Coriolis Model

Turnabout is fair play

Introduction

Coriolis forces can be modeled using a rotating transparency.

Material

• The template shown below.
• A piece of cardboard larger than the template. (Eight-and-a-half by eleven paper (A5 paper)
• A transparency as large as the template.
• A water erasable pen.
• Transparent tape
• A thumbtack.

Assembly

Tape the template to the cardboard.

Center the transparency over the template.

Put the thumbtack through the center of the transparency into the + marked on the template.

Make a mark on the transparency at the 0 mark in the arc of dashes.

To Do and Notice

Notice that straight line rows of dots labeled 1 through 5 radiate out from the central + on the template.

Rotate the transparency so that the mark moves counterclockwise from the 0 to the 1.

Use the pen to mark all of the dots labeled 1 on the template.

Rotate the transparency so that the mark is over the 2.

Use the pen to mark all of the dots labeled 2 on the template.

Continue until you have marked all 5 numbers.

Remove the transparency and examine the pattern of dots.

Notice that even though in the frame of reference of the template the dots are in a straight line, they all make arcs on the transparency.

As one moves out from the center the dots on the transparency arc to the right.

Going Further

Use a new transparency.

Put the thumbtack through the center of the transparency into the + marked on the template.

Make a mark on the transparency at the 5 mark at the bottom of the arc of dashes.

Use the pen to mark all of the dots labeled 5 on the template.

Rotate the transparency so that the mark is over the 4.

Use the pen to mark all of the dots labeled 4 on the template.

Continue until you have marked all 5 numbers.

Remove the transparency and examine the pattern of dots.

Notice that even though in the frame of reference of the template the dots are in a straight line, they all make arcs on the transparency.

As one moves in toward the center the dots on the transparency arc to the right.

What's Going On?

In the rotating frame of reference the straight line motion appears to curve to the side.

To make an object curve to the side physicists know that a force is necessary. They create a force known as the coriolis force to explain this curve.

So What.

When viewed from above the north pole the earth rotates counterclockwise.

Air flows radially outward from a high pressure area.

So air moving outward from high pressure areas in the northern hemisphere is deflected to the right. The high pressure area thus rotates clockwise.

Air is forced in to the center of a low pressure area.

So air moving inward toward a low pressure areas in the northern hemisphere is deflected to the right. The low pressure area thus rotates counterclockwise.