# Hello everyone, first time post here. Before the question, a brief

1. Aug 22, 2010

### shdw

Hello everyone, first time post here. Before the question, a brief background:

Intro:
My name is Brian and I am a flight instructor with a BS in aviation flight operations. I enjoy science in general and study it on my own time for fun. That said, my science background is still meager so be gentle with your answers. Thank you.

Question:
I am familiar with Coriolis and have seen a variety of explanations. The most common is that of two kids on a merry go round throwing a ball. What I am looking for is more ways to explain it.

That said, assume you are teaching an 8th grader 1 on 1 what Coriolis is. This person would be interested in being a pilot. They may or may not have a technical background, so it can be assumed they know nothing of, about, or related to Coriolis. How would you present Coriolis to them?

Thank you in advance for the assistance,

~Brian

2. Aug 22, 2010

### Feldoh

Re: Coriolis

I remember a few years ago I read this on wikipedia:

"The Earth's rotation causes the surface to move fastest at the equator, and not at all at the poles. A bird flying away from the equator carries this faster motion with it—or, equivalently, the surface under the bird is rotating more slowly than it was—and the bird's flight curves eastward slightly. In general: objects moving away from the equator curve eastward; objects moving towards the equator curve westward."

I think that it is a good explanation.

3. Aug 22, 2010

### Dr Lots-o'watts

Re: Coriolis

If you have a turntable that is turning counter-clock wise, you can view it as the earth viewed from above the north pole (spinning eastward).

Fix a piece of paper on it, and make it spin. While it's turning :

1. Draw a strait line from the center towards a fixed point on the base.

2. Draw a strait line from a point on the circumference towards the center.

3. Draw a strait line in any random direction (provided it is a straight line relative to the walls in the room).

If you stop the rotation, you will note that the lines on the paper are curved, always towards the right.

The apparent force towards the right that is perceived by a crawling bug on the spinning turntable is the coriolis force. Since it is related to its inertia, it is zero if the bug is at rest (only the centrifugal would remain), and it gains magnitude with speed.

4. Aug 23, 2010

### Cleonis

Re: Coriolis

Well, for aviation the thing that is relevant is the http://www.cleonis.nl/physics/phys256/coriolis_in_meteorology.php" [Broken]. This link is to an article on my website. The article is illustrated with animations.

The example of throwing a ball while riding a merry-go-round is quite limited in scope. There's more to it; for you as an aviation instructor I think it'll be worthwile to go and see what is taken into account in meteorology.

Last edited by a moderator: May 4, 2017
5. Aug 23, 2010

### Cleonis

Re: Coriolis

There is a problem with the above "explanation".

We have the law of conservation of angular momentum:
If you are circumnavigating a central axis, and your distance to the central axis becomes smaller, then your velocity increases. Let me call the initial velocity and the initial radial distance v1 and r1 and the final velocity and radial distance v2 and r2.
Conservation of angular momentum:

$$v_1 r_1 = v_2 r_2$$

This says that if the radial distance is halved the velocity is doubled.

In the "explanation" that you quoted the suggestion is that the precise velocity an object has when co-moving with the equator is carried over unchanged when moving to another latitude. That's not the case.

Of course, things would be really bad if that wrong explanation would predict the opposite of what actually happens. While the explanation is wrong, at least it gives the correct direction of the effect.

But there's a larger issue. The suggestion is that the case (bird starts from equator, moves to another latitude) is a case of conservation of linear momentum. But what actually applies is the law of conservation of angular momentum.