Was reading a good article in the new AOPA Flight Training about high altitude air currents, the 500 mb altitude, and movement of high and low pressure regions.

The topic turned to: If a high is centered over Florida, and a low is centered over Michigan, why doesn't the air flow directly north to south from H to L? The reason is Coriolis force, influencing the air mass eastward as it moves north.

Then the author said that Coriolis force doesn't affect the direction of cyclonic air movement, contrary to what is commonly believed. Draining toilets and bathtubs don't actually rotate the other direction in the southern hemisphere. Thermals and tornados neither.

His reasoning is that Coriolis force is weak, and these events aren't sustained long enough to be affected.

What say you?

Last toilet I used in the southern hemisphere was a bamboo chute that terminated in a pig pen. I don't remember whether the waiting pigs were milling left to right or right to left...

Well I'll be.....I always believed this but after looking it up on Wikpedia I stand corrected! Toilets and sinks are not affected! It's an urban legend! Shoot....what else do I absolutely, positively know that is false?

Zane - I think I don't know how to fly now - its your fault!

Skystrider wrote:Well I'll be.....I always believed this but after looking it up on Wikpedia I stand corrected!

I've been waiting so long for you to say that, Skystrider (about other less popular topics!)

I always thought the myth was true as well and have even argued it with a few people, who in my defense, had never pondered the concept of coriollis at all.

OK Zane. I went to the sink in my apartment here in Melbourne and tried it 4 times. The water always spun counter-clockwise. I never tried it at home so I don't know which way it goes in Oregon.

OK. I will bite...
I have never seen a High pressure area spin counterclockwise... and for that matter I haven't seen a hurricane spin clockwise.. Maybe I am missing something..

Flame suit on Scotty. .. :<)

Seems to me that the little whirlpool in the tub make the rubber ducky go around clockwise here and the man says counterclockwise in Oz. I remember checking it when I was down there and it was backwards to what I was used to. Just checked and the toilet spins counter and the sink spins clockwise. The toilet has no choice in the matter as it has directional jets under the rim that force the rotation but the sink does what it does naturally.

So what's up doc????

1SeventyZ wrote:Then the author said that Coriolis force doesn't affect the direction of cyclonic air movement, contrary to what is commonly believed. Draining toilets and bathtubs don't actually rotate the other direction in the southern hemisphere. Thermals and tornados neither.

What say I? Well, I agree that Coriolis force due to the earth's rotation is so small doesn't apply to small-scale phenomenon, but I'm very skeptical about it not applying to weather systems.

Let's say you have a 980mb low over MI and a 1030mb high over FL. That's only a 104psi difference over 1000 miles or .00002psi/ft! Assuming a 50mph wind somewhere in the middle, the Coriolis force is about .0001lb for a 1lb blob of air. The forces are small, but between the two Coriolis is the larger one.

I'm just applying engineering concepts to meteorology, so I could be missing something huge. I hate to reject an idea just because it doesn't fit into my concept of reality without fully understanding what is being said, so how does he explain cyclonic circulation?

JRStripe wrote:
What say I? Well, I agree that Coriolis force due to the earth's rotation is so small doesn't apply to small-scale phenomenon, but I'm very skeptical about it not applying to weather systems.

To be clear, he upholds that Coriolis affects weather systems, but not tornadoes, thermals, or toilets.

Kenny Chapman wrote:OK Zane. I went to the sink in my apartment here in Melbourne and tried it 4 times. The water always spun counter-clockwise. I never tried it at home so I don't know which way it goes in Oregon.

Flush the toilet a couple of times... for science... which way does it flow? Ask your neighbors to flush theirs!

Now I remember seeing some science-y geographic-y show many years ago with some guy demonstrating water flowing down a drain near the equator and the water didn't spin at all.

The toilet here went counter clockwise (could be the way the water flows into it from the tank). One sink started off clockwise. Another counter clockwise. The water may have had slight motion.

Way to go Zane. You've just contributed to untold gallons of water being wasted worldwide.

1SeventyZ wrote:

JRStripe wrote:
What say I? Well, I agree that Coriolis force due to the earth's rotation is so small doesn't apply to small-scale phenomenon, but I'm very skeptical about it not applying to weather systems.

To be clear, he upholds that Coriolis affects weather systems, but not tornadoes, thermals, or toilets.

I'll buy what he's selling then. I thought he was proposing some sort of new science.

The formula for calculating Coriolis acceleration due to the earth's rotation is: Ac = 2WVsin(lat)
Where:
Ac = Coriolis acceleration = ft/sec^2
W = Earth's rotational velocity = rad/sec (.0000727)
V = velocity of object= ft/sec
lat = degrees latitude (North positive, South negative)

The angular velocity of the earth is so small that it dominates the equation. It's a good thing too. If it wasn't and you were flying a plane near the poles you would have to hold a Coriolis correction angle!

The force is there, but on a small scale it is overshadowed by other things. Like Shorton says, toilets have jets that force their rotation. Sinks have their own problems. Their drain is normally offset and the stopper sits cocked off to one side so the flow into the drain is not balanced . To really test the theory, you would need to eliminate the effect of the sink itself. A big round tank with a nicely radiused drain in the center would work.

Coriolis acceleration shows up in other places too. It affects anything that has both rotational and linear motion. Say you are doing a 2min turn at 120mph. Your pistons are feeling it. A 2lb piston has a Coriolis force of .25lb ish.

The concept is rooted in disparate angular velocities, right? If an object bridges latitudes, the latitudes closer to the equator have a higher angular velocity, due to the fact that the object on a path of greater circumference must cover more radians per unit time.

If there was no friction between the air mass and the surface of the earth, the air mass wouldn't be subject to uneven accelerations at different latitudes?

I'm having trouble visualizing the forces in your piston example, JR. You're saying the piston is undergoing a stronger centripetal force at the top of the stroke than the bottom of the stroke? Or that its angular velocity increases from the top to the bottom of the stroke, causing the skirt to rub the trailing surface more than the ring on the leading surface?

Head...hurting....

The concept is rooted in disparate angular velocities, right?

I think it's the other way around Zane. Everything sitting on the earth has the same angular velocity (360 deg per day), but objects sitting on the ground at the equator have a linear velocity of around 1000 mph while polar objects are rotating, but have hardly any linear velocity. The Coriolis "force" is really an effect, an apparent force, not a real one. It's an illustration of how complicated you can make things if you go to a rotating coordinate system and throw in spherical geometry to boot. If you are flying home from a great summer in Anchorage and aiming for San Francisco, SFO will have moved to the east before you get there. You will have to make control inputs to account for it, although, they will probably get lost in all the others you make during the trip.

The reason the toilet water doesn't react the same as rivers, ocean currents or low pressure systems comes down to time and distance. During the draining period, the earth doesn't move much and the water doesn't travel very far, so the contribution of the coriolis effect is hardly noticeable compared to vibrations from the truck driving by.

YB

You guy's are way over my head. I do believe there is Coriolis force though. This sounds silly, but if you try to force the water to rotate "backwards" in a swimming pool, the skimmer won't work well. It will rotate faster in one direction than the other. I thought it was due to Coriolis force.

Yellowbelly wrote:

The concept is rooted in disparate angular velocities, right?

I think it's the other way around Zane.

Ahh, agreed. I always get my v mixed up with my w.

Adding to what Yellowbelly said...

It’s a hard concept to wrap your head around because there aren’t that many things to draw parallels to that you can actually feel. The best example that I have heard is the merry-go-round one. If you walk from the outside to the center of a merry-go-round along a straight line you feel a force that pushes you off to one side. Now, imagine the earth is the merry-go-round and you are a blob of air… you feel that same force. It’s a lot smaller because the rotational velocity is less, but when all the other forces are small it has an effect. One thing to notice it the force is felt in a plane perpendicular to the axis of rotation, so it is strongest at the poles and fades to nothing right at the equator. That is what the “sin(lat)” term is doing in the equation.

Like Yellowbelly said, it is an apparent force and not a real one. That means that it is caused by acceleration and not by impact, a mechanism, or something. It is sort of an annoying bastard second cousin of centrifugal force. They are related through that law of motion that says things in motion stay in motion unless acted upon by a force. One does not cause the other though. Centrifugal force is caused by an object trying to maintain a straight path but being forced into a curved one. It is present in all rotation. The Coriolis force appears when an object tries to move along some path in the plane of rotation. It is present when rotation and liner motion are combined.

Maybe my engine example just made things more confusing. It was intended to point out that Coriolis acceleration is caused by things other than the Earth’s rotation. Maybe the merry-go-round analogy will clarify my poorly thought out engine example. It’s kind of stupid, but probably everyone has tried it... except for the curve ball part. Imagine you are watching two kids on opposite sides of a spinning merry-go-round tossing a ball back and forth. One tosses the ball directly to the other who misses it. You see the ball as going in a straight line, but the second kid rotated out of the way before the ball gets to him. The kids and their rotating frame of reference don’t see it that way. They think the ball has taken a curved path. To get the ball to the other person they might throw a curve ball. Now they think it has gone straight, but you see it curve. That sideways force caused by the curve ball is the Coriolis force. The same thing is happening to the piston in the engine. The cylinder is following a curved path because of the turn and the piston wants to go straight because of its momentum.

Good stuff!

For whatever reason, that explanation reminded me of how the British scientists calculated the age of the sun back in the late 1800's. They of course did the work based on the fuel they assumed the sun was using. And the best fuel they knew of was good old British coal. So, according to their calculations the sun could only be a few million years old because it must be burning coal!

Now since Darwin's theory of evolution would obviously take tens of millions of years to work it must be wrong! Ipso facto!

Skystrider wrote:For whatever reason, that explanation reminded me of how the British scientists calculated the age of the sun back in the late 1800's. They of course did the work based on the fuel they assumed the sun was using. And the best fuel they knew of was good old British coal. So, according to their calculations the sun could only be a few million years old because it must be burning coal!

Now since Darwin's theory of evolution would obviously take tens of millions of years to work it must be wrong! Ipso facto!

Hey! Gimme a break here! I talk with my hands, not my fingers. If you could have seen the gestering it would have been a lot better!

JRStripe wrote:

Skystrider wrote:For whatever reason, that explanation reminded me of how the British scientists calculated the age of the sun back in the late 1800's. They of course did the work based on the fuel they assumed the sun was using. And the best fuel they knew of was good old British coal. So, according to their calculations the sun could only be a few million years old because it must be burning coal!

Now since Darwin's theory of evolution would obviously take tens of millions of years to work it must be wrong! Ipso facto!

Hey! Gimme a break here! I talk with my hands, not my fingers. If you could have seen the gestering it would have been a lot better!

Ahhhh...your right! I just knew I was missing a key component!

Kenny Chapman wrote:OK Zane. I went to the sink in my apartment here in Melbourne and tried it 4 times. The water always spun counter-clockwise. I never tried it at home so I don't know which way it goes in Oregon.

Don't know about oregon, but here in Washington at about 48N 123W toilet operates clockwise. Of course, the Corvallis effect is stronger here as I'm only about 250 miles north of Corvallis.
When you said Oz has CCW toilet op's, were you looking down at it or inside looking up? (ya never know....)

Eric