Musical Fire Table Via Rubens’ Tube
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Now, it’s time for something bizarrely entertaining…and be sure not to try this at your home….
There are many ways in getting kids interested in studying math, physics, or chemistry. Check out how this Dane gets kids interested in physics and chemistry, in the video published on April 17, 2014, “Musical Fire Table!” below:
In this video, Rubens’ tubes are used. Check out what Rubens’ tube is, in excerpt from wikipedia, in italics, below:
A Rubens’ tube, also known as a standing wave flame tube, or simply flame tube, is an antique physics apparatus for demonstrating acoustic standing waves in a tube. Invented by German physicist Heinrich Rubens in 1905, it graphically shows the relationship between sound waves and sound pressure, as a primitive oscilloscope. Today, it is used only occasionally, typically as a demonstration in physics education.
A length of pipe is perforated along the top and sealed at both ends – one seal is attached to a small speaker or frequency generator, the other to a supply of a flammable gas (propane tank). The pipe is filled with the gas, and the gas leaking from the perforations is lit. If a suitable constant frequency is used, a standing wave can form within the tube. 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. Where there is oscillating pressure due to the sound waves, less gas will escape from the perforations in the tube, and the flames will be lower at those points. At the pressure nodes, the flames are higher. At the end of the tube gas molecule velocity is zero and oscillating pressure is maximal, thus low flames are observed. It is possible to determine the wavelength from the flame minimum and maximum by simply measuring with a ruler.
Since the time averaged pressure is equal at all points of the tube, it is not straightforward to explain the different flame heights. The flame height is proportional to the gas flow as shown in the figure. Based on Bernoulli’s principle, the gas flow is proportional to the square root of the pressure difference between the inside and outside of the tube. This is shown in the figure for a tube without standing sound wave. Based on this argument, the flame height depends non-linearly on the local, time-dependent pressure. The time average of the flow is reduced at the points with oscillating pressure and thus flames are lower.
Heinrich Rubens was a German physicist born in 1865. Though he worked with better remembered physicists such as Max Planck at the University of Berlin on some of the ground work for quantum physics, he is best known for his flame tube, which was demonstrated in 1905. This original Rubens’ tube was a four-meter section of pipe with approximately 100 holes of 2mm diameter spaced evenly along its length. 
When the ends of the pipe are sealed and a flammable gas is pumped into the device, the escaping gas can be lit to form a row of flames of roughly equal size. When sound is applied from one end by means of a loudspeaker, internal pressure will change along the length of the tube. If the sound is of a frequency that produces standing waves, the wavelength will be visible in the series of flames, with the tallest flames occurring at pressure nodes, and the lowest flames occurring at pressure antinodes. The pressure antinodes correspond to the locations with the highest amount of compression and rarefaction.
Gathered, written, and posted by Windermere Sun-Susan Sun Nunamaker
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