Next project, written by student Bernd: “At the beginning of the twentieth century, acoustic means [were] used in mines to determine gas ratios in the air. In 1913, F Haber, a German professor, developed a whistle which should be able to show the methane content in air in ranges of roughly 0% to 5%.

“This methane whistle used the physical principle of beats to indicate the methane ratio to the miner. An increasing gas ratio should be determined by hearing an increased beat frequency.”

Bernd made a setup that consisted of two musical instruments (recorders). Each was fed from a chamber. In the one chamber was air and the other gas (carbon dioxide, not methane, the latter being considered too dangerous). Using pumps, the air was forced through one recorder and the gas through the other. The recorders produced notes which varied very slightly, resulting in a ‘beat’, or slow oscillation, which indicted the presence of gas in one recorder. Bernd concluded: “The experiments demonstrated the medium-dependent behaviour of sound. The formation of beats could be proven and clearly depicted. The suitability of the setup as an accurate gas analyser remains arguable. Spectators of the experiment found it hard to relate the beat to a gas ratio, that is to distinguish between a high, low or zero carbon dioxide content.”

More terrifying than the methane whistle was student Marcus’s experiments with a Rubens tube. A length of pipe is perforated along the top and sealed at one end – playing into the pipe at the other end is a small loud-speaker. Gas is fed into the pipe and the gas leaking from the perforations is lit. When the speaker is turned on, the standing wave will create points with oscillating (higher and lower) pressure and points with constant pressure (pressure nodes) along the tube.

The result is a whole line of flames which dance in time with the music. The student and the staff survived the experiments. I have videos of the experiment and they are truly scary. Forget “at home”. Just do not try this. Ever.

Finally, I have to include my two favourite projects. Students Mudi and Arne did the projects. One involved measuring the burning speed of different mixtures of gunpowder. We wanted to see if this could be accurately assessed by measuring the noise made by the gunpowder when it burned (uncompressed, so more slowly than in a gun) and noting the time the noise persisted (very accurate). The other project was to do the same experiment with smoke bombs. Did not work.

If anyone would like to try some of these projects yourself, he or she is welcome to do so. Just do not ask me how to make smoke bombs, gunpowder or flame tubes. Thanks.