The Coriolis Effect Model

Introduction

The concept of the Coriolis Effect can be difficult to understand but this simple model allows students to see its effect for themselves.

Concepts

• Coriolis Effect
• Wind currents
• Ocean currents

Background

The Coriolis Effect, a term first introduced by French mathematician Gustave Gaspard de Coriolis (1792–1843), is the “imaginary” force that seems to deflect objects such as wind and storms over the surface of a planet. When viewed from above the North Pole, the Earth spins counterclockwise. Objects moving on or near the Earth’s surface are deflected to the right in the Northern hemisphere and to the left in the Southern hemisphere. This deflection would be apparent if an observer from space were to watch an object’s path along a straight line. The Coriolis Effect plays a major role on the movement of wind and storms but also on ocean currents and the flight paths of airplanes and missiles.

The Coriolis Effect is not the only factor influencing air and water movement, temperature also plays an important role. Surface temperatures on the Earth vary depending on global location. Since the Earth’s surface is curved rather than flat, not all areas receive the same amount of solar radiation (see Figure 1).

Because of this, the air over the equator is heated more than other locations on Earth. Since less radiation is received at the Poles of the Earth, the air there is cooler and more dense. As this dense, cool air sinks and moves along the surface of the Earth, it interacts with warm air creating pressure differences. These pressure differences and the Coriolis Effect create distinct wind patterns on the Earth’s surface (see Figure 2). They also lead to the counterclockwise rotation of hurricanes in the Northern hemisphere and the clockwise rotation of typhoons in the Southern hemisphere.

A similar situation is seen in the Earth’s oceans. Ocean water located near the North and South Pole regions is very cold and dense. The dense water at the pole regions sinks to the ocean floor and flows towards the equator. At the same time, less dense surface water at the equator flows towards the poles along the ocean surface. The combination of this temperature/density difference, and the deflection caused by the Coriolis Effect, creates a continuous ocean water cycle (see Figure 3).

Materials

Safety Precautions

Wash hands thoroughly with soap and water before leaving the laboratory. The food dye will stain skin and clothing. Please follow all laboratory safety guidelines.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply to the disposal of laboratory waste before proceeding. All resulting solutions may be disposed of according to Flinn Suggested Disposal Method #26b.

Prelab Preparation

1. During shipment and use, the surfaces of the Coriolis Effect Model can lose their effectiveness. To increase the sensitivity, spray the topside of the white surfaces and the underside of the pink layer of the model with a simple cleaner and wipe dry. Dry erase board cleaner works well.
2. During use, if the sphere does not make a line across the surface, lift the pink layer off of the white underlayer to erase any previous markings. If this does not sensitize the pink layer enough, repeat step one.
3. Use a hook and loop fastener or sticky tack to attach the launcher to the edge of the Coriolis Effect turntable so that the open end points toward the center of the model (see Figure 4). Attach the launcher approximately 90 degrees from the point where the pink layer attaches to the turntable. Ensure the launcher can be tilted off of the turntable so the pink layer can be lifted as needed in steps one and two above.

Procedure

1. Place the metal sphere at top of the launcher and release. Do not spin the turntable for this trial. The sphere will travel across the Coriolis Effect Turntable and make a line on the pink surface. If no line is visible refer to the Prelab Preparation section. Note the path the metal sphere travels when the turntable is motionless.
2. Turn the turntable counterclockwise and launch the sphere again. Note the path the metal sphere travels when the turntable is spinning counterclockwise. This simulates a view of the Earth from the North Pole.
3. Repeat this launch with a volunteer wearing safety goggles or glasses looking eye level to the turntable. Launch the metal sphere so that it travels toward the eyes of the volunteer. Have the volunteer describe the movement of the metal sphere. Or with the previously marked curved path still on the pink layer, hold the metal sphere above the turntable and move it slowly straight across the turntable as you slowly turn the turntable with the other hand. The students should see that the sphere moved straight but the path appears curved because of the spin of the turntable.

Observations

1. Describe or draw the path of the metal sphere when the turntable is motionless.
2. Describe or draw the path of the metal sphere when the turntable is moving in a counterclockwise direction. This is similar to a view of the Earth if looking down on the North Pole.
3. Record the description of the sphere’s movement given by the volunteer in step 3.

Ocean Currents Activity

1. Remove the launcher from the turntable.
2. Place a pie or cake pan in the center of the turntable and fill with water to a depth of about ½ inch. For a more dramatic effect warm the water before adding it to the pan.
3. Place ice and water in the metal can and place the can in the center of the pie pan.
4. Use one hand to turn the turntable slowly being careful not to slosh the water. Keep the rotation at a constant rate.
5. After at least one minute, place a few drops of dye around the outside perimeter of the can where the water has been cooled by the ice bath in the can.

Observations

1. Describe or draw the path of the food dye through the water.
2. How is this path similar to the path of ocean currents?

Teacher Tips

• Motion on the surface of a sphere is complex. On Earth, the vertical axis of rotation is an imaginary line connecting the North and South Poles. The maximum vertical rotation on a sphere is at the poles and there is no vertical rotation at the equator. This is also seen on Earth—the Coriolis Effect has no effect at the equator and increases in magnitude moving from the Equator to the poles.
• Another good example of the Coriolis Effect can be seen on a merry-go-round. If person A was to sit in the middle of a spinning merry-go-round and throw a ball to person B standing outside of the merry-go-round the ball would appear to curve to person A and would appear to travel in a straight line to person B. The ball actually traveled in a straight line but, to person A, it appeared to be deflected because of their point of reference.
• Contrary to popular belief, the Coriolis Effect does not affect the way water travels or spins in toilets and sinks—they are too small to really experience the Coriolis Effect. The tap and drain designs or configurations of toilets and sinks are what really determine the way water spins within these fixtures.
• The Coriolis Effect occurs on Mars in a similar fashion as Earth. Mars rotates at about the same rate as Earth and has similar weather systems. Have students explore more about Coriolis Effects on Mars.

Answers to Questions

1. Describe or draw the path of the metal sphere when the turntable is motionless.

   The metal sphere will travel in a straight line across the turntable.

2. Describe or draw the path of the metal sphere when the turntable is moving in a counterclockwise direction. This is similar to a view of the Earth if looking down on the North Pole.

   The metal sphere moves along a curved path.

3. Record the description of the sphere’s movement given by the volunteer in step 3.

   When viewed from the side, rather from above, the sphere will appear to move in nearly a straight line, similar to the motionless turntable. Any curvature in the sphere’s path is due to friction between the sphere and the turntable.