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GRADE 5
Name:
The Earth moves in two different ways: It rotates and it revolves.
Rotation:
Rotate means to spin. This is what Earth does – it
spins like a spinning top.
A spinning top has a point on which it spins. If
you draw an invisible line through the centre
of the top through to the point, this is called
the axis. The top spins around this axis.
An axis is an imaginary line that cuts
through the centre of an object. With
planets, the axis is the imaginary line
around which the planet spins.
In the picture above, the spinning top is tilted, so its axis is tilted. Earth’s axis is also
tilted. This means that Earth spins like it is “leaning over”. The difference between the
spinning top and the Earth, is that the angle changes when the spinning top spins,
but the angle of the Earth’s axis never changes.
In the diagram, the tilt of the axis is measured as an angle from a straight line that
goes through the centre of the planet.
The angle that Earth’s axis is
tilted at is 23,5°. This angle
never changes.
Earth Axis
Sun’s rays
Arctic Circle
Tropic of Cancer
Equator
Tropic of Capricorn
Antarctic Circle
The ‘spinning around an axis’
motion is called rotation. So
we say that the Earth “rotates
around its axis.”
Earth rotates in a west-toeast direction and it takes
24 hours for it to rotate
once. The Earth rotates once
in a day. How long is one
day? In 24 hours, we have hours of sunlight and hours of darkness. This is because there
are hours when our part of the Earth is facing the Sun (day) and there are hours
where our part of the Earth is facing away from the Sun (night).
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Grade 5 Term 4 Natural Science and Technology: Planet Earth and Beyond and Systems and Control: Planet Earth: The Earth Moves
The Earth moves
GRADE 5
Revolution
To revolve also means to “turn” but we use it to describe the movement of an object
around a fixed point. For example, a “revolving door” turns around the centre point
which is fixed into the ground.
When we talk about Earth, we talk about it revolving around the Sun.
The Sun is the centre point and the Earth (and all of the planets) move around the
Sun.
Note from this diagram, that all the planets have their own pathway around the Sun.
The pathway around the Sun is called an orbit (noun). Earth travels along its pathway
continually.
The word ‘orbit’ can also be used to describe its moving around the Sun. The Earth
orbits (verb) the Sun.
© e-classroom 2014 www.e-classroom.co.za
Grade 5 Term 4 Natural Science and Technology: Planet Earth and Beyond and Systems and Control: Planet Earth: The Earth Moves
Rotation gives us DAY and NIGHT
The Earth travels around the Sun once a year.
This seems like a long time, but Earth, even though it’s travelling very fast, is very far
from the Sun, so it has a long distance to travel.
The Earth revolves around the Sun in an anti-clockwise direction.
DID YOU KNOW?
Did you know? The Earth revolves around the Sun at a speed of about
108 000 km/hr. That means that in one second, it travels 30km! If you
were to travel from Johannesburg to Durban at that speed, it would
only take you 16 seconds!
Seasons in the Northern Hemisphere
(e.g. if you lived in United States of America)
Tipped
Axis
SPRING
Earth’s
orbit
North Pole
South
Pole
Equator
WINTER
SUMMER
AUTUMN
Revolving around the Sun means that the Earth can experience seasons. Different
parts of the Earth experiences Summer and Winter, Autumn and Spring at different
times of the year – this is all because the Earth revolves around the Sun.
© e-classroom 2014 www.e-classroom.co.za
GRADE 5
Grade 5 Term 4 Natural Science and Technology: Planet Earth and Beyond and Systems and Control: Planet Earth: The Earth Moves
The Earth takes approximately 365 days to travel once around the Sun. How many
days are there in a year? ........................................
GRADE 5
The Earth rotates on its axis once every 24 hours. The axis is tilted at
23,5°. Rotation gives us day and night.
The Earth revolves around the Sun, once every 365 days. It revolves in
an anti-clockwise direction. Revolution gives us seasons.
Keywords:
Orbit (v), orbit (n), revolution, rotation, axis, tilt of the axis, day and night, anticlockwise, seasons.
Activity: Demonstrate Rotation and Revolution of the Earth
You will need:
A polystyrene ball, a skewer stick, a lamp or light without a lampshade on it.
Read and follow these instructions very carefully.
1) Push the skewer stick through the centre of the polystyrene ball – be careful not to hurt yourself!
2) The polystyrene ball is the Earth and the skewer stick is the axis. Tilt the skewer stick to the right slightly to show how the axis of the Earth is tilted.
3) Turn on the lamp and hold the polystyrene ball near the light. Can you see how the part of the ball facing the Sun is lit up, but the part not facing the light is in darkness? The part facing the light is experiencing day and the part not facing the light is experiencing night.
4) Keep the ball in one spot and rotate it around its axis. Can you see that the parts facing the Sun change? This is how we experience day and night in 24 hours.
5) Now, this one is going to take some co-ordination! Keep the axis tilted, rotate the ball around its axis and now move it in a circle around the light. Do this slowly – don’t rush it!
6) Have a look at a few things:
See that the tilt of the axis doesn’t change.
Look at the parts of the ball facing the Sun.
Look at which parts are closest to the Sun as the Earth moves around the Sun.
© e-classroom 2014 www.e-classroom.co.za
Grade 5 Term 4 Natural Science and Technology: Planet Earth and Beyond and Systems and Control: Planet Earth: The Earth Moves
KEY POINTS