Here's a physics question

Post by **Ryoki** » Wed Mar 08, 2006 8:55 am

I just got myself a hot cup of coffee and i noticed something peculiar: when you stir the coffee and tap your spoon repeatedly on the bottem of the cup, it makes a tapping sound that increases in pitch.

What causes this? I am mystified!

Post by **MKJ** » Wed Mar 08, 2006 8:59 am

added milk or sugar? its increases density of the liquid ysee, therefore buffering much of the sound.
same goes for when you stir it, the circular motion creates a vortex decreasing the center depth and therefore buffering less of the sound.

Post by **Ryoki** » Wed Mar 08, 2006 9:03 am

Yeah i put in some milk & sugar, this coffee machine makes a rather strong double espresso. So then, this wouldn't work with just hot water?

EDIT: oh wait, you're saying this would work with just water but the milk & sugar adds to the effect?

Post by **MKJ** » Wed Mar 08, 2006 9:07 am

water doesnt buffer as much as something like coffee would so the effect is probably too small to notice, but it should cause the same effect.
it also works with milk & nesquick

Post by **Ryoki** » Wed Mar 08, 2006 9:10 am

Heheh - okay then. Thank you sir, for your wise words. :icon14:

Post by **Eraser** » Wed Mar 08, 2006 9:13 am

I've noticed that with hot chocolate as well and I think the same effect can be noticed with plain water too.