Coriolis Effect (Jennifer Kim)

Author

Principles

Coriolis Effect
Foucault Pendulum

Standards

HS-ESS2-2 Analyze geoscience data to make the claim that one change in the Earth's surface can create feedbacks that cause changes to other Earth systems.

HS-ESS2-4 Use a model to describe how variations in the flow of energy into and out of Earth's systems results in changes in climate

HS-ESS2-6 Develop a quantitative model to describe the cycling of carbon among the hydrosphere, atmosphere, geosphere, and biosphere

Materials needed

There are companies that have demonstration equipment that also illustrate Coriolis Effect such as Flinn Scientific. The one that is highlighted on this page is no longer manufactured.

Procedure

Coriolis Effect-Northern Hemisphere1. Raise the end of the guide bar from its storage position, pivot it over the center post and press into position on top of the post.

2. Place the unit on the stage of the overhead project or the Elmo and project the demonstration equipment onto the screen.

3. Orient students by explaining that they are observing the earth as if they were out in space looking down directly over the North Pole.

4. With the marking pen along one side of the guide, draw a straight line on the map from the North Pole to the equator without moving the map. Explain to the students that this straight line would be the path of a moving object from the pole to the equator if the earth were not rotating.

5. Ask student what effect the earth's rotation would have on the path of an object moving from the Pole to the equator.

6. To test the student hypotheses, rotate the map in a counterclockwise direction as indicated by the arrows along the edge.

7. While rotating the map with one hand, draw a straight line with the other by running the marking pen along one side of the guide from the center outward.

8. Point out to the students that the guide was used to draw a straight line. Students will see that the line drawn while the map was rotating is curved or has a sidewise drift in relation to the earth.

9. The students should develop the concept that in the Northern Hemisphere, the curve is always to the right as you look in the direction of the object's movement.

Foucault Pendulum Over the North Pole

1. The guide bar should be swung away from the center post to its storage position.

2. Insert the snap-in fitting on the base of the pendulum mount into the hole at the edge of the map. The pendulum bob should rest over the North Pole, slightly above the poast.

3. Place the unit on the stage of the overhead project or the Elmo and project the demonstration equipment onto the screen.

4. Turn the map so North America is located at the bottom of the screen. Set the pendulum in motion, swinging in a north-south direction relative to North America (vertically on the screen).

5. Next, slowly rotate the map 90 degrees in a counterclockwise direction as indicated by the arrows along its edge, simulating the rotation of the earth.

6. At this point the swing of the pendulum will be east-west relative to North America even though the pendulum is still swinging in the same plane (vertically on the screen).

7. Point out that to a person sitting on the map in North America the pendulum has changed its direction of swing from north-south to east west, its apparent change of plane caused by the earth's rotation.

8. Ask students what the apparent direction of the pendulum's swing would be if the earth (map) were rotated 180, 270, or 360 degrees.

Explanation

A) Coriolis Effect

According to Newton's Law of Motion an object will continue in uniform motion in a straight line unless acted upon by a net outside force. In the diagram below it appears that this law has been violated. The solid line represents the path of a missile fired due south toward New York from the North Pole. When plotted on a map the flight path of the missile is curved to the west. It is not straight as the first law of motion demands. The missile lands not in New York but near Chicago.

Jennifer Kim, Van Nuys High School

The answer to this paradox lies in further consideration of the phrase "in a straight line" in the first law of motion. "Straight" in reference to what? If the path of the missile were plotted using only stars as reference points, the path would be seen as a straight line. To persons on the spinning earth the path of the missile appears to curve because their reference points are on rotating circles of latitude and longitude. In Diagram 1, the earth rotated out of position in relation to the missile passing overhead, but the missile remained on a straight path. The apparent curved path or sidewise drift of anything moving over the earth's surface is known as the Coriolis Effect after the French physicist, Gaspard Coriolis, who first explained it. The effect is entirely to the earth-bound observer using the rotating earth as a frame of reference. A mass of air, water or any other object moving over the Northern Hemisphere is deflected to the right of its path relative to the earth. In the Southern Hemisphere a moving object is deflected to the left of its path (Diagram 2). From this it can be inferred that, other factors being equal, rivers in the Northern Hemisphere will undercut their right banks more than their left banks and observations bear this out. The reverse is true in the Souther Hemisphere.

Since the earth's rotation deflects moving masses of air (winds) it has a profound influence on the world's weather. Without this whirling effect winds would blow straight from high to low pressure areas. Instead, they veer off to one side or the other resulting in strong prevailing winds that sweep diagonally toward or away from the equator instead of perpendicular to it. Diagram 3 illustrates the generalized wind patterns at the earth's surface, showing the Southern Hemisphere to have a pattern essentially the reverse of the Northern Hemisphere. The earth's rotation, its winds and the sun's radiant

energy are the primary factors controlling the circulation of the ocean currents. This combination produces a general pattern of clockwise surface currents in the Northern Hemisphere and the counterclockwise surface currents in the Souther Hemisphere (Diagram 4)

B) Foucault Pendulum-Proof of the Earth's Rotation

The first widely accepted experimental proof of the earth's rotation was provided by the pendulum experiments of French physicist Jean Foucault in Paris in 1851. From a ceiling more than 60 meters high he suspended a pendulum consisting of a steel wire with a cannon ball at one end.

The pendulum was drawn back and set in motion in a north-south direction. Applying Newton's First Law of Motion, a free-swinging pendulum will always oscillate in the same plane unless subject to a net outside force other than gravity. In spite of this, Foucault's pendulum slowly rotated tracing the plane of tis swing in a layer of fine sand on the floor. Eight hours later, it was swinging in a east-west direction! Foucault reasoned that the pendulum had not changed direction, but rather the earth had turned beneath it causing an apparent change in direction of the pendulum's swing.

Questions

Inculde at least three questons (with answers) that you can ask to assess understanding of the principles ilustrated
Question
Question

Everyday examples of the principles illustrated

1. The Coriolis Effect would help to explain the global wind patterns in the Northern and Southern Hemisphere2. The Coriolis Effect would help to explain why hurricanes always run in a counterclockwise direction in the Northern Hemisphere but run in a clockwise direction in the Southern

Hemisphere.3. The Coriolis Effect would help to explain why water drains differently in the Northern and Southern Hemisphere

4. The Foucault Pendulum demonstrates the Earth's rotation.