Friday, January 21, 2011

Cat's Got Its Tongue

Capillary action and adhesion are things that always gets mentioned at the start of Gen Chem II, with the standard picture, and maybe even Eli brings a narrow tube in to show how water colored with laser dye gets pulled up and accompanied by the standard eye rolling in the audience. The physical reason for this is that the water has a stronger attraction for the surface of the tube than for itself, so it "attaches" and pulls itself.

Folks at MIT have the "Cat's Tongue" video. First look at the cat in action



Then look at the simulation



and then go back and look at the first video. Advanced students can peer at the end of the simulation and tell us why the column of water when it falls back to the pan, balls up.

And another video for those of you who want to see how the discoverer figured this out

13 comments:

Horatio Algeranon said...

Horatio has figured out the physics of cat napping (and practices it regularly)

In Hell's Kitchen said...

it balls up because of the capillary instability.

Horatio Algeranon said...

All this time, Horatio thought it was catillary action.

dhogaza said...

"Horatio has figured out the physics of cat napping (and practices it regularly)"

Unfortunately, I've never gotten the knack of catnipping ...

Rattus Norvegicus said...

I always thought that cats "lapped" by jumping up into yours when you sat down!

Anonymous said...

surface tension.

Lawyer Mouse
(who just finished his second semester of Gen Chem, as a prerequisite for sitting for the patent bar exam.)

EWI said...

Speaking of "cat's got its tongue", Richard Tol appears to have fallen off the face of the earth in the last number of days, a very un-Tol-like silence on the Internet.

The only reference I can find using Google's blog search is (yet another) Lomborg article, this time in the WSJ (subject can be guessed). Tol, of course, will as ever claim that "Lomborg misquotes me", his usual response to all of these tragic misunderstanding when his work is used by the denialists.

Horatio Algeranon said...

Cat lapping,
Cat sipping,
Cat napping
Cat nipping
Are so very very
Categorically catillary

EliRabett said...

The Lawyer wins.

Anonymous said...

The bit that I was intrigued by was the "fracture" of the fluid column (an approx. hemisphere in contact with a cone) and the position of the "fracture".

Cymraeg llygoden

In Hell's Kitchen said...

Eli, it's not just surface tension, it's geometry too. Therefore
what we're seeing is due to a nonlinear capillary instability.

EliRabett said...

Driven by?

Anonymous said...

Nice lot of quips on cats and capillary - but Eli, although the surface tension forces are stronger to glass than air (and so cause the curved meniscus) they don't pull the liquid up the capillary. That is atmospheric pressure pushing it up - the curved meniscus creates a lower pressure below the meniscus (surface tension effects again). Deceptively fortuitous algebra can 'prove' the pull, but a nice thought experiment shows the flaw. Think of a capillary as the stem of an inverted funnel dipping into the water - surface tension forces would have to hold up a huge mass of water, and they don't!

Ian