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6.2 Reflections of sound What Is Reflection of Sound

 Reflection of sound:
Objectives
The bouncing back of the sound wave on
• 7Ps.02 Explain echoes in terms of the reflection of striking a surface such as a wall, metal sheet,
sound waves. plywood, etc.
• •7TWSm.02 Use symbols and formulae to Or
represent scientific ideas
when sound travels in a given medium it
strikes the surface of another medium so that
it returns in some other direction

Reflections NOTES
• One property of all sound waves is that they can be
reflected from surfaces • Sound waves reflect best from large,
smooth, flat surfaces.
• Reflection is like bouncing a ball off a wall. When a
wave is reflected, the wave behaves like the ball.
• Surfaces such as glass, tiles, flat metal
• The only difference and smooth concrete give good
is that a wave is not affected by gravity.
reflections of sound

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 Echo:
Echo is the repetition of a sound caused by
the reflection of sound waves.
• Echo arrives at the listener with a delay after the
direct sound. If this gap between the object is greater
than 1 second, the reflection is called an echo.

NOTES Useful echoes

• When you clap your hands, you hear a strange effect • Bats use echoes to find insects for food. The bat makes a sound.
on the sound.
An effect on a sound means the sound is changed. The • The sound wave reflects off the insect – there is an echo.
sound of the clap seems to last longer than usual, then
• The bat can work out where the insect is from:
fade away
1- The time taken for the echo to reach the bat.

• Clapping your hands makes a sound wave. The sound 2- The direction the echo comes from.
wave will travel away from your hands in all
directions. When the sound wave hits a wall, it is
reflected back.
The reflection of a sound wave is called an echo

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Boats can use echoes to find the depth of

water under the boat Notice that
• The distance travelled by the sound is double the distance from
1. A sound is sent from the bottom of the boat. the object making the sound to the reflecting surface.
2. The sound travels through the water and reflects off the solid
ground. • The sound has to travel from the object to the reflecting surface
3. The echo comes back to the boat. and back again.
4. The time taken for the echo to come back can be used to work
out the depth
You can see this in the picture of the bat and insect,
and in the picture of the boat.

Echoes can also be used to make images from inside the

body. Sounds sent into the mother’s body echo back out of
Unwanted echoes
her body. • Sometimes echoes are unwanted.
• For example,
This method is used to make the image of the unborn baby when recording music, echoes change the sound. A
musical note that is played once will repeat with an echo.
This effect will spoil the recording.
• A room with large flat walls would give many echoes

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Theatres usually have no large flat surfaces that Learner’s book P.205
could cause echoes

Learner’s book P.206 Learner’s book P.206

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Learner’s book P.206 Learner’s book P.206

Answers P.205- 206-207 Earth

The Earth is unlike every other
planet in the Solar System in a
number of different ways.

It is the only planet that has

liquid water on its surface.

By using a variety of advanced

techniques, scientists have been
able to discover what lies beneath
the surface of our planet.

Earth is about 4500 million years

old.

Earth is about 4500 million years

old.

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Layers of the Earth

1- The crust (solid rock).

2- The mantle, Under the crust

(which is molten (hot liquid) rock that can flow.

3- The core, In the centre of the Earth .

(It is made of the metals nickel and iron).

 The outer part of the core is molten.

 The inner part of the core is solid

The Crust Earth is Fragile

These tectonic plates float on a
rocky mantle – the layer between
The crust is the top layer that we the surface of the Earth, its crust,
live and its hot liquid core.
Thison. The crustthe
is because looks
crustdifferent
is not
in different
one places, some
continuous areas
The crust is the piece, it is
outer layer made
of the The inside of the Earth is active
have
up ofmountains,
pieces oceans, lakes
Earth that isthat
made overlap
of solid to rock
cover and therefore earthquakes and
and hills, others
the entire planet.don’t. volcanoes can be caused by these
The rocks found in the crust tectonic plates moving.
The
Theseway the crust
pieces areandis puttectonic
called together
contain metals non-metals.
isplates.
the reason that we have all of
these different formations. Over a long period of time the
movement of these plates
also forms mountains.

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The Mantle The Outer Core

The outer core is about 30% of
the Earth's mass. Its temperature
ranges from 4440°C to 6100°C
(which is as hot as the Sun!)

The outer core is a molten (super-

heated liquid) made of iron and
nickel.

Without the outer core, life on

Earth would be very different.
Scientists believe that it is the
convection of liquid metals in the
Its temperature
The (upper
mantle is theranges
and lower
layer from
within500
together)
thedegrees
Earthaccounts
Celsius for
between (500°C)
the60%
coreat
ofand
thethe
crust
outer core that create the Earth’s
Earth's
to 4,000°C
crust mass,
that isnear
making
made thefrom
outer
it molten
thecore.
thickest
rock layer of the Earth. magnetic field.

The Inner Core Learner’s book P.212

The inner core is made up of the
same metals as the outer core
(iron and nickel) but, instead of
being liquid, it is a solid.

The inner core reaches

temperatures of up to 5,500°C.

With its immense heat energy,

the inner core is like the engine
room of the Earth.

It is basically a solid ball with a

radius of about 760 miles (about
70% of the size of the Moon).

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• In 1912, a German scientist called Alfred Wegener suggested that,

Answers P.212 millions of years ago, all the land was one large continent. Over
millions of years the land broke up and drifted apart. This idea is
called continental drift.

Define:
Continental drift:
Slow movement of the continents

His evidence for this idea was that: • Wegener could not explain how continental drift
• the shapes of the continents fit together happened, so not everyone believed his ideas.\
• the types of rock on the different continents match up
where they fit together Q: Some people did not believe Wegener’s idea because
• the fossils on the different continents match up where he could not explain how continental drift happened.
they fit together What theory was developed in the 1960s that
explained this idea?
Answer: The theory of tectonic plates

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Notes \
 We now know that the Earth’s crust is made up of large tectonic
plates.
• Some of the plates are under the oceans: they are called oceanic
plates.
• Some of the plates form the continents: they are called
continental plates.

 These tectonic plates move slowly on the liquid rock called

magma beneath them.
This is how continental drift occurs.

 The plates only move about 4 cm each year, which is about

same speed as your fingernails grow

Learner’s book P.215 Answers P.215

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Answers of activity

Learner’s book P.216 Answers P.216

Similarities Differences
• a volcano is sometimes a type of • mountains are not active or do
mountain, both are made from not erupt,
rock
• both are higher than • volcanoes have lava/magma,
surrounding ground level
• both have a base and a highest • volcanoes have a crater or
point. openings.

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 Plate boundaries:
The places where tectonic plates meet (side by side).  Geological change:
happens most frequently at plate boundaries. (Explain)?

• This is because the tectonic plates are always moving.

• Some of the geological change is very slow – it
happens over millions of years.
• But some of the geological change is very sudden and
violent. such as: volcanic eruptions and earthquakes

plate boundaries around the edge of the Pacific Ocean

Movement of plates Movement of plates

The movement of tectonic plates creates three types of plate boundaries. The movement of tectonic plates creates three types of plate boundaries.

• Subduction: one tectonic plate moving • Volcano: openings in the Earth’s crust
under another tectonic plate at a plate where lava ash and gas come out onto
boundary. the Earth's surface.

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Movement of plates
The movement of tectonic plates creates three types of plate boundaries.  Fold mountains: produced when tectonic
plates move together, the rocks crumple and fold
upwards.

• This can happen

under the ocean or
on land.

• Earthquake: sudden movement in the Earth’s

crust &upper mantle caused by the build-up
pressure between two tectonic plates .

Fold mountains:
• The newest fold mountains are between 10 and 25 million years old. Watch this video about about reasons
• These include the Himalayas in Asia and the Rocky Mountains in North
America.
for volcanic formation and eruption
• The oldest fold mountains are more than 200 million years old. These Geography Lesson: What is a Volcano?
include the Ural Mountains in Russia.
| Twig – YouTube

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• Sometimes, if the magma is really thick,

How Are Volcanoes Formed? and contains dissolved gas, pressure builds
up and the eruption is violent.
Volcanoes are usually formed at the plate boundaries when magma from • Gases and rock shoot up through the
the mantle rises up through cracks in the Earth’s crust.. opening.
• Violent eruptions can even cause
• At the Earth’s surface, avalanches and earthquakes – and
magma erupts to form lava tsunamis if the volcano is close to the sea.
flows and ash deposits.

• The lava and ash

harden as they
cool to form new
rocks

Magma is the name for liquid rock

when it is underground.
Lava is the name for liquid rock when
it is on the surface.

The Three Stages of Volcanoes How Can You Move Your Plates?
Scientists have placed volcanoes in to three different categories. Earthquakes

Active Dormant (inactive) Extinct Can you remember the different ways plates can move?
An active volcano is A dormant volcano is An extinct volcano is
one that has erupted one that has not one which has erupted
recently, and there is erupted for a long thousands of years
the possibility that it time, however, it may ago, but it will away from
rubbing together towards each other
may erupt again. still erupt in probably never each other
the future. erupt again.

which kind of movement causes earthquakes?.

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some earthquakes are extremely violent and

cause a lot of damage.
Magnitude:
Some are so slight that they only register on the size of something, a number
scientific instruments.
which allows comparisons to be
The size or magnitude of the earthquake made between the strengths of
depends on the size of the faults at the plate
boundaries, and how far the rocks move when earthquakes.
the earthquake happens.

In the largest earthquakes, the rocks can move

tens of metres in seconds

Staying Safe in an Earthquake Learner’s book P.220

No one can predict when an earthquake will occur.
Design a safety plan with your family to help you be prepared.

Building a Safety Kit:

Include the following items:

• plenty of water
• flashlights
• emergency whistles
• extra shoes and clothes
• first aid kit
• battery operated radio

What else could you include

in a safety kit?

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Learner’s book P.220 Answers P.220

Did You Know…? Notes

An ‘eclipse’ occurs when one object From Earth, there are two  Opaque: description of an object that does not allow
in space blocks an observer from main types: solar eclipses light to pass through; the opposite of transparent
seeing another object in space. and lunar eclipses.

Unlike solar eclipses, lunar eclipses

 shadow: area where light has been blocked by an
can be viewed without any special opaque
equipment and without any danger
to your eyes.
 Object rays: the straight lines that show the direction of
Because the Moon reflects the Sun’s light
light, a lunar eclipse will never be
brighter than a full moon.
 Solar: description of something to do with the Sun

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Explain: The shadow looks dark ?

because the light from the Sun has been blocked from
reaching the ground. The aeroplane is made from metal
which is opaque.

The grass around the shadow looks brighter because light from the Sun is
reaching those areas

Notes What Is a Solar Eclipse?

Solar: description of something to do with the  A solar eclipse happens when the Moon comes
Sun
between the Sun and the Earth.
Eclipse: shadow caused by the Moon or
caused by the Earth

Total: description of a solar eclipse where the

Moon completely blocks the light from the Sun

Partial: description of a solar eclipse where the

Moon only partly blocks the light from the S

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What Is a Solar Eclipse? The outer edge

of the sun can be
seen in greater
detail than usual
• The Moon is made from rock, so when an eclipse
is an opaque object. occurs.

• The Moon blocks the rays of

light coming from the Sun.

• The shadow of the Moon forms

on the Earth

Photo courtesy of maaco (@flickr.com) - granted under creative commons licence – attribution

Photo courtesy of NASA Goddard Photo and Video (@flickr.com) - granted under creative commons licence – attribution

Why Do Solar Eclipses Happen? Can You Look at a Solar Eclipse?

When we look up from Earth,

the moon appears about the
same size as the sun.

During a solar eclipse, the

moon comes between the Earth
and the sun. The moon blocks
out the light of the sun.

A solar eclipse can last for as

long as seven minutes or as
little as thirty-one seconds. It can damage your eyes if you look directly at a solar eclipse.

Protect your eyes with special glasses made for solar eclipse viewing
Photo courtesy of NASA Goddard Photo and Video (@flickr.com) - granted under creative commons licence – attribution
or view an eclipse using a pinhole projector.

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What Is a Solar Eclipse?

A total eclipse is
when the sun’s
light is completely
obscured or blocked
out by the moon.

When only a part

of the sun is
blocked, it is called
a partial eclipse.
This happens two
to five times a
year.

The last total solar

eclipse to be seen in
the United States
occurred on August
21, 2017.

What Is a Lunar Eclipse? Parts of the Eclipse

A lunar eclipse happens when the Earth passes between the Moon and the The Earth casts two different shadows as it blocks the Sun’s light.
Sun and the Earth's shadow completely or partially obscures the moon.

Penumbra

Umbra

They only happen at night, during There are, on average, three

a full moon and when the Earth, lunar eclipses a year but not
Sun and Moon are aligned. all of them are total eclipses. Watch this video to see how it happens.

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The diagram below shows how the shadow of the

The picture shows a series of three
Earth forms on the Moon photographs of the
shadow of the Earth passing across the Moon.

Are There Different Stages of the Total Lunar Eclipse

Types of Lunar Eclipse?
There are three types of lunar eclipse.

1 Total Lunar Eclipse

This is when the Moon passes completely into
the umbra, or total shadow, of the Earth.

If the Moon is It’s because of the Earth’s

completely in atmosphere. The Sun’s rays
the Earth’s pass through the ring of
shadow, why atmosphere around the Earth
does it look red and are filtered. It is mostly
and not dark? i red light that passes through
and is refracted onto the
Moon’s surface, making it
appear red. Some people call
this a ‘Blood Moon’.

“Lunar Eclipse August 2007” by [Chris Baird] is licensed under CC BY 2.0

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Are There Different Did You Know…?

Types of Lunar Eclipse? You might think that solar and
The Moon takes 27 days to
orbit the Earth, but the
lunar eclipses should happen orbit of the Moon is tilted
every month.. slightly..
2 Partial Lunar Eclipse
It is only when the Sun,
This is when the Moon does not fully move into the umbra. The orbit of the Moon is not exactly Earth and Moon are in the
in the same plane as the orbit of same straight line
the Earth around the Sun. that eclipses can happen

i
The Earth’s shadow
covering a small
amount of the Moon.

“PARTIAL LUNAR ECLIPSE” by [tonynetone] is licensed under CC BY 2.0

Compare Solar eclipse to Lunar eclipse: Learner’s book P.226

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Learner’s book P.226 Answers P.226

Answers of Workbook p. 123 – 124

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