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Unit 6 Earth physics

Unit 6 Earth physics
By Violet Voon
 Vibrations (move back and forth) make sound
 If you hit a drum with greater force, it vibrates more and
produces louder sound.
 Our vocal cord vibrates and produces sound when we speak.
Loudness and Pitch
• Not all sounds are the same
• The bigger the vibrations (amplitude), the louder the sound
• The faster the vibrations (frequency), the higher the pitch of
the sound.
• Thunders can be loud but low pitch
• A baby crying is high pitch
• Tighten the string of a guitar produces higher pitch
• Sound at certain pitch can cause damaging vibrations even the
sound is not too loud. Glass can be broken by vibrations from
Louder sound has a bigger amplitude.
Higher pitch has a higher frequency.
Sound wave
• When a loud speaker makes a sound, its cone vibrates back and forth.
• The air molecules next to the cone move back and forth with the same
• They then push the molecules on the next layer so that they also start
• These molecules push on the next ones and so on. The molecules only
move side to side, but the vibration travels outwards . This is called sound
• Sound waves transfer sound energy.
How sound travels
Speed of sound, m/s
Steel, iron
• Sound can travel through
medium (solid, liquid or
• Sound travels the fastest
through solid, then liquid,
and slowest in gas.
• Sound cannot travel through
a vacuum, as there is no
particles to vibrate to make
a sound wave.
• The sound of the bell
becomes softer and finally
cannot be heard when the
air in the bell jar is pumped
Reflection of sound
• A sound wave will be reflected when it strikes an obstacle.
The reflected sound is called echo.
• Sound waves reflect best from large, smooth and flat surface.
• Surfaces such as glass, tiles, flat metal and smooth concrete
give good reflection of sound.
Useful echoes
• The use of echo sounding equipment has enabled humans to measure the
depth of sea , the presence and distance of an iceberg and the distance of
an enemy’s submarine.
• Echoes help the bat to work out where the insect is.
• Echoes can be used to make images from inside the body. Sound sent into
mother’s body echo back out of her body. This is to make the image of
unborn baby.
• The distance travelled by the sound is double the distance from the object
making sound to the reflecting surface.
Unwanted echoes
• Sometimes echoes are unwanted for example when recording
• In theatre the audience needs to hear the voices of people on
the stage. If there were echoes, the voices would not be clear.
• Theatres usually have no large flat surfaces to stop echoes.
Ways to reduce echoes
1. Hang Soft Curtains.
2. Add Fluffy Rugs or Carpeting.
3. Add Sound-Absorbing Plants.
4. ring in Some Cushions and Blankets.
The shapes on the walls are made to
stop echoes
The structure and age of the earth
•The earth is about 4500 million
years old
•The earth has a crust of solid rock.
•Beneath the crust is the mantle,
which is molten rock that can flow.
•In the centre is the core. It is
made of nickel and iron. The outer
core is molten, while the inner
core is solid.
•The rock found in the crust
contain metals and non-metals.
•Oxygen is the most abundant
element in the earth crust.
•The most abundant metal in the
earth crust is aluminium
Millions years ago, all the land was a large continent. Over millions of years, the land
broke up and drifted apart. This idea is called continent drift, by Alfred Wegner a
German scientist in 1912. His evidence for this idea was that:
1. The shape of the continents fit together
2. The types of rocks on the different continents match up where they fit together
3. The fossils on the different continents match up when they fit together.
But he could not explain how the drift happened, so not everyone believed his ideas.
In the 1960s, tectonic plate theory was developed. The earth’s surface is made
up of large plates. Some of the plates are under oceans, they are called oceanic
plates. Some of the plates form the continents, they are called continental
plates. The plates move slowly on the molten magma underneath them. The
plates only move about 4 cm each year.
The earthquakes and volcanoes are usually occur at the plate boundaries, the
places where tectonic plates meet.
Geological change
• Geological change happens most frequently at plate boundaries
because the tectonic plates are always moving.
• Some geological change is very slow, takes millions of years. Some
are very sudden and violent.
• The picture below shows there are many geological changes and
events such as volcanic eruptions and earthquakes t the plate
boundaries around the edge of the Pacific Ocean. The area is called
Ring of Fire.
Movement of plates
Plates moving together
• One plate may slide
underneath the other
one. This is called
• The rocks in the crust
melt as they move into
the mantle. They
become part of the
Movement of plates
Plates moving apart
• As tectonic plates drift
away from each other,
they break and crack
when they become too
• Lava erupts from the
mantle and harden to
form new crust with
new rocks. This causes
a volcano.
Movement of plates
Plates sliding past
• There is a lot of friction
between the plates as the
plates are large and
• There is always force on
the tectonic plates, so the
pressure builds up and
eventually the pressure
causes violent movement.
This is an earthquake.
Fold mountains
• Sometimes when tectonic plates move together, the rocks
crumple and fold upwards, this produces fold mountains.
• This can happen under the ocean or on land.
• The newest fold mountains are between 10 and 25 million
years old. Examples : the Himalayas in Asia and the Rocky
Mountains in North America.
• The oldest fold mountains are more than 200 million years
old. Example the Ural Mountains in Russia
The Himalayas
Rocky Mountains
Ural Mountains
• Volcanoes are usually formed at the plate boundaries when magma
from the mantle rises up through cracks in the Earth crust.
• At the Earth’s surface, magma erupts to form lava flows and ash
• Magma is the liquid rock when it is underground, lava is the liquid
rock when it is on the surface.
• The lava and ash harden as they cool to form new rocks. So each
time the volcano erupts, it gets bigger.
• Sometimes if the magma is really thick and contains dissolved gas,
pressure builds up and the eruption is violent. Gases and rock
shoot up through the opening. Violent eruptions can even cause
avalanches and earthquakes. Tsunamis also may happen if the
volcano is close to sea.
• Active volcanoes may erupt anytime; inactive or dormant
volcanoes have not erupted for a very long time. Extinct volcanoes
will not erupt again.
• Some earthquakes are extremely violent and cause a lot of
damage. Some are so light that they only register on scientific
• The size or magnitude of the earthquake depend on
1. The size of the faults (cracks) at the plate boundaries
2. How far the rocks move when the earthquake happens. In
the largest earthquakes, the rocks can move tens of metres
in seconds.
How a shadow formed?
• Light travels in straight lines called rays.
• Light rays cannot pass through an opaque
object, it blocks the light from reaching the
place behind it, thus a shadow formed.
Solar eclipse
• A solar eclipse happens when the Moon comes between the Sun and the
•The Moon blocks the sunlight.
•The shadow of the Moon forms on Earth.
•People in the middle of the shadow (umbra) observe a total solar eclipse.
•Away from the middle of the shadow of the Moon, some light rays from
the Sun can reach the Earth (penumbra), there is partial solar eclipse.
Never look at the Sun directly even
when there is an eclipse, it can
cause eyes damage
•A lunar eclipse happens when the Earth comes between the Sun and the
•The Earth blocks the sunlight.
•The shadow of the Earth is formed on the Moon.
• It does not happen every month.
•The Moon takes 27 days to orbit the Earth but the orbit of the Moon is
tilted slightly. It is not exactly the same plane as the orbit of the Earth
around the Sun.
•It happens only when the Sun, Earth and Moon are in the same straight
line .