Freestetter's world of formulas: Why don't you spill the coffee as you walk backwards
Without coffee there is no mathematics: it is almost a law of nature. But what do you do if the creativity-boosting liquid can't be transported without incident?
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It is easy to spill coffee while walking. But there are tricks to avoid this.
“We can rarely hold coffee without spilling it once.” When you start a sports article with a sentence like this, you know it's worth reading. And it actually is “A study on the phenomenon of spilling coffee in a low-impulse system” By Jiwon Han A treasure trove of great information.
The phenomenon examined there is well-known: if you carry a cup of coffee from point A to point B, the drink tends to spill. This problem must have a cause, and perhaps also a solution. The way to get there is through this formula:
It's surprisingly complicated considering it's just a cup of coffee. But if you not only consume the beverage of choice for research, but also look at it scientifically, it is a liquid that can interact with the movement of the cup in very complex ways. It is precisely this reaction that can be best understood using the formula. Without going into details, it describes the natural frequency of a fluid in a cylindrical vessel. In other words, the cyclic movement that occurs when coffee is left to its own devices after being stimulated from the outside. But if other stimuli come from outside – and at a period that matches the natural frequency (or a multiple of it) – the movement of the coffee can increase until what we all know happens: it spills over the rim of the cup.
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Jiwon Han looked at these natural frequencies and compared them to the vibrations created when you hold a cup of coffee. With the typical dimensions of a cup of 95mm high and 82mm in diameter, you get a natural frequency of around 4Hz. This exact frequency can be found in the movement of the hands during normal walking, as Hahn discovered in related experiments. So it's no wonder it's so easy to pour over coffee.
By identifying the problem, you can easily find a solution. For example, you can walk backwards. The unusual movement makes you move your hands differently than before and the natural frequency of the coffee cup is no longer stimulated. Unfortunately, this does not reduce the risk of spillage. Especially if we're all carrying our coffee backwards around the place from now on. But you can also hold the cup in a different way, in the form of a “claw hand,” Hahn explains. Instead of using the handle, you hold the cup by the top with your fingers and this also prevents natural frequency stimulation.
Red wine instead of coffee
This solution is very practical and much less obvious than reverse gear. If you still don't want to go without transporting the coffee as usual, you will have to switch to a different container to prevent spillage. The natural frequency depends, among other things, on the radius of the cup; The smaller it is, the higher the frequency and the more difficult it is to stimulate while walking. For example, you can drink coffee from test tubes, but this is somewhat hesitant in most laboratories.
Or you can leave the coffee alone. In his work, Jeewon Han also examined how red wine behaves in a typical wine glass. At 4 Hz, it moves back and forth slightly in the glass without spilling anything. But if red wine were consumed in the same amounts as coffee, it would likely have little benefit for athletic creativity. W: Yes, you can of course just use a cup with a lid. But where is the sporting fun in that?
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