Materials Included In Kit

Additional Materials Required

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. The food dye will stain skin and clothing. Please review current Safety Data Sheets for additional safety, handling and disposal information.

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 solution may be disposed of according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are provided in this kit for 5 groups of students. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period.
• In Part II, the water for the pan may be pre-heated before adding it to the pan to create more dramatic cold water/warm water density observations.
• 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, 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 and Earth and has similar weather systems. Have students explore more about Coriolis Effects on Mars.
• 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.

Sample Data

Part I. Modeling the Coriolis Effect Observations

The chalk line was deflected in a semi-circular pattern to the right when the model was spun counterclockwise. The chalk line was deflected in a semi-circular pattern to the left when the pad was spun clockwise. The chalk line was deflected more rapidly when the pan was spun faster.

Part II. A Model for the Coriolis Effect and Ocean Currents Observations

The blue dye was deflected to the right as it left the cup and entered the warmer surrounding water. The colder blue dye initially flowed towards the bottom of the pan as it left the cup because it is more dense than the surrounding warmer water. The dye swirled as it moved toward the edge of the pan. The water outside of the cup eventually became all blue.

Answers to Questions

Part I. Modeling the Coriolis Effect Observations 

1. What does the spinning pan used in this activity represent? What does the chalk line represent?

   The spinning pan represents rotational motion of the Earth. The chalk line represents an object moving across the surface of the Earth.

2. Were the chalk lines that were drawn straight or curved?

   The chalk lines curved as they were drawn.

3. Describe the differences between the chalk lines that resulted from both the clockwise and counter-clockwise spinning of the plate. Which way was each chalk line deflected?

   The chalk line was deflected to the right when the pan was spun in a counter-clockwise direction. The chalk line was deflected to the left when the pan was spun in a clockwise direction.

4. What happened to the chalk line when the plate was spun at a faster rate of speed? What would happen to objects if the Earth were to spin at a faster speed?

   The chalk line was deflected more when the pan was spun at a faster rate of speed. If the Earth rate of rotation were faster, objects would be deflected more readily.

5. Would an airplane departing from Ft. Lauderdale, FL, to Chicago, IL, appear to be deflected to the right or to the left as it flies through the air?

   The airplane would be deflected to the right as it flew.

6. Which way would a ship travelling from Melbourne, Australia to Santiago, Chile be deflected? What about the same ship travelling back to Australia from Chile?

   In both cases the ship would be deflected to the left. The direction of travel does not matter, all objects are deflected to the right in the northern hemisphere and to the left in the southern hemisphere.

Part II. A Model for the Coriolis Effect and Ocean Currents

7. In what manner/direction did the dye move initially when it left the cup?

   The dye was deflected to the right as it left the cup.

8. What type of pattern did the blue dye eventually form toward the edge of the pan? Why did this pattern appear?

   The blue dye eventually started to swirl (formed eddies) as it left the cup. The swirling formed because of a combination of the cooler blue dye moving the warmer water outside the cup and towards the outside edge of the pan and the disruption caused by the Coriolis Effect.

9. How is the motion of the water in the pan similar to ocean currents?

   Just as was seen in the pan, the more dense cold water from 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 and along the ocean surface creating a continuous ocean water cycle.

10. Optional: Why is the force associated with the Coriolis Effect sometimes called an “imaginary” force?

    The Coriolis Effect force is an imaginary force because objects that are affected by it are really following a straight path. The apparent deflection that is seen is really only occurring because of the rotation of the Earth.

Introduction

Investigate the Coriolis Effect and how objects move over the surface of a rotating planet using hands-on activity models.

Concepts

• Coriolis effect
• Wind current
• Ocean current

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 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 toward 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).

Experiment Overview

In Part I of this activity, a model for the movement of an object across the surface of a rotating planet due to the Coriolis Effect will be explored. In Part II, the effect of temperature and the Coriolis Effect on ocean currents will be modeled.

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.

Procedure

Part I. Modeling the Coriolis Effect

1. Obtain the Coriolis Effect Model, a piece of black construction paper, scissors, tape and a piece of chalk.
2. Cut the piece of black construction paper into circle just large enough to cover the bottom of the pan (see Figure 4).
   {12828_Procedure_Figure_4_Construction paper and pan}
3. Use several pieces of clear tape to affix the black construction paper circle to the bottom of the pan.
4. Set the Coriolis Effect Model on the tabletop and have a partner begin to slowly spin the pan of the model in a counterclockwise direction. This is the direction the Earth spins when viewed from above the North Pole.
5. As the model is spinning, try to draw a straight line down the middle of the black construction paper using a piece of chalk. Stop spinning the pan and examine the chalk line. Record all observations in the data table.
6. Now have a partner begin to slowly spin the model in a clockwise direction. This is the direction the Earth spins when viewed from above the South Pole.
7. As the model is spinning, try to draw a straight line down the middle of the black construction paper using a piece of chalk. Stop spinning the pan and examine the chalk line. Record all observations in the data table.
8. Repeat steps 6 and 7 only this time spin the pan at a faster rate of speed. Record all observations in the data table.
9. Answer the Post-Lab Questions for Part I on the worksheet.

Part II. A Model for the Coriolis Effect and Ocean Currents

10. Obtain the Coriolis Effect Model from Part I, a Styrofoam^® cup half-filled with ice cubes, a clay stick and blue food dye solution.
11. Remove the piece of black construction paper and tape from the Coriolis Effect Model.
12. Use small pieces of clay to cover the four rivets on the Coriolis Effect Model Pan. This will ensure the pan will not leak when water is added (see Figure 5).
    {12828_Procedure_Figure_5_Clay over rivets}
13. Fill the pan half full with room temperature tap water.
14. Using a pushpin, poke four small holes evenly spaced along the sides of the Styrofoam cup just above the bottom of the cup (see Figure 6).
    {12828_Procedure_Figure_6_Pinholes in Styrofoam cup}
15. Place the Styrofoam cup in the center of the pan (see Figure 7).
    {12828_Procedure_Figure_7}
16. Have a partner begin to spin the pan of the Coriolis Effect Model counterclockwise. Spin the pan for 30 seconds.
17. Continue to spin the pan and, using a pipet, place 9–10 drops of food coloring into the Styrofoam cup.
18. Fill the Styrofoam cup approximately ¼ full with tap water.
19. Continue to spin the pan for an additional 30 seconds and observe the diffusion pattern of the blue dye as it exits the cup. Record all observations in the data table.
20. Answer the Post-Lab Questions for Part II on the Worksheet.

Student Worksheet PDF

12828_Student1.pdf