8Lc4 Travelling sound 2Sound travels through different materials at different speeds. This is because materials vary in density. Sound travels very quickly through dense materials because the vibrations are passed along quickly as the particles are in close contact. Sound does not travel through air very well because gases have particles which are far apart and they need to touch to pass on the vibrations.

Material Speed of sound in m/s

steel 6000

aluminium 5100

iron 5000

concrete 5000

glass 4500

copper 3700

brick 3000

salt water 1560

water 1500

mercury 1450

ethanol 1200

air  330

oxygen  316

carbon dioxide  260

1 Plot a bar chart to show the speed of sound in these materials.2 a Which two materials are the most dense?

b Which two materials are the least dense?c Which material allows sound to travel 4 times faster than in water?d Sound travels though cork half as fast again as it does through air. What is the

speed of sound through cork?3 Michael is sitting in a boat with a metal hull. He is hammering the bottom of the boat.

a Who will hear the sound first, Nasim or Nicola?b Explain your answer to part a.

8Lb4 Comparing frequenciesAnimals and instruments can produce a wide range of sounds with varying frequencies. Some animals can hear frequencies of sound that humans cannot hear.

1 a Which instrument can produce the lowest pitch?b Which instrument can produce the highest pitch?c Which instrument has the widest range?d Why does the midi system have the widest range of frequencies?

2 Plot a chart like the one above to show the frequencies in the table. Use two colours (or different shading) to show the pairs of values.

Animal Frequencies they can make (Hz)

Frequencies they can hear (Hz)

cat 750 – 1600   60 – 65000

dog 450 – 1000   15 – 50000

robin 2000 – 13000  250 – 21000

human  80 – 4100   20 – 20000

grasshopper 7000 – 10000  100 – 15000

bat 10000 – 120000  1000 – 120000

a A dog whistle has a frequency of 25 000 Hz. Which animals can hear it?b Why do dog owners use a whistle that they can’t hear?c Which animal has the widest hearing range?d Which animal can produce sound waves with the lowest frequencies?e Which animal can make and hear sound waves with the highest frequency?f Which animals hear a wider range of frequencies than humans?

8Lb3 Vibrations, pitch and frequency

1 Complete the sentences using words from the box. Some words can be used more than once.

All musical instruments make a sound because something _______________ . Instruments like violins produce a _______________ pitched sound. This means that the strings are vibrating at a high _______________.

An oscilloscope can show a sound wave on a screen when it is connected to a _______________. When the waves on the screen are very close together they show that the sound waves have a high _______________. Waves which are far apart show sound waves with a _______________ frequency.

The frequency of a sound wave is the number of _______________ that pass a point every second. The loudness of a sound is shown by the _______________ of the waves. Half the height of a wave is called the _______________ . The bigger the amplitude of the wave the_______________ the sound.

The unit for frequency is the _______________ (Hz). A frequency of 50 Hz means that 50 _______________ pass every second.

amplitude frequency Hertz height high lower louder

microphone vibrates vibrations waves

2

A B C D E

a Which two sounds have the same loudness or volume? __________________________

b Which sound wave has the highest frequency? ________________________________

c Which sound wave has the lowest frequency? _________________________________

d Which sound wave has the lowest pitch? ____________________________________

e Which sound wave is twice as loud as the sound in D? __________________________

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