Unit 4P.1: Sound. How sounds are made? Loudness and pitch Hearing sound Noise Traveling of sound Echo

Transcription

1 Unit 4P.1: How sounds are made? Loudness and pitch Hearing sound Noise Traveling of sound Echo Science skills: Predicting Observing and classifying UBy the end of this unit you should: Know that sound is a vibration. Know that sound can vary in loudness and in pitch. Know that we hear sounds that travel to our ears, and we are not able to hear all the sounds. Know the importance of having two ears. Know what noise is. Know that sounds can travel through solids, liquids and gases. Know what an Echo is. 59

2 Physical processes How sounds are made? What kind of sounds have you heard today? If you live in town, you may have heard cars and buses. Maybe you heard the call to pray for Fajr? A sound is made when an object vibrates. When something vibrates it moves forward and backward. Usually you can not see an object vibrating when it makes a sound because it is moving so quickly. is made when an object vibrates During Vibration an object moves forward and backward very quickly. You can see and feel the vibration from a tuning fork when it makes a sound. 60

3 Tap a tuning fork on the side of a desk and then place the tip of the tuning fork in a container of water. The vibrations from the tuning fork will make some of the water splash out of the container. You can see the vibrations if you put rice on a duff and then hit the skin lightly. You ll see the rice grains jump around. 61

4 Key words: Vibration Tuning fork Key ideas: is a vibration Vibration is when an object moves forward and backward very quickly. Key questions: 1. Aisha was playing a duff. Explain how the sound is made. 2. What is vibration? 3. What happens to a guitar string when you pluck it? 62

5 Physical processes Loudness and pitch Loudness Changing the loudness of a sound is like turning the volume button on the television up or down. You do not change the type of sound, just whether you can hear it louder or not. You can make the sound of a drum louder by striking it harder. In that way, you give it more energy and the vibrations are bigger. If you strike it very gently, you get small vibrations and a very quiet sound. The loudness of a sound is how loud or soft it is 63

6 s of different loudness can be produced when this drum is hit: a) gently or b) hard. Low loudness (Soft sound) High loudness (Loud sound) s of different loudness make waves of different heights. s can be soft or loud depending how close to the sources of the sounds you are. 64

7 s are different depending on how close or far you are from the source of the sounds. Loudness is measured in decibels (db). The softest sound anyone can hear is 0 db. O db - Falling snow 3O db - A soft whisper 5O db - Quiet talk 7O db - Television 10O db - Subway train entering a station 11O db Chain saw 12O db Loud rock music 14O db Jet engine at takeoff from 30m (100ft) 65

8 Pitch Pitch: How high or low a sound is. A big drum makes a big, deep sound we say the sound is a low pitch. A small drum makes a much deeper sound we say the sound is a high pitch. It does not matter how hard you hit it. A high sound has a high pitch and a low sound has a low pitch. A tight drum skin gives a high pitch sound than a loose drum skin. 66

9 The thick strings on a guitar make a low pitched sound, but the thin strings make a high pitched sound. The pitch of a sound depends on how quickly the vibrations move through the air. A small instrument vibrates very quickly (a small drum or a thin guitar string) it has a high pitch. A big instrument vibrates very slowly and gives a low note. It has a low pitch. 67

10 Xylophones and chime bars make a sound when they are hit. High pitched sounds are made from the shorter bars on a xylophone or shorter pan pipes. Low pitched sounds come from the long bars of a xylophone and pan pipes. Long objects and instruments vibrate to make low pitched sounds. Pan pipes Every sound has both pitch and loudness. For example a mouse that squeaks, has a high pitch and a low loudness. An elephant makes a sound that has a low pitch but a high loudness. 68

11 Project: Using different sizes of elastics bands, try to investigate the relationship between the size and the pitch. Vary the length by moving the pencils and pluck the rubber bands. Key words: Loudness Volume Pitch Tight Key ideas: s have both pitch and volume. The volume of s can be low or loud. The pitch of a sound depends on the instrument size. Key questions 1. What is the difference between volume and pitch? 2. Which of these recorders would you expect to make the lowest sound (pitch) and why?.. 69

12 3. Aisha knows that if she wants to change the pitch of the drum she needs to tightened or loosen the drum skin. What would happen to the pitch of the sound if she tightened the skin?.. 4.Arrange each set of instruments in order of pitch by writing 1, 2 or 3 in the box below each picture (1 making he lowest- pitched sound) 70

13 4.15.3, Physical processes Hearing sound We hear sounds when the vibrations travel from the objects to our ears. Do you know how we hear the sounds? s go into our ears and make our eardrums move. This tells our brain that we have heard a sound. It is important never to poke things in our ears, because we can hurt them easily. Our ears tell us where the sound is coming from. If a friend who is standing to your left calls your name. The sound reaches your left ear first then it reaches your right ear. The brain can tell you that the sound is louder to the left ear and it tells your head to turn left to see 71

14 your friend. Having two ears helps you know where the sound is coming from, even if you were blindfolded. Having two ears helps us to tell where the sound is coming from. s we cannot hear Many animals have better hearing than we do. Dogs have very sensitive hearing; they can hear higher pitched sounds than we can. The dog owners have a whistle that only dogs can hear the sound from it. Elephants can hear lower pitched sounds that we can not hear. 72

15 There are some sounds that are either too high or too low for us to hear. Key words: Hearing Eardrum Ears Whistle Key ideas: We hear sounds when they travel to our ears. Having two ears helps us tell where sound is coming from. There are sounds that are either too low or too high for us to hear. Key questions: 1. How do we hear sounds? 2. Why must we never poke things in our ears? 3. Can we hear all the sounds? Explain! 4. Why do humans have two ears and why are they at the side of head? 73

16 Physical processes Noise Noise can almost be any sort of sound, but the word is especially applied to unwanted or unpleasant sounds. The sounds of traffic and construction work in the city are noise. The louder they are, the worse the noise. Even your favorite music can be noise if it distracts you while you are studying. counts as noise if it is so loud that it becomes painful to hear, or even damages your sense of hearing. 74

17 Very loud sounds can be dangerous as they can damage your ears. In order to protect their ears from noise, workers wear earmuffs when they are working with loud machinery. travels through materials better than others, so the material for earmuffs is chosen carefully to keep the sound out. 75

18 Activity Which material would be the best to make earmuffs? Some children decide to investigate which material would be the best for making earmuffs to stop sound reaching their ears. The children planned an investigation for testing five different materials as earmuffs: cotton wool, paper towel, carpet, plastic bag and bubble wrap. They made a pair of earmuffs using a hair band and rings of cardboard. The different materials could be stuck to the cardboard rings. The children chose one person to wear the earmuffs. This person had to walk away from a buzzer until she could not hear the noise any longer. The distance between the person and the buzzer was measured. The children did this test using each different material in the earmuffs. Which materials made the best earmuffs? 76

19 Key words: Noise Damage Earmuffs Key ideas: Noise is an unpleasant or very loud sound. Loud sounds can damage the ears. People who work where there is a lot of noise wear earmuffs to protect their ears. Key questions: 1. Cross out the wrong word in each sentence. (Very loud/quiet) sounds can be dangerous as they can damage your ears. Noise is an (pleasant /unpleasant) sound 2. How can hearing be damaged? 77

20 3. Roza and her group carried out an investigation into which material is best for sound proofing. They wrapped a ticking clock in a series of different materials in turn, and placed it inside a box each time. Here are their results. Material Volume of sound recorded by computer sensor Paper 6 Cotton wool 2 Aluminium foil 7 Bubble wrap 1 a. Which material was the best for sound proofing? How do you know? b. Which material was the worst for sound proofing? How do you know? 78

21 Physical processes How sound travels travels in waves moves through the air in waves. These waves are invisible, but we can see how they might look with a special instrument called an oscilloscope. We normally think of sound waves as traveling through the air, but the truth is that they can travel through solids, liquids and gases. waves travel by making particles vibrate. travels though air When somebody talks, the vibration travels through air to reach your ears. 79

22 The vibrations make the air around the instrument vibrate too. The vibrations made by the guitar strings, drum skin and triangle make the air vibrates. When these vibrations reach our ears, we hear them as sounds. Ask you teacher to put a candle on and place the flame near a speaker as you turn the volume up you ll see the flame vibrate more! If you put it so loud the flame can go out! travels though water travels in water, next time you go to swimming try to talk to your friend under the water. 80

23 travels though solids s travel well through solids. If you are sitting at a table, place your ear on the table. Stretch out your arm and tap the table very gently with one finger. Even though this tap is a very quiet sound, you can hear it clearly as the sound vibrations travel through the table and enter your ear. Activity: Making a String Telephone Carry out investigations to find the answers to the following questions: Which material is the best for making a telephone wire? (thick or thin string? Plastic or fabric?) Which is the best container to use for a telephone? (tins, or plastic cups?) 81

24 Question: (What are you testing?) Procedure: (Describe the experiment) Materials: (List what you used) Observations: (Record what happened) 82

25 Results: (Make your own data table) Conclusions: (Use your observations and results to describe what you learned) 83

26 Insulation insulation is the prevention of transmission of sound. The actual process of sound insulation involves inserting some type of insulating material into the walls, as well as above the ceiling and below the floor. In some cases, this involves the use of rolls of fiberglass insulation or introducing foam insulation into the open spaces. 2T(1)2T Wall insulation 2T(2)2T Insulation under floors. 2T(3)2T Partition insulation. 2T(4)2T Roof insulation. 2T(5)2T Ceiling insulation. 84

27 Key words: Waves Travel Solid Liquid Gas Key ideas: s travel through solids, liquids and gases. Some materials muffle or stop sound from travelling are called sound insulators. Key questions: 1. What can sound travel through? 2. Is there sound on the moon? Explain? 3. In which of the following does sound travel fastest? a) Solid b) Liquid c) Gas Explain your answer? 85

28 Physical processes Echo Did you throw a rubber ball on a brick wall and it bounced back? bounces too, sound that bounces off something before reaching a listener is called echo. When you are in Villagio next, face upwards and talk loudly outside Go sports! You hear an excellent ECHO! Echo: A sound that bounces off a surface The sound that travels directly reaches the listener first then the echo is heard; that is because the sound that travels directly has less distance to travel and takes less time to travel to our ears. Sailors can use echoes to find out the depth of the sea 86

29 ULet's measure: Use a ruler and see for yourself. Have two students standing one facing each other while talking; then ask one of the students to move for some distances and measure the distance for each move. You should record the final distance where one of them could not hear the other. The distance is. Do you know bats use echoes to see in the dark. It is called Echolocation! Do the same steps for this activity, but ask one student to stand in front of the wall while talking and to move for a certain distance until an echo will be heard. Don't forget to measure the distance every time. The distance is. The longer the distance the sound needs to travel; the more time it needs to reach your ears. 87

30 Key words: Echo Bounces off Travel Key ideas: When sound bounces off a surface we have echo. Project: Design an experiment to explain why the sound that travels directly reaches the listener first then the echo is heard. Key questions: 1. Mohamad was under a bridge and he shouted his name and then heard his name echo back. Explain how the echo worked.. 2. Give one situation where an echo is useful:. 88