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Unit 6: Sound and space

GRADE 8 – Unit 6: Sound and space — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 10 parts Lesson 1 of 14 1 quiz

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Lesson summary

GRADE 8 - Unit 6: Sound and space — HIA INTERNATIONAL notes: Describe sound waves, loudness, pitch, echoes and interference, the structure of the Earth and plate tectonics, the Moon and nebulae.Source — sound is produced by vibrating objects.Medium — it travels as a wave through …

  • Best reflectors
  • Reinforcing
  • Cancelling
  • Boundaries
  • Constructive
  • Destructive

Part 1 of 8Sound waves

Source
  • Source sound is produced by vibrating objects.
Medium
  • Medium it travels as a wave through a material with particles and cannot travel through a vacuum.
    • (solid, liquid or gas)
Wave
  • Wave particles vibrate backwards and forwards in the direction the wave travels.
Speed
  • Speed about 343 m/s in air.

Part 2 of 8Loudness and pitch

PropertyDepends onUnit
LoudnessAmplitude: larger amplitude is louderDecibels
PitchFrequency: higher frequency is higher pitchHertz (Hz)
Frequency
Frequency the number of vibrations per second.
Amplitude
Amplitude the maximum distance particles move from their rest position.

Part 3 of 8Echoes

Echo
Echo a reflected sound heard after the original sound.
Best reflectors
  • Best reflectors hard, smooth, flat surfaces; soft surfaces absorb sound.
Uses
  • Uses bats find insects, ships find water depth and ultrasound images show an unborn baby.
Distance
  • Distance sound travels to the surface and back, so distance = speed × time ÷ 2.

Part 4 of 8Interference of sound

1Reinforcing
  • Reinforcing waves meeting with peaks together add their amplitudes, giving a louder sound.
2Cancelling
  • Cancelling a peak meeting a trough of equal amplitude gives zero, so no sound.
3Noise-cancelling headphones
  • Noise-cancelling headphones create a wave that cancels the sound from the surroundings.
4Condition
  • Condition complete cancelling needs equal frequency and amplitude.

Part 5 of 8Structure of the Earth and plate tectonics

Layers
  • Layers the crust is solid rock, the mantle is thick hot rock, and the core is made of iron and nickel.
    • (liquid outer, solid inner)
Plates
  • Plates the crust is broken into about a dozen large plates, moved a few centimetres a year by convection currents in the mantle.
Boundaries
  • Boundaries plates push, pull or slide past each other, and stress builds up and is released as earthquakes or volcanoes.
Constructive
  • Constructive plates move apart and new crust forms.
Destructive
  • Destructive plates collide and one is forced under the other.
Conservative
  • Conservative plates slide past each other and earthquakes occur.
Evidence
  • Evidence matching coastlines and fossils across the Atlantic;
    • the Himalayas still rise because India still pushes north.

Part 6 of 8Formation of sedimentary rock

1
Weathering breaks rock into fragments.
2
Erosion and transport by rivers move and round the fragments.
3
Sediment is deposited in layers, e.g. on the sea bed.
4
Layers above compact those below, squeezing out water.
5
Dissolved minerals cement the grains into rock.

Part 7 of 8Eclipses, the Moon and nebulae

Eclipses, the Moon and nebulae
Solar eclipse
  • Solar eclipse the Moon is between the Sun and the Earth.
Lunar eclipse
  • Lunar eclipse the Earth is between the Sun and the Moon.
Giant impact theory
  • Giant impact theory a Mars-sized planet, Theia, collided with the early Earth and the debris was pulled together by gravity to form the Moon.
Evidence
  • Moon rocks have a composition very similar to Earth’s mantle.
Nebula
Nebula a cloud of gas and dust in space from which stars and planets form.
Solar System formation
  • Solar System formation gravity pulled the cloud together, it spun faster and formed a hot centre (the Sun) and a spinning disc from which planets formed.

Part 8 of 8Earthquakes and volcanoes

Seismometers
  • Seismometers study earthquake waves, which show where boundaries between layers lie.
Volcanoes
  • Volcanoes form where plates move apart or where one plate is forced beneath another and rock melts.

Key terms

TermMeaning
EchoA reflected sound heard after the original sound.
FrequencyThe number of vibrations per second, in hertz.
CrustThe outer layer of the Earth.
MantleThe thickest layer of the Earth, between crust and core.
CoreThe centre of the Earth, made of iron and nickel.
Convection currentMovement of heated material that moves tectonic plates.
NebulaA cloud of gas and dust in space.
Plate boundaryWhere two tectonic plates meet.

Avoid these mistakes

1
Saying sound can travel through a vacuum — it needs particles.
2
Saying the Moon formed when an asteroid hit the Moon — a Mars-sized planet collided with the early Earth.
3
Saying the giant impact theory is proven — it is the theory best supported by the evidence.
4
Confusing the two eclipses — the Moon is in the middle in a solar eclipse; the Earth in a lunar eclipse.
5
Saying the plates float on the core — they are moved by convection currents in the mantle.

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