Here's what you need: One mug of hot coffee in a ceramic mug. One spoon. 1) Swirl coffee with spoon as if you are stirring in sugar or milk for thirty seconds. (In fact, feel free to actually swirl in sugar or milk. It makes no difference.) 2) Start quickly tapping the inside bottom of the mug with the tip of the spoon. 3) Observe the change in pitch of the tapping. Why does the pitch go up? It doesn't matter whether the liquid continues to swirl or not. You can stop the swirl of the coffee with the spoon and the same change in pitch is observed. Why?
I blame physics, although personally, I doubt my skills there. It pitches up because it's about to brake. If you continue like that, it might just do that. If I'm right, this experiment will have the same results if you don't have a liquid. If I'm wrong it will be a big FAIL from my side and I'd laugh. I'm too lazy to try it out at midnight, though.
Are we holding the cup or is the cup sitting freely on a table? Does it work with warm or cold coffee as well as hot coffee? It could be caused by contracting or expanding on the part of the mug. I'll have to try that out. Thanks Wrey, I love science experiments. Especially if it involves coffee.
It works whether the mug is being held, or set on a flat surface. I have never tried it with cold liquid. It only happens after the hot liquid has been swirled.
Another question. Did you try this just after pouring the hot coffee into a cold mug? If so, I'm assuming the mug would have one pitch when the atoms are slightly expanded (as they would be in a cool cup) but since the cup is rappidly heating, the cup is in the process of contracting and the pitch would become higher, right? I still haven't tested it, so this may be completely wrong. Look at those lipstick kisses on your face! What's been going on Wrey?
It is a phenomenon of psycho-physics. Yes, the perception of the pitch does indeed change but the actual pitch remains steady. You see, when coffee addicts anticipate the caffeine rush, it causes capillaries throughout one's body to dilate, much the same as an adrenaline rush. This capillary dilation increases the fluid pressure in the inner ear, resulting in a change in pitch due to fluid pressure. This is a dangerous condition that could lead to bleeding from the vestibular system, ruptured cochlea, broken ossicles (ear bones) and, in extreme cases, mental retardation. The cure is to drink the damn coffee instead of playing with it! LOL
It takes time for the heat of the coffee to travel through the walls of the mug. As the cup warms, it resonates at a higher pitch. Before you stir, the layer of coffee on the inside surfave of the mug is cooled slightly by conduction from the cooler mug. Stirring the coffee keeps te inner surface warmer, and speeds up the transfer of heat through the wall of the mug.
^This from a man who confesses that coffee smells like puppy pooh to him. (so...ignoring Saulty) It's what Cogito said...I was right then?
Except that most solids expand as the temperature rises. They do not contract (with some exceptions). But some materials still vibrate at a higher pitch when warm, including te ceramics coffee mugs are made from.
Now, here's the kicker. If you take the exact same same mug of coffee, without reheating it, and swirl the coffee again, the pitch will go back down to the original level and the process will start again. Technically, the mug is now minutely cooler than at the beginning of the experiment. Why would the process begin again? 'Splain me, Lucy.
Oh, right. I got it completely backwards. Arg. Cold contracts, heat expands. Edit: Wrey, you should write a book called "101 Fun Ways to Waste Time When You Work From Home: with step-by-step how-to guides for science experiments, refurbishing projects, and great recipes for guacamole!"
Squee!!!! I'll make a ba-jillion bucks and invite everyone from wf.org to my lavish Spanish Colonial Villa in the mountains of Puerto Rico where we can tap fresh coffee to our heart's content. (Shuttles will leave every hour from the villa down to the beach. Mojitos will be served on the shuttle, free of charge)
The same "skin effect" on the inside surface of the mug. the outside of the mug cools faster in air, so te outer wall of the mug is again cooler than the coffee. Stirring again speeds up the heat transfer. The final pitch is now lower than it was after the initial stirring due to the lower final temp. Another factor may be that the surface of the mug has a high surface tension, so the expandion of the bult of the ceramic increases the surface tension in the ceramic as it heats up, resulting in the pitch increase. Thhis same surface tension effect is what makes cracks and scratches grow with temperature changes, and also is how tempered glass is strengthened (well beyond the scope of this thread).
I just had this picture of different peoples, of different colors, genders, races, and religions all tapping their delightfully varied mugs of coffee, chai, or tea listening to the enchanting change in pitch of their respective mugs. It was a very multicultural experience....
I didn't need to. I've heard the sound enough times I was able to play it back and listen to it in my head. Good question though, Wrey. I had to think it through for a couple minutes.
I just tried the experiment with a translucent cobalt blue mug and got an unpleasant clanking sound with no variance. I'm pretty musical, so I think I would have recognized the change in tone. I'll have to try with a different mug. I suppose that was technically a 'glass' in the shape of a 'mug'. Perhaps it only works with ceramic?
Makes sense. The thernal conductivity and the specific heat (heat capacity) of ceramic vs glaas differ greatly, and that would definitely be important.
