Thursday, March 15, 2007

The Mpemba effect and the Coriolis effect

Rules of Thumb rule!

The Dilbert Blog had a “rule of thumb” today that discussed the Coriolis effect today, and the allegation that water runs out of a sink in a different direction when south of the equator.

Scott Adams rule-of-thumb is to discount any scientific asertion where anyone chalenges to scientific proof:

"I’ve noticed that whenever there are two sides of an issue that sound like this…

1. The fact is true
2. The fact is complete bulls**t…

…you can safely bet that the fact is complete bulls**t."

Ha! Scott and I think alike, but it's interesting that something so ubiquitous could be disputed . . . .

My experients on the Coriolis Effect

I was at the equator a few months ago, and witnessed a “demonstration” of the alleged "Coriolis Effect" at a roadside show on the equator, and it’s quite an interesting “myth”.

She said that a simple, repeatable proof can show the fact that water drains in a different direction in each hemisphere (I'm always suspicious of proofs).

At equatorial sites in South America (Brazil and Ecuador) they commonly have a pail of water and a wash basin so skeptical folks can test the Coriolis Effect for themselves.

The rigged “proof” started at the exact equator where the water drained straight down without a vortex. Fifteen feet into the southern hemisphere, the water circles clockwise. And 15 feet into the northern hemisphere, the water circled counterclockwise.

In this case, like many scientific proofs in the real world, their “proof” was rigged! See my notes on the Coriolis Effect, for the whole truth.

Anyway this discussion led to a discussion about counterintuitive results like the Mpemba Effect.

Inside the Mpemba Effect

Back in the days of the ancient Greeks, Aristotle wrote about a strange event where hot water froze faster than cold water:

"The fact that water has previously been warmed contributes to its freezing quickly; for so it cools sooner.

Hence many people, when they want to cool hot water quickly, begin by putting it in the sun. . ."

This is called the "", a counterintuitive “fact” that hot water can freeze faster than cold water, but not always . . . .

That’s why science needs “rules of thumb”. Nothing is ever absolute in the real world, and it’s naïve to think that pure science can establish pure rules to govern any situation.

The real world is driven by probabilities, and the real scientists know that only the predictive value of rules of thumb have value.

This is especially true in predictive analytics, where historical data is used to predict future trends and signatures.