Chapter 8.1

Chapter 8.1

Objectives

• Describe how sound waves are produced.

• Describe how sound waves travel.

• Expalin what is meant by a medium and why sound waves need it.

• Name the speed of sound in several materials and expalin why the speed of sound is different in solids, liquids and gasses.

• Describe the difference between longitudial and transverse waves and be able to recognise them.

  

2.In a loudspeaker, the part that

vibrates is the cone

3.In a guitar, the part that

vibrates are the strings

Sound is produced

by vibrations 

in a sound source. Examples of sound sorce: 1.Your vocal cords vibrate to produce sound

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Sound cannot travel in vacuum.

Sound needs material or medium to travel through, such as air, water or solid object beton, wall etc...

3) The speed of sound in steel is 5100 m/s, in water is 1500 m/s, but in air only 330 m/s,

  Copy and complete the sentences below, using these words or phrases to fill in the gaps. Some owrds or phrases are not needed.

Closer together,    Further appart,    Less,    More

• The speed of sound in water is faster than the speed of sound in air because in water the particles are ...........lthan they are in air.
• The speed of sound in air is slower than the speed of sound in steel ,in steel the particles are ............than they are in air.
• A sound made underwater will take ......... time to travel a certain distance than a sound made in air.

In a soundwave the air (or another medium) actually doesn't go up and down. 

What do the ups and down in the visual depiction of a wave indicate about the air?

In a sound wave the air gets comprsessed together and then decompresed. The peaks indicates areas of compression. The valleys indicate areas of decompression.

As seen in the image on the right.

Liam is watching fireworks at a festival. He sees a firework explode in the sky and then hears the sound 4.5 seconds later. How far away is Liam from firework?

G:

A:

C:

Liam is watching fireworks at a festival. He sees a firework explode in the sky and then hears the sound 4.5 seconds later. How far away is Liam from firework?

  

     

G: t=4.5 s,  V sound in air = 343 m/s

A:  S= ?

C:  S=v.t 343. 4.5 = 1543.5 m of 1.54 km

Calculating the speed of sound  using echoes

A girl stands 102 m away from a wall and claps two wooden blocks together. She hears an echo after 0.6 s.Calculate the speed of sound in air. 

G:  

A: 

C:

Given: t = 0.6 s. d=102 + 102 = 204 m.

Asked: v=?

v=s/t = 204÷ 0.6=340 m/s

Or v=s/t v= 102÷ 0.30 = 340 m/s