Apparently Peter McLeary, the Bad Coriolis tourist scam artist in Nanyuki, Kenya, isn't in too shabby of company. His claim that mis-states the direction of the Coriolis Effect in each hemisphere was also made by none other than Dr. Isaac Asimov, in his book, "The New Intelligent Man's Guide to Science" in it's second publishing in 1965.

Lest you think Dr. Asimov's malaprop was just a typo, twice in the same book, on both occassions that he discusses the Coriolis effect (pp. 94 & 104), he states that the effect is CLOCKWISE in the Northern Hemisphere, and COUNTERCLOCKWISE in the Southern. In the second mention, he even gives it as a cause for the direction of the clockwise Gulf Stream ocean currents of the Norhtern Atlantic--so he must have meant it!

So, even one of the most beloved science (and science fiction) writers of all time can get it wrong every now and then.

Now, with a little speculation, we might even be able to point to Asimov as the cause of Peter McLeary's error. That is, his error of Coriolis direction, not his error of scale and magnitude.

In the days before good Internet search engines and content, the best place to read about the Coriolis Effect would be in a physics textbook. If you didn't have one of those, a more accessible source might have been the very popular above-mentioned book published by the famous Isaac Asimov, available in almost every library in the world.

Perhaps Peter McLeary is an Asimov fan!

And perhaps now we know. . . the rest of the story.

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Paul Smith

Asimov seems to be right, though. Clearly, a north moving projectile in the northern hemisphere would experience a tendency to move eastward to its right, which is clockwise. It depends upon the phenomenon, and how you observe it. If you look at a basin, draining from its edges to a hole in the center, the particles--as they enter the counterclockwise vortex--also move to the right.

Grapes - Interesting point about projectiles. I hadn't looked at it that way.

However, Asimov clearly is not talking about the direction of projectiles. In fact, he specifically addresses the Coriolis effect on air masses and the CLOCKWISE twisting motion of hurricanes and tornadoes it produces in the Northern Hemisphere. So, I still think he just got it backwards.

P.S. Dr. Plait - since I forgot to mention it. . . great book! I really enjoyed it and did learn a lot that I hadn't seen on badastronomy.com.

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Paul Smith

Wouldn't the clockwise/counterclockwise rotation depend on whether you're observing the mass of air from above it or below it?

Well, it is true for the Gulf Stream anyway. What does he say about the hurricanes and tornadoes?

Chuck - Yes, it would matter. But, in all these cases, the assumption is that you are viewing it from above, like from a satellite.

Grapes - Here are some exact quotes. See if you interpret them any differently than I did.
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p. 94 "The effect of such Coriolis effects on air masses is to set them to turning with a clockwise twist in the Northern Hemisphere. In the Southern Hemisphere, the effect is reversed, and a counterclockwise twist is produced. In either case, 'cyclonic disturbances' are set up. Massive storms of this type are called 'hurricanes' in the North Atlantic and 'typhoons' in the Northern Pacific. Smaller but more intense storms of this sort are 'cyclones' or 'tornadoes.' "

p. 111 ". . . the ocean currents have been thoroughly mapped. They move in large clockwise circles in the oceans of the Northern Hemisphere and in large counterclockwise circles in those of the Southern, thanks to the Coriolis effect (see page 94). "

Well, they're both right... sort of.

The Asimov quote:
This actually matches what Phil says in his book (look at the diagram on p 25). The confusion arises because we all seem to be taking this and applying it - not to winds, but - to a Low or High pressure system.

Unfortunately, Lows and Highs are a bit more complicated. ( http://itg1.meteor.wisc.edu/wxwise/m...ostrophic.html ) They are the result of three forces, one of which is Coriolis; the net result of those forces determines whether the system turns CW or CCW.

Asimov's quote doesn't get into these details and does leave the impression of a NH hurricane rotating CW; it actually moves CW and rotates CCW.

The other Asimov quote:
Which is true. ( http://www.oceansonline.com/ocean_currents.htm ) The surface currents are bent by the Coriolis effect (although some are also affected by gravity). Thus, the major NH currents (like the Gulf Stream) flow CW while the major SH ones flow CCW, the same as the major wind currents.

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<font size=-1>[ This Message was edited by: Jim on 2002-03-11 10:17 ]</font>

And the error had still not been corrected by 1984, when Asimov's guide was in its fourth edition, Asimov's New Guide to Science.

Incidentally, there's a similar misprint in Bad Astronomy, p 25. The penultimate word in the caption should read counterclockwise.

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- Learn a lot teaching others.

As Jim has shown, there is ambiguity in the published statements as the pressure gradient in the air masses are not addressed.

These is another site that is a bit more simple that is helpful in illustrating the air mass directions.

>>> Coriolis stuff &lt;&lt;&lt;

It is interesting that this site states that no work is done by the Coriolis force. I do not understand this since the missles, bullets or winds act on other bodies as they move eastward when they are directed from equator to north pole. Work is force x distance and distance appears to be a factor as it travels.

Would it be wrong or too unconventional to speak of the Coriolis Effect more in terms of an inertial force and that each latitude constitutes a separate inertial frame?

If so, objects traveling through these slower, or faster, inertial frames will be impacted by the inertia of the traveling object. Even if it's just air resistance that opposes the inertia you will have friction creating heat involving work and now even power. Right? #-o

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

This is unambiguously wrong, and it's the opposite of what Phil says in his book (p 25). Cyclonic disturbances (ie depressions or lows, including hurricanes) rotate counterclockwise in the northern hemisphere. I'm a big fan of Asimov, but special pleading won't save him here.

Thanks for the interesting link, George. I think the explanation of how the Coriolis Force does no work is that it only acts to change the direction of the air mass (or whatever). Imagine a mass of air is moving north from the equator. The Coriolis Force is directed towards the east, and so has no component in the direction in which the mass is moving.

This PDF, How Do We Understand the Coriolis Force? looks promising, but I haven't read it yet.

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- Learn a lot teaching others.

I'll have to admit you're right. I was trying to give him a little hope here as there is a slight chance he was refering to the air mass as a whole. The air mass he mentioned would get a clockwise twist if you just track the center. He may have overlooked the obvious view of the reader. But, he likely just messed up.

I am still struggling with the work issue. From the equatorial inertial frame of the air mass, it makes sense. No work would be done if it is seen to travel eastward relative to the higher lattitudes unless it slams eastward into slower air masses, then, isn't work done? I suppose I simply see the Coriolis Effect as a way to describe the effect that simple inertia will have has an object changes lattitudes. Am I missing something in this thinking?

If I travel in my car at 20mph and suddenly hit a telephone pole, isn't work involved. I'd guess about $2,000 to $3,000 worth of work.

So you see, I see it as a result of interaction with inertial frames.

Guess I should read that pdf too.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

How does this sound?

The inertia is simply regarded as kinetic energy as it impacts other inertial frames.

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Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

Saw this in The Guardian, today, Thursday November 13, 2003

The great plughole debate

"Does water really swirl in the opposite direction south of the equator? Well, yes and no, finds David Adam"

He mentions Kenya, 'charlatans' and 'gullible tourists'

This is just daft (and nothing to do with the article above!) ...Coriolis Cats...

We have two cats, sisters who don't get on, so they've taken a room each upstairs. One day I noticed that Pebbles in the NE facing bedroom was curled up nose pointing clockwise, while Ruby in the SW facing room was curled up nose pointing counterclockwise.

However, subsequent observations have failed to reveal a pattern to cats sleeping curled up clockwise or counterclockwise.

Also in this paper today, but on a different topic from this thread (should I post it elsewhere?): 'Tim Radford selects his all-time favourite science scams' - Too good to be true

Carolyn