The Science of Sound Sound waves Sound waves

The Science of Sound

Sound waves � Sound waves are longitudinal waves. Longitudinal waves comprise of a series of compressions and expansions ( rarefactions).

� Sound waves require a state of matter to travel through. � Sound can travel through solids, liquids or gases( air).

� The particles in the state of matter vibrate and carry the sound wave. � The particle vibrate in the same direction as the wave is travelling

� Sound waves are said to have a ‘bulk effect’, that means that the sound wave travels in all directions from the source.

� If no medium( state of matter) is present the compression and rarefaction of the particles cannot be formed, hence no sound wave is produced.

� Sound waves cannot travel with out a state of matter. � Therefore sound cannot travel in Vacuum. �A Vacuum is a space where there is no matter.

� Can you think of a place where there is no matter, not even air? � Outer Space !

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Reception of sound

Reception of sound � For sound to be heard, it must first go through a sequence of steps. � 1) The sound wave must meet the ear drum � 2) The eardrum vibrates at the same frequency of the sound wave. � 3) The vibrations are passed from the ear drum to 3 tiny bones in the ear (Stapes, Malleus, Incus).

� 4) The vibrations are passed onto the middle ear and then to the inner ear. � 5) In the inner ear the vibrations are converted to electrical signals � 6) These electrical signal are then taken to the brain. � 7) In the brain these electrical signals are interpreted by the brain as sound.

Activity � Question � Astronauts on the moon cannot speak to each other as they might do on earth. Explain why? � Suggest how they may communicate with each other?

Speed of sound � Sound travels at a speed of 330 m/s( in air) � Mean while light travels at a speed of 300 000 m/s � Sound � This travel substantially slower than light. is why we see things at a distance before we hear them.

� Examples � Timing a race: - This is why we start the clock as we see the flash from the gun and not when we hear the sound of the gun being fired, when timing a race from the finish line.

� Lightning and thunder: - This is why we see the lightening before we hear the rumble of the thunder.

Properties of Sound Waves � Like all waves. � Sound waves can be � Reflected � Refracted � Diffracted � Super-imposed

Reflection of Sound � Sound waves obey the Law of reflection. � i=r � The law of reflection states that the angle of the incidence is equal to the angle of reflection.

� The speed of sound varies, depending on the state of matter, the sound wave is travelling through. � Sound travels faster in liquids than in gases; � And travel even faster in solids than in liquids.

� Echoes are the most familiar example of reflection of sound.

Refraction of sound � It is easier to hear at night than during the day. This is because sound travels at different speeds at different temperatures.

Pitch � The pitch of a note is related to the frequency of the note. � The frequency of a wave, is the number of wave cycles that are produced every second.

� Soprano singers have a high pitch ( high frequency) � Bass singer have a low pitch ( low frequency)

Loudness � The loudness of a sound is associated with the amplitude of the sound. � The amplitude of a wave is the maximum displacement of the wave from the rest position.

� The greater the amplitude, the louder the sound. � The smaller the amplitude, the quieter the sound.

The audible range � Human hear sound which have a frequency in the range between 20 Hz – 20 k. Hz ( therefore threshold of hearing is 1000 Hz).

� Subsonic sounds have frequencies below 20 Hz these cannot be heard by humans, but can be heard by elephants. � Earth tremors have frequencies in this range this is why they can be felt, and not heard.

� Ultra sounds have frequencies greater that 20 k. Hz. � Again this frequency cannot be heard by humans; but can be heard by bats, bats use ultrasound to help them navigate in the dark.

� Also dogs hear at these high frequencies. � Most dog whistles produce sound within the range of 23 - 54 KHz (ultrasound).

Audible hearing range

Activity � Using your text books give 3 uses of ultrasound. `

END � Answer the assessment questions to see how much you have learnt.