Sound_Concept_1
Sound Transmission
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Subject facts
Why you need to know these facts.
Vocabulary Amazing facts
Common Misconceptions
Questions
Teaching Ideas
Subject Facts
There are a tremendous variety of sounds around us at times. They differ in a number of subtle ways, but they are all produced by something vibrating. in many cases, the exact cause of the vibrations is quite difficuit to identify. However, there are many sound-producing objects where the source of the vibrations is open to easy examination for example, musicak instruments which are plucked or struck (guitars and drums). The more Titeresting problem is explaining how these sounds travel out from the source
Sound waves
The term 'sound waves' can give the wrong mental picture,
They are not like ripples on a pond, unduiating up and down (transverse waves) and radiating out from the point where a stone fell. Imagine what a vibrating drum skin woufd look hke if it were shown in slow motion: it would be moving in and out (see Figure 1). As it moves out it pushes against the surrounding air; compressing it and making it bump' into the air next to it A usefu*lanalogy is a car running into the back of a row of stationary cars, causing them to knock into each other.
Another way of modeling sound is to hold one end of a Slinky and repeatedly flick the other end (see Figure 2): this will send compresscon pulses along its length (longitudinal waves). The pulse might even bounce back from the end, as in an echo.
On reaching the ear, these sound pulses press on the eardrum (see Sound Reception), causing you to hear them,
How sound travels
Sound pulses or vibrations can travel through most materia!s. Some materials are better conductors of sound than others, because the molecules are arranged in a way that makes vibration easier. Sound and fight are very different in this respect: sound needs a medium to travel through, but light doesn't. Whales can communicate with each other over hundreds of miles by sound pulses travelling through the sea.
' Telephones' made from tins and string can work very effectively if the string is kept taut. Iron and steel transmit sound very clearly: you can drive the rest of the school demented by tapping on the radiator (make sure it's not turned on if you are listening to the sounds).
Seeing sound
Sounds can be tuned into transverse (up and down) waves by using a microphone to transform them into electrical signals which are displayed on an oscilloscope. This is the main source of misunderstandings about what sound waves 'look like',
Why you need to know these facts
An appreciation of how sound is transmitted is fundamental to understanding the nature of sound. All further work this area wili be supported by a secure introduction here.
Vocabulary
Echo a sound reflecåon from a rigid surface such as a wall.
Oscilloscope a device for displaying in a visible farm sound waves that have been converted into electrical pulse;.
Transmission the process by which sound travels from one place to another
Vibration forward and backward movement of an object (usually very rapid).
Amazing facts
In the air at sea level sound traveis at 340 metres per second. It travels faster in water (1400ms-l ) and faster still in steel (5000ms-1),
Common Misconceptions
Sound transmission
There are relative\y few common misconceptions about sound, though misunderstandings can arise from the use of vocabulary. For example, the question How do you hear that sound? might be answered 'Because I listen carefully!' A better question to ask would be: How does the sound get from the drum to your ear? The idea that jagged lines of sound come from a noisy object (as in cartoons and comics) may confuse some children.
Sound production
Sometimes children find the link between the vibration of an object and sound difficult to make. Holding an inflated balloon in front of your face and singing humming or speaking at it will cause it to vibrate, demonstrating that sound and vibration are essentially the same thing.
Questions
Why does the sound of a car change as it goes past?
As a speedlng car comes towards you, it is 'catching with its own sound, so the sound pulses you hear are squashed closer together (higher note). As it goes away from you, the sound is 'left behind', so the pulses are drawn further apart (lower note). (See Figure 3) As a modei, imagine a conveyor belt running towards you with a person standing beside the belt further up placing chocolates on it at regular time intervals. If this person were to walk towards you while still placing the chocolates, you would start to receive chocolates more often, if the person were to wak in the opposite direction, the chocolates would arrive less often.
Teaching ideas
What happens when an aeroplane travels at the speed of sound?
The sound pulses build up in front of the moving aeroplane (a 'pile' of sound pulses all travelling together), As it goes past you will hear all of these pulses at the same time: a 'sonic boom'. In the conveyor belt model, the person is walking towards you at the same speed as the belt, piling up chocolates which all reach you just as the person passes by.
What makes a good sounding board? (exploring)
Give each group of children a tuning fork. Ask them to take turns hitting one of the prongs against the tabletop (to start it vibrating), then place the base of the fork against different surfaces in the classroom (tabletop, wall carpet and so on), Which surfaces ampfify the sound? What do these surfaces have in common? (They are all hard) Ask the children to record materials In two sets according to whether or not they amplify the sound.
Ask the children to 'listen' to a vibrating tuning fork by placing it against their head. Can they 'hear the sound better in some places than in others? Invite them to make a 'sound map' of the head NB If chiidren can 'hear' the fork better when its base is placed against the bridge of the nose or the skull behind the ear than when it is held next to the ear, they may have a hearing problem and should be referred to a doctor.
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