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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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