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Unit 8.12 Exploring the Solar System
Overview of the unit
This unit builds on previous units on forces (units 6.4
and 7.11) and space (units 6.6 and 7.13). Students
will learn about the effects of gravity, and how to
differentiate between mass and weight. They then
apply what they have learned about gravity to
consider the science behind planetary orbits, satellite
technology, and manned and unmanned space
travel.
Concept strands
In completing this unit students will work towards
Learning outcomes E5 and E6.
Learning
outcome
Emerging Developing Mastered
E5 Explain
the effect of
gravity in the
solar system.
Outline the
movement
of bodies
in the solar
system.
Describe
the effect
of gravity
in our solar
system.
Explain
the effect
of gravity
in the solar
system.
E6 Compare
advantages
and disad-
vantages
of different
methods of
space explo-
ration.
Identify
ways in
which
humans
learn more
about space.
Describe
one way
in which
humans
learn more
about space.
Compare
advantages
and disad-
vantages
of different
methods
of space
exploration.
Investigating scientifically strands
The work in this unit will allow students to practice
and improve the following process skills:
Investigating
skills
Emerging Developing Mastered
S8 Construct
an
appropriate
and complete
table to recordobservations/
data.
Record
observations/
data in some
kind of
systematicway.
Record
observations/
data in a
simple
table.
Construct an
appropriate
and
complete
table torecord
observations/
data.
Equipment and resources required
newton meter, clamp stand, slotted masses, graph
paper, 1-m length of string, tennis ball, 5-cm length
of dowel, glue or sticky tape, sharp knife
Key terms
gravity – the cause of the force that pulls everyday
objects (and us!) towards the ground; really, it pulls
us towards the centre of the Earth
lenses – curved pieces of glass used to focus or
enlarge an image, for example in a magnifying glass
mass – the amount of matter in an object (every
object is made up of atoms, and each atom has
atomic mass; the mass of an object is the total of
these atomic masses)
moon – a moon is a natural satellite of a planet (in
English, we use the same word as the name of our
moon; because it’s a name, we give it a capital M –
the Moon!)
orbit – the circular or elliptical path of a planet
around the Sun, or a moon or artificial satellite
around a planet
probe – a probe is an unmanned craft, often small,
which is sent into space or to other planets, moons
or comets for scientific research; we also send probes
deep into the ocean
shuttle – a reusable spacecraft, designed to survive
a trip to space in good enough condition to be used
many times; although the shuttles themselves were
reused, they were lifted to space by a one-use rocket
Soviet Union – a country that was made up of
Russia, Ukraine and several other modern countries
the Space Race – the competition between the USA
and the Soviet Union to be the first to achieve various
goals in space exploration
telescope – a device that allows us to look at distant
objects in detail
tide – the regular change in sea level (when the sea
level is highest in a day, it is a high tide; when the
sea level is lowest, it is a low tide)
universe – everything that exists: all of the planets
and stars, and everything on them and between them
weight – the weight of an object is a measure of the
gravitational force that pulls it to another object;
this depends on the mass of both objects, and the
distance between them (the same object weighs more
(is heavier) on Earth than on the Moon)
Common misconceptions
• Weight and mass are the same.
• Gravity is proportional to the height of an
object.
• Gravity only acts on Earth.
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Introducing the big idea in the unit –
engaging the students
How do humans explore our Solar System?
Introduce by asking students if humans have
traveled to any part of the Solar System apart from
Earth. They will probably be aware of the Moon
landings from the 1960s and 1970s. This can lead to
a discussion of why there have not been any recent
missions to the Moon, and why manned missions
to the planets have not happened. Ask what other
methods have been used for space exploration –
they will probably have heard of the Hubble Space
Telescope and the International Space Station.
Explain that in this unit they will find out about some
of the problems associated with space exploration
and how scientists are pushing the boundaries.
Team, individual and class activities
Getting started
Introduce the unit by asking students what they can
recall from earlier units about the Solar System and
about human exploration of space.
What do we use satellites for in our everyday lives?
(Students should recall from Grade 6, Unit 6 that
satellites are used for communications, navigation,
weather forecasting, astronomy, etc.)
When a car travels at constant speed (The forces
acting are balanced)
When the car accelerates (The forces acting are
unbalanced)
When the car decelerates (The forces acting are
unbalanced)
1 Why does gravity keep you on the ground? (E5, S8)
Introduce the unit by asking students how they
know that gravity is a force. Expect responses such
as ‘the Earth’s gravity pulls objects and people
towards the Earth.’ Students may also recall that
this gravitational pull keeps the Moon and artificial
satellites in orbit and that the Sun’s gravitational
pull keeps the planets in orbit.
You might wish to explain that although the story
about Newton and the apple may not be true, it
illustrates an important point – that good science
often involves looking at an everyday occurrence
and asking the question ‘Why?’.
Before the apple falls, what is its speed? (Answer:
zero)
When the apple is falling is its speed still
zero? (Answer: No, its speed is changing – it is
accelerating.)
Is the force caused by a gravitational field a contact
force or a non-contact force? (Answer: non-contact
force)
Activity 1.1
Each team will need: newton meter, clamp stand,
slotted masses
This simple experiment gives students the chance
to familiarize themselves with the equipment and
also with the terminology, particularly starting to
understand the difference between force (or weight)
in newtons and mass in kilograms.
Students plot graphs of their results, and should find
that the force in newtons is approximately 10 times
the mass in kilograms.
Support: Worksheet 12.1
What is the numerical relationship between the mass
and the force that acts on it? (Answer:
mass in kilograms is equivalent to weight in
newtons × 10)
Place Gravitational
force (N/kg)
Weight of
1 kg 0.5 kg 10 kg 80 kg
Earth 10 10 N 4.9 N 98 N 800 N
Moon 1.6 1.6 N 0.8 N 16 N 128 N
Mars 3.8 3.8 N 1.9 N 38 N 304 N
Sun 274 274 N 137 N 2750 N 21920 N
Jupiter 24.9 24.9 N 12.5 N 249 N 1992 N
Can you say how people move differently on the
Moon? Can you explain it? (Students’ answers should
include the idea that the gravitational pull is smaller
on the Moon than on Earth, so astronauts were able
to take longer and higher leaps.)
What problem would there be for people visiting
Jupiter? (Answer: They would weigh 2.5 times as
much as they do on Earth, so moving around would
be difficult and tiring.)
What is the weight of 1 kg at these distances from
Earth?
Answers:
0 m 10 N
1000 km 7–8 N
10 000 km 1.5 N
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40 000 km about 0.2 N
50 000 km about 0.1 N
Worksheet 12.2 (page 172) addresses some
misconceptions about gravity by requiring students
to sort 12 statements into True or False.
2 How do satellites stay ‘up’? (E5)
This section introduces students to the science behind
satellite orbits and leads to an understanding of why
they do not fall to Earth. The graph in the previous
section has shown how the gravitational pull drops
to almost zero at a point 40 000 km above the
surface of the Earth.
Activity 2.1
Each team will need: 1-m length of string, tennis ball,
5-cm length of dowel, glue or sticky tape, sharp knife
Note: if in doubt about students’ ability to handle the
knife safely, you should make the slit in the ball.Students follow the instructions to make the model.
Their hand represents the Earth’s surface and the ball
represents the satellite. They will notice the circular
path of the satellite and that they need to spin at a
speed fast enough to keep the ball ‘in orbit’. If they
allow the speed to drop the orbit collapses.
What force pulls the satellite towards the center?
(Answer: weight or gravitational force)
What would happen if it were moving more slowly?
(Answer: the satellite would move into a lower orbit
or fall to the ground)What would happen if it were moving more quickly?
(Answer: the satellite would move to a higher orbit or
leave orbit if it reaches escape velocity)
3 The Solar System (E5)
Although students have seen diagrams of the Solar
System earlier in their study of science, this section
focuses on the relative sizes of the planets and moons
and relates these facts to our understanding of the
shapes of the orbits.
Look for the following points in students’
explanations about relative masses:• the planets and moons all orbit the Sun
• the larger planets such as Jupiter and Saturn
are still not large enough to cause the other
planets to move out of their solar orbit
• the Sun is massive enough that its gravitational
pull can keep even very distant planets (such
as Uranus and Neptune) in orbit around it.
Worksheet 12.4 sets a task of plotting a graph of the
number of moons versus planet size.
Differentiation
Extension: Worksheet 12.4a (see page 174)
Support: Worksheet 12.4b (see page 176)
4 Exploring the Solar System (E6)How do the silica glass tiles protect the shuttle and
its crew? (Answer: As silica glass is a bad conductor
of heat, the heat generated by re-entry does not pass
through the tiles to the inner wall of the shuttle.
Silica glass has a very high melting point, so can
withstand very high temperatures.)
Which of the missions were manned and which were
unmanned? (The only manned mission in the list is
Apollo 11.)
See students’ own descriptions of advantages and
disadvantages – some examples are given here:
Mission type Advantages Disadvantages
Telescopes on
Earth
relatively cheap
can be used
by amateur
astronomers
dependent on
weather (need
clear skies)
Earth’s atmosphere
absorbs some
wavelengths, e.g.
ultra violet
Telescopes in
space
not affected by
Earth’s weather and
atmosphere
expensive to
launch
difficult to
maintain
Probes to the
Moon and
planets
do not need to carry
food, water, etc. as
a manned mission
would need
difficult to
maintain and
repair
delay in
communication
between ground
and probe
Probes that
leave the
Solar System
provide information
about outer planets
and how our SolarSystem formed
long periods of
time involved
communication
is difficult – very
long delay in
communication
between ground
and probe
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Mission type Advantages Disadvantages
Manned
mission
no delay in
communication
between astronaut
and technology –
the astronaut can
respond quickly to
changing situations
expensive and
risky
modules need
to carry food,
water, breathable
atmosphere, etc.
harmful effects of
cosmic radiation
Rovers can make physical
contact and
can investigate
composition
of surface and
atmosphere
can be damaged
during landing
difficult to
maintain and
repair
delay in
communication
between ground
and rover
Observation
from Earth
relatively cheap
technology can be
upgraded
Earth’s atmosphere
absorbs some
wavelengths, e.g.
ultra violet
Differentiation
Extension: Worksheet 12.5a (page 178) compares two
different space exploration technologies. Students
cut out cards about the Hubble Telescope and a Mars
rover and place them in the correct column.
Support: Worksheet 12.5b (page 183) sets a task forstudents to design a Venus rover.
6 Presentation task
Each team will prepare a presentation about space
exploration.
Assessment
Making use of peer assessment
Using Worksheet 12.2, one student from each team
chooses a true (or false) statement and asks a team-
mate to describe the evidence that this statement
is true (or false). They swap roles until each team
member has had an opportunity to describe evidence
for one true and one false statement.
Collecting items for evidence of achievement
Completed worksheets
Success criteria for the learning outcomes
Students will be able to:
E5: Explain the effect of gravity in the solar system.
•Emerging: Outline the movement of bodiesin the solar system.
• Developing: Describe the effect of gravity in
our solar system.
• Mastered: Explain the effect of gravity in the
solar system.
E6: Compare advantages and disadvantages of
different methods of space exploration.
• Emerging: Identify ways in which humans
learn more about space.
• Developing: Describe one way in which
humans learn more about space.
• Mastered: Compare advantages and
disadvantages of different methods of space
exploration.
Encouraging self-reflection and self-assessment in
students
To summarize their learning during this unit, ask
students to create a mind map with the words Space
Exploration at the centre.
Further suggestions for additional activities
and investigations
If students have access to the internet, they could
take part in galaxy zoo:
http://www.galaxyzoo.org/#/
Links, references, URLs for the students to use
There is a huge range of online material about
gravity and space exploration. These are just a few:
http://www.space.com/science-astronomy/
This NASA website has quizzes and games:
http://mars.nasa.gov/participate/funzone/
This website enables students to calculate their
weight on other planets and the Moon:
http://www.exploratorium.edu/ronh/weight/
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