Activity # 3
PUTTING A SPIN ON THINGS
Lesson at a Glance: Students gain an understanding of the Coriolis Effect and the effect of
the Earth’s rotation on ocean circulation by attempting to draw straight lines on a rotating
sphere.
Suggested Prerequisites: Read or review pages 13 and 14 in Chapter I – The Holidays Begin.
Focus Question: Why do ocean currents move clockwise in the Northern Hemisphere and
anti-clockwise in the Southern Hemisphere?
Background:
The tropics get more sunlight than the poles because the Sun’s rays fall more directly on the
surface of the Earth at the equator. This uneven heating of the Earth results in higher
temperatures near the equator and lower temperatures near the poles. This temperature
difference causes convection (like boiling water in a pot) in the atmosphere and ocean. The
circulation of the ocean (currents) and the atmosphere (winds) between the tropics and the
poles helps to even global temperatures and make most of Earth’s surface habitable to living
organisms.
On a motionless Earth this global convection would be a simple back and forth circulation
between the equator and poles. However, because the Earth rotates, circulation in the
atmosphere and ocean is deflected from a simple north-south flow and forms rotating circular
and spiral patterns. This deflection is called the Coriolis Effect.
The Coriolis Effect only applies to things that are not tightly bound to the Earth’s surface and
that move north or south across hundreds of kilometres. This includes winds, ocean currents
and airplanes. Things moving east-west are not affected. Contrary to popular myths, the
Coriolis Effect does not influence the rotation of water in toilets and sinks.
The Coriolis Effect results from the rotation of the Earth and differences in the speed the
surface is moving at different latitudes (distance in degrees north or south of the equator).
The Earth rotates on its axis (anti-clockwise as seen from above the North Pole) once every
24 hours, so every point on the Earth’s surface makes one complete rotation (360) around the
Earth’s axis every 24 hours. This is called angular velocity and is equal to 360 every 24
hours.
North
Pole
There are 360º in a
circle. Each day (24
hours) the Earth
rotates once on its
axis through 360º.
1
In common usage, velocity and speed are treated as equal, but in scientific use they are very
different. Velocity refers to the rate of movement (distance per unit of time) in a specific
direction relative to an observer. Speed is also the rate of movement but does not depend on
direction.
The speed for any point on the Earth’s surface depends on the total distance covered in 24
hours, not the number of degrees. The circumference of the Earth is about 40,000 km at the
equator, so a point on the equator will travel 40,000 km in 24 hours during one rotation of the
Earth. This works out to a speed of 1,667 kilometres per hour (kph). (40,000 km  24 hours =
1,667 kph)
Because the Earth is a sphere, it’s circumference at 60 north and south of the equator is only
about 20,000 km and the linear velocity of rotation is around 830 kph. At the poles (90
latitude north or south) the linear velocity of rotation is 0 kph.
Imagine an airplane flying to the South Pole from the equator. The flight will take 9 hours.
The course is due south (see below) from point A (equator at 0) to point C (South Pole at
90S). The plane leaves an airport on the equator (point A) where the Earth is rotating
eastward at a linear velocity of 1667 kph. Once airborne, the airplane is no longer in contact
with the surface and is free of the Earth’s rotation, but the surface of the Earth below
continues to rotate eastward. As the plane travels south the linear velocity of the Earth’s
surface below is increasingly slower at higher latitudes. After 6 hours the plane passes over
latitude 60S (point B), where the linear velocity of the surface below is only 833 kph. The
airport (A) where it started has moved east 10,002 km (1667 kph x 6 hours) from its original
position.
rotation
A
A
A
0
0
B
B
C
90
Planned route
60

90
After 6 hours
0
B
60

C
90
60

After 9 hours
At the end of the flight after 9 hours, the airport location (A) has rotated eastward 15,000 km,
point B at latitude 60S has rotated about 2500 km east, but the destination at the South Pole
(C) has not moved. The actual flight path of the plane was due south, but the apparent path on
the surface of the Earth curves to the left (anti-clockwise) due to the Coriolis Effect. The
deflection due to the Coriolis Effect would be opposite in the Northern Hemisphere, with the
apparent path curving clockwise to the right.
Because the speed of rotation on the surface of the Earth changes with latitude, anything not
bound to the surface appears to follow a curved path as it moves north or south. The Coriolis
Effect and the resulting curvature are greater near the poles because the diameter of the circles
of latitude decrease more rapidly near the poles than near the equator. The effect is also
greater for larger changes in latitude (the greater the movement north or south the greater the
deflection). The deflection due to the Coriolis Effect is only important over large distances
2
(hundreds of kilometres) and there is no deflection for anything moving east or west because
it does not change latitude and the linear velocity remains the same.
The paths of ocean currents flowing north or south in the ocean basins are deflected in the
same way as the flight path of the airplane. This deflection (combined with the shape of the
ocean basins and global wind patterns) causes currents to curve into broad circular patterns
called gyres. Gyres dominate the flow of surface water in the major ocean basins. In the
Northern Hemisphere ocean currents are deflected to the right and gyres rotate clockwise.
Ocean currents are deflected to the left in the Southern Hemisphere and gyres rotate anticlockwise.
This circulation has dramatic consequences for global climate and the biosphere, both in the
ocean and on the land. This is explored more completely in Activity # 4 – Current Affairs.
Queensland Learning Outcomes & Levels:
Energy & Change 3.1 – Students collect data and make and test inferences to describe the
effects of forces on the motion and shape of objects.
Energy & Change 4.1 – Students design and perform investigations into relationships
between forces, motion and energy
SOSE-PS 4.4 – Students use latitude, longitude, compass and scale references to make
inferences about global patterns.
Assessment Ideas: Students successfully complete the activity sheets for parts I and III of the
Coriolis Research and Investigation.
Key Vocabulary:
axis
circumference
Coriolis Effect
current
equator
gyres
latitude
rotation
speed
Time: 2-3 class periods, depending on the students’ prior knowledge.
Materials Needed:
(for class demonstration)
 1 large mounted globe
 2 large sticky dots
(per group of students)
 1 small mounted globe (10-15 cm diameter) if available or plastic balls 20-30 cm
diameter with well defined poles (like a soccer ball).
 10 small sticky dots
 2 dry erase (white board) markers (or other easily erased medium) in different colours
 1 tape measure
 string
3
 copies of the Coriolis Research and Investigation activity sheets for Parts I & III (one
per student)
Activity:
Part I – The Rotation Mystery
1. Show the students the large globe and ask them what they know about globes and their
features. Ask them to answer the following questions on their activity sheets:

What is a globe? (A 3-dimensional model of the Earth.)

What is the axis of rotation? (The imaginary line through the Earth around which the
Earth rotates, like the axle of a wheel.)

What are the North and South Poles? (The points on the surface of the Earth
intersected by the Earth’s axis of rotation.)

What is the equator? (The circle of maximum circumference on the surface of the
Earth exactly halfway between the poles and perpendicular to the axis of rotation.)
2. Remind them that a globe is a model of the Earth. Ask them why it is a better model than
a map, a drawing or a picture (maps, drawings and pictures are flat and 2-dimensional
and distort physical features and perspectives; the globe is spherical like the real Earth
and therefore more accurate.).
3. Divide the students into groups and give each a small mounted globe or plastic ball, 10
sticky dots and an erasable marker.
4. Review and locate the basic features of a globe including the poles, the equator, continents
and oceans and lines of latitude and longitude. Focus on the lines of latitude and tell the
students that they are circles parallel to the equator that represent distances north and
south of the equator. The equator is 0, the North Pole is 90N (north) and the South Pole
is 90S (south). (If the students are using plastic balls, use the dry erase markers to mark
an equator and a north and south pole on each.)
90N
60N
North Pole
30N
0
equator
Lines of latitude are circles on the
surface of the Earth parallel to the
equator. The degrees (°) of latitude
are angles north (N) or south (S) of
the equator as measured by a line
through the latitude and the centre of
the Earth. The North and South poles
are points rather than circles at 90N
and 90S latitude.
5. Have the students measure the circumference of their globes at the equator, at the north
and south poles (it is zero at the poles), and about halfway between the equator and the
North Pole. The easiest way to do this is with string, rather than directly with the tape
measure. (Note that these circles of latitude are increasingly smaller in diameter at
greater distances north or south of the equator. The North and South Poles are points
rather than circles.)
4
6. Now ask them to find and mark the latitude where the circumference of the globe is
exactly half that of the equator. (This circle represents 60ºN or 60ºS latitude. A point on
the surface here would travel half as fast as a point on the equator.)
7. Show the students the large globe (oriented with the North Pole up) and ask them which
way the Earth rotates on its axis. Use a fixed object to represent the Sun and ask them to
think about how the Sun appears to rise and set as the Earth rotates. Remind them it is the
Earth that moves, not the Sun.
8. Demonstrate the direction of spin with the “right hand rule.” Curl the fingers of the right
hand inward with the thumb pointing straight up. The thumb points towards the North
Pole and the curl of the fingers represents the direction of the Earth’s rotation. Have the
students stand up and hold their right hands out in front of them with the thumbs pointing
up. Ask them to bend their fingers at 90 and then rotate their bodies in the direction their
fingers are pointing.
9. Place a sticky-dot on the globe at the location of London, England and rotate the globe in
the direction indicated by the right hand rule. Place the globe on the floor or a low surface
and ask the students to look down on the globe from above (view from above the North
Pole). Ask them what direction the dot is rotating (anti-clockwise).
10. Place a sticky-dot on the globe at the location of Sydney, Australia and rotate the globe in
the direction indicated by the right hand rule. Hold the globe high overhead (view from
above the South Pole). Ask them what direction the dot appears to be rotating (clockwise).
11. Discuss these observations with the students and allow them to experiment with viewing
the rotating globes from various perspectives.
Part II – Angular Velocity and Speed of Rotation
1. Remind the students that the Earth is rotating on its axis, which means that they are
moving with the surface of the Earth. Ask the students, “Do you know how fast you are
moving just sitting at your desk?”
2. Have the students place a sticky dot on the North Pole and one on the equator of each
globe. Then place several dots along a direct line between these two (about every 20-30
of latitude along a single line of longitude).
3. Have them spin the globes and observe the movement of the dots. Notice that they all
complete one circular revolution of 360 around the Earth’s axis at the same time,
regardless of their latitude. (The number of revolutions per minute is called angular
velocity.)
4. Ask them to spin the globe again.




Do all the dots travel the same distance in one revolution? (Remind them of the
measurements they made earlier.)
Which dot travels the greatest distance during one revolution? (The one at the
equator.)
Which one does not move any distance at all? (The one at the North Pole.)
Are all the dots moving at the same speed? Why or why not? (Those at lower latitudes
travel faster because they move more distance in the same period of time.)
5. Provide the students with the following information:

The circumference of the Earth at the equator is 40,000 km.
5


The circumference of the Earth at latitude 60N is 20,000 km.
The circumference of the Earth at 90 (the North Pole) is zero.
6. Ask the students how long it takes for the Earth to complete one rotation. (24 hours) Ask
them to calculate the following:



How fast would they be moving at the equator?
(40,000 km  24 hours = 1667 kph)
At 60N latitude?
(20,000 km  24 hours = 833 kph)
At the North Pole?
(0 km  24 hours = 0 kph)
7. Discuss these results with the students. How does surface speed change with latitude on
the surface of the Earth? (Speed is highest at the equator, lower at higher latitudes and
zero at the poles.) Note that a person sitting at the equator is travelling with the Earth’s
rotation at 1667 kph. A person at 60N latitude is only travelling 833 kph (still pretty
fast!) and a person at the North Pole has no speed (they just turn in place).
Part 3 – The Coriolis Effect
1. Show students an illustration of major currents in the ocean. Discuss the fact that the
currents are forming more or less circular patterns called gyres. Ask the students which
way the gyres appear to rotate. (Clockwise in the Northern Hemisphere and anti-clockwise
in the Southern Hemisphere). Can they explain why?
2. Ask the students if they have ever heard of the Coriolis Effect. Can anyone describe it and
give examples? (Ask if they have ever heard that drains and toilets swirl in opposite
directions in the two hemispheres. It is often given as an example of the Coriolis Effect but
it is not true. The Coriolis Effect is very weak and only affects large things that are not
tightly bound to surface of the Earth.)
3. Ask them to imagine that they are airplane pilots. They want to fly from Borneo to the
North Pole. Have them find Borneo on their globes. (Use the big globe if they have
unmarked balls.)
4. Ask them what direction they need to fly to get from Borneo to the North Pole (due
north). Have them use a dry erase marker to draw a line on their globes from Borneo to
the North Pole. (If they have a mounted globe there should be an armature that connects
the supports at the poles of the globe. This can be used as a guide for the marker. Have
one student hold the globe steady and another draw the line. If using an unmounted globe
or ball, ask the students to try and hold the ball and the marker as steady as possible.
Hold a ruler beside the ball to act as a vertical reference line and move the marker at a
constant speed along this line.)
5. Remind the students that the Earth is spinning. Have them draw the line again, but this
time have one student turn the globe slowly and steadily while the other two are drawing.
(Remember the right hand rule!)
6. Compare the two lines and discuss the results.
 How are they different? (The first line is straight. The second line should curve to the
right or clockwise. You can see this more easily by looking down on the globe from
above.)
 Where is the line curved the least? (near the equator)
6

Where is it curved the most? (near the pole)
7. Tell them they now want to fly back to Borneo.
 What direction do they need to go? (south)
 If they fly straight south, will they end up in Borneo? (no)
 Why not? (The Earth is rotating under them.)
 Which direction do they need to fly to reach Borneo? (This gets tricky. Somewhat to
the east of a line due south to Borneo. As they fly south Borneo will be moving to the
east, so they must travel southeast. The exact direction would depend on how fast they
were flying. The slower they flew, the further east Borneo would move.)
8. Repeat Steps 5-7 for the Southern Hemisphere and have the students report their results.
(The lines will curve to the left or anti-clockwise.)
9. Ask the students to draw a line due south from the North Pole to the South Pole while the
globe is rotating. What is the result? (The line will curve clockwise in the Northern
Hemisphere and anti-clockwise in the Southern Hemisphere.)
10. Discuss these results and ask the students to explain why the lines curve. Why do they
curve in opposite directions in the Northern and Southern Hemispheres? (A point on the
surface of the Earth at the equator moves faster than a point closer to the poles. Therefore
anything not held to the surface by friction that moves north or south from the equator
will appear to follow a curved path.)
[The line is more curved near the poles because the circumference of the circles of
latitude decrease more rapidly as you approach the poles, the Coriolis Effect is greater.
Surface speed decreases by half between the equator and 60 latitude (2/3 of the distance
to the poles) and from half to zero over the next 1/3 of the distance. The greater the
distance an object moves north or south the greater the deflection.]
11. Allow the students some time to experiment with the globes and the Coriolis Effect,
drawing different routes that are northeast, southeast, etc. or cross from one hemisphere to
the other and back.
Note:
An easy and inexpensive way to do the preceding activity is with round punching balloons.
These are available in the toy or party section of many discount stores. Give each group of
students an inflated punching balloon, a globe, and a marking pen. (Remove the rubber
bands from the balloons before handing them out or the kids will be bouncing them
everywhere!) Ask them to create their own globes by drawing the equator and prime
meridian on the balloon and outlining the major continents. They can then draw the lines on
their balloon globes. After they have completed the Coriolis exercise, you can deflate the
balloons and challenge them to turn their globes into flat maps. This leads nicely into an
exploration of maps, their uses and their inherent limitations.
Discussion Questions:
1. How would the Earth be different if it did not rotate and there was no Coriolis Effect?

The most important thing is that days and nights would be 6 months long.
Demonstrate this by having a student stand in as the Sun. Have another student
holding a globe circle around the Sun keeping the Earth in the same orientation.
7

The Earth would be very hot on the day side and very cold on the night side.
Circulation of the ocean and atmosphere might be more east-west between the day
and night sides than north-south between the tropics and poles.

With no Coriolis Effect, ocean currents would not follow circular or spiral paths and
might be very irregular.
2. What would the Coriolis Effect be if the Earth rotated backwards (clockwise)? (It would
be reversed. Ocean gyres would rotate anti-clockwise in the Northern Hemisphere and
clockwise in the Southern Hemisphere. Also the Sun and Moon would rise in the west and
set in the east.)
Note:
The concept of the Coriolis Effect is quite a lot to absorb, but important for understanding
many physical processes that dominate the atmosphere and hydrosphere (all of the water on
Earth). Take it slowly. Allow considerable time for exploring the motion of the Earth.
8
CORIOLIS RESEARCH AND INVESTIGATION
Part I – The Rotation Mystery
1. What is a globe?
___________________________________________________
2. What is the axis of rotation?
___________________________________________________
___________________________________________________
3. What are the North and South Poles?
___________________________________________________
___________________________________________________
4. What is the equator?
___________________________________________________
___________________________________________________
5. Why is a globe a better model of the Earth than a map, diagram or picture?
___________________________________________________
___________________________________________________
6. Does the Earth rotate on its axis clockwise or anti-clockwise?
________________________
7. Viewed from above the North Pole, what direction do points on the surface
of the Earth appear to rotate in the Northern Hemisphere?
________________________
8. Viewed from below the South Pole, what direction do points on the surface of
the Earth appear to rotate in the Southern Hemisphere?
________________________
9
CORIOLIS RESEARCH AND INVESTIGATION
Part III – The Coriolis Effect
1. What happened when you drew a line due north from the equator to the
North Pole while the globe was rotating?
___________________________________________________
___________________________________________________
___________________________________________________
2. What happened when you drew the line from the North Pole back to the
equator?
___________________________________________________
___________________________________________________
3. What happened when you drew lines between the equator and the South
Pole?
___________________________________________________
___________________________________________________
4. What happened when you drew a line from the North Pole to the South Pole?
___________________________________________________
___________________________________________________
5. Which way do ocean gyres rotate in the Northern Hemisphere?
_________________
In the Southern Hemisphere? ______________________
6. Briefly explain the Coriolis Effect. What causes it? How does it affect
ocean currents in the Northern and Southern Hemispheres?
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
10