Grade 7_Sound Waves

Chapter : 6

Earth Physics

Ms Wida N Agustina

A. Sound Waves

Keywords

• speed of sound: a measure of how fast a sound wave travels; depends on the medium

• backwards and forwards: repeated movement in straight lines and in opposite directions

• loudness: a measure of how easy a sound of a certain pitch is to hear; loud sounds are easier to hear than quieter sounds

• pitch: the highness or lowness of the tone of a sound, for example musical notes of high pitch are higher in the musical scale than those of low pitch particles: smallest parts of a substance sound

• wave: vibrations of particles parallel to the direction of transfer of sound energy

• medium: the substance that a wave passes through

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Open Ended

Let's choose a person to sing a song!

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Where does sound comes from?

• Things that vibrate make sounds. To vibrate means to move backwards and forwards very quickly. The men in the picture are hitting drums to make them vibrate. When the drums vibrate, the drums make a sound.

• Loudspeakers produce sounds from television, radio and music players. If you put small objects into the paper cone of a loudspeaker, the objects will bounce around. This shows that the paper cone in the loudspeaker is vibrating.

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Draw

Draw a sound wave!

​Sound Waves

• Sound waves are composed of compression and rarefaction patterns. Compression happens when molecules are densely packed together. Alternatively, rarefaction happens when molecules are distanced from one another.

• The particles in the air are made to vibrate backwards and forwards in time with the vibrating object.

• When the particles in front of the object vibrate, those particles make other particles in front of them vibrate. This makes a sound wave.

• The speed of sound waves in air is about 343 metres per second.

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Poll

We can hear the sound on the space.

• True

• False

Sound Waves on the Moves

• Sound waves travel by making particles vibrate. Sound will travel though anything that has particles: gas, liquid or solid.

• Animals such as whales and dolphins communicate with sounds.

• The substance that the sound wave moves through is called the medium. Therefore, solids, liquids and gases can all be a medium for sound

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Vibrations in a vacuum

• To hear a sound, there must be:

  • a vibration to make the sound (Source)

  • a medium containing particles through which the sound wave can travel.

• As there are no particles in a vacuum, there is nothing to vibrate to make a sound wave.

• Therefore, sound will not travel in a vacuum. Space is a vacuum. If sound waves could travel through space, we would be able to hear the Sun!

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Let's Play!!

"Don't say the word"

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