Beats feature in my talks. The talk this time will have a new audience participation time, with whistling lollipops given to each member of the audience. We will try and make a beat frequency together.
The first thing I found on IOPSpark was a SPT classroom activity using audacity. There is a nice way to use audacity with a police whistle to explore ghost frequencies.
What never ceases to amaze me about physics is when you look at a concept you will always find an application for it somewhere!
To test for poisonous gases in mines they used to have organ pipe with surface air in it and another with air pumped up from the mine. These pipes of same length were played together. If one pipes frequency was changed due to the gas from the mine being of a different density then a beat was heard.
We used to use beats to tune our cornets in Frodsham Silver Band.
This tube is sometimes called a Herschel-Quincke tube (HQ tube). Usually it is the second name in the double named phenomenon that is lost over time, like Lorentz-Fitgerald contraction. Like I said above with the application of beats in finding poisonous gases in mines. Every time you look in to an effect or phenomenon in physics you find someone has made use of it. I discovered that the HQ tube is used in jet engines to try and remove certain frequencies that are much loader spikes than the general engine rumble.
You can hear with the same amount of water in each bottle the same tone. I am using an effervescent powder.
At 0.40 seconds in the video I blow across the top of the fizzing bottle and you can it does not really resonate as the bottom surface is no longer reflecting the sound from a smooth plane surface. It is important to let the water settle down. Now you have one bottle filled with carbon dioxide and one with air. The more dense carbon dioxide gives a noticeably lower tone.
When you blow across the top of the bottle you compress the gas and the gas springs back like a mass spring system. The denser gas moves backwards and forwards slower. The equation for the speed of sound (compression rarefaction) in an ideal gas is