Tuesday, March 02, 2010

Pitch drop experiment

Pitch drop experiment. One drop falls about every decade!

When I was a boy, I once found a big clump of pitch. It's really kewl. When it's at cool temperatures, it's hard and very brittle, like black glass, only opaque. But when it warms up in your hand, it becomes soft and mallable!


Alex said...

"it's hard and very brittle, like black glass, only opaque."

Would it not be easier to just say "it's hard and very brittle, like obsidian"?

Eolake Stobblehouse said...

Sure, but that depends on people, including me, knowing what it is! :-)

Aardvark said...

So in other words, it's pitch black!

Eolake Stobblehouse said...

Yup, thus the expression.

tarrymacadam said...

"To date, no one has ever actually witnessed a drop fall. The experiment is in the view of a webcam although technical problems prevented the most recent drop from being recorded."

Onward through the digital fog!

Pascal [P-04referent] said...

So... is that what they call a tar pitch? ;-)

What do you call it when a drop does drop?

Why the battery next to it?

That pun was crystal clear. :-)

My father's an engineer. He's told me about this, oh, probably 2 or 3 drops ago. ;-)
Pitch behaves like a solid, but you can also consider it as a highly viscous liquid. Which reminds me of a still not quite settled debate on this very blog about glass.
Non-crystalline bodies gradually become less viscous when heated, until they finally melt for good. Think of wax. Everybody has played with wax...

I still believe that glass is just even more viscous, maybe some 100-1,000 times more than pitch. Which itself is about 230 billion times more viscous than water, so it's not inconceivable...

On the other extreme, supercold helium, about 2.6 degrees or less above absolute zero if I memory serves, is still liquid, and doesn't seem about to turn solid, because in fact it becomes hyperfluid. It would seem its viscosity ACTUALLY becomes zero. Quite fun to play with,in its own way.
A result of it is that no open recipient can keep it. Porous ones such as porcelain, no matter how thin the pores, see the tiny helium atoms leak through them like warm water through a stainer and spread on the floor in a puddle. Non-porous recipients, well, they display a funny capillarity phenomenon. An atom-thin film of helium climbs the surface, unhindered by viscosity, goes down on the outside, and then the siphon force empties the whole recipient over time.

That above experiment, made with hyperfluid helium, would probably last only as long as the effect of gravitational acceleration!

"To date, no one has ever actually witnessed a drop fall."
Just. Don't. Blink.
Alas, no staring contest champion can hold THAT long!
A snake or fish could, because they have no eyelids. But they still do sleep...

P.S.: I knew what obsidian was. :-)

Speaking of speeds... my verif advises for a "porshe"!
I should be able to pay for it in a few drops' time. ;-p

Eolake Stobblehouse said...

"An atom-thin film of helium climbs the surface, unhindered by viscosity, goes down on the outside, and then the siphon force empties the whole recipient over time."

I heard about that, decades ago. I never understood why and how it climbs up, though.

Pascal [P-04referent] said...

It climbs by capillarity, which is a force of attraction to the support making the liquid spread on it. [Mercury for instance doesn't spread, it has a negative capillarity to glass.] Superficial tension (another attraction force) holds the film together and causes the siphon effect. The film is because the attraction has a very short range, doesn't gather the whole bunch into a clump.
But there is no FRICTION, thus no viscosity. Friction is not the same as attraction. A spherical magnet rolling on a steel plate had great attraction, but creates no friction (= resistance to sliding).
Now, adhesion, that would be attraction and friction combined. Such as in succion cups of stickers.

I wouldn't say my here image explains what actually happens with hyperfluid helium. I think it has to do with quantum physics. Therefore very complicated mathematical formulas which can hardly be explained with classic images.
But I've read that helium nuclei have a VERY strong magnetic momentum. So, just imagine a buch of tiny sphere magnets all coated in super Teflon and motor oil, and rolling together. A lot of attraction, but zero friction.

Makes sense?

Eolake Stobblehouse said...

I think so, thanks.

Pascal [P-04referent] said...

Well, that makes one of us then. ;-)