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Erdinger's equation

Thursday 31 July 2014

It's been a superb summer up until now so I have been able to enjoy a few evening beers on the balcony. During one such evening I became interested in the motion of the bubbles rising to the top of the glass. This is beginning to sound like the sort of EE introduction I am always telling my students to remove. I used my mobile to record the bubbles so that I could do some analysis. As you can see I held my mobile sideways. I often do this, it had nothing to do with the content of the glass.

Eventually I got round to analysing the video which might have something to do with the deterioration of the weather these last couple of days. The motion of one bubble is shown below.

You can see that the bubble seems to have a fairly constant velocity to start then accelerates at an increasing rate. My hypothesis is that at the beginning the bubble moves up the side of the glass so the motion of the bubble is restricted. After it breaks away it accelerates. One might expect that the acceleration would get less as the drag force got bigger but can there be drag on the motion of a bubble? What forces are actually involved here?

Another interesting aspect is the way the bubbles get bigger as they rise. This is even noticeable on the animation here. Are they really getting so much bigger or is it due to the distance from the camera or magnification by the lens of beer? Some great EE and Investigation possibilities here. The beer was of course Erdinger.

Tags: bubbles, EE, investigation


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