Light and Sound. Key Stage 2. Teachers Notes.

Transcription

1 Light and Sound Key Stage 2 Teachers Notes

2 Light and Sound Kit Lesson Plans TABLE OF CONTENTS How to use this kit... 3 Activity one Could you hear more if you could move your ears?... 4 Activity two How does your voice work?... 8 Activity three How does sound travel? Activity four Can you reflect sound? Activity five What is the difference between high and low notes?. 20 Activity six What makes a note low or high? Activity seven Can you see around corners? Activity eight How does a mirror change an image? Activity nine What happens when you mix coloured lights? Activity ten Can you change the shape of a shadow? Activity eleven How do reflections work? What I Learnt sheet...48

3 How to use the Key Stage 2 Light and Sound Kit Setting up the Kit Place the Light and Sound Kit trays on tables. The tray activities that require a mains power supply have a symbol of an electrical plug on the vertical back panel. These tray activities have a socket underneath the base panel. You may wish to remove the kit accessories that are held in with elastic cords, as the pupils may not be able to do this. What to do The Light and Sound Kit consists of 11 activities developed for Key Stage 2 pupils. Each activity has easy-to-follow instructions incorporated into the tray. The kit is designed to be used in a session of about an hour. It is recommended that children work in pairs, spending around five minutes on each activity. Teachers Notes This booklet contains extensions for each activity. These can be used for extended sessions with the kit or for more able pupils to further develop their knowledge and understanding. The extension activities utilise question and answer sequences, directed tasks and self-directed learning to facilitate the development of scientific enquiry skills: prediction, observation, measurement and recording of data. Skills Framework The kit also develops the following elements of the Skills Framework: Developing Communication Developing Number Developing Thinking Personal Social Education Risk Assessment Techniquest has fully risk assessed these activities. A full copy of this risk assessment is available on request. 3

4 Could you hear more if you could move your ears? Try this Put on the headphones. Which pair of headphones help you hear most? Can you think of any animals that can move their ears? How do you think this helps them? Pupils put on a pair of headphones fitted with hoses ending in funnels. They point the funnels towards or away from sources of sound to investigate whether they could hear more if they could move their ears. They then try a second headset with fixed funnels to see the difference. This activity works particularly well in pairs or with small groups. The pupil wearing the headphones with flexible hoses can close his or her eyes, while a partner calls or claps from various directions. The first pupil turns the ears to identify the direction of the sound. Pupils are then asked to think of animals that can move their ears and to consider how this may be useful to them. Ear size may also be considered. 4

5 Could you hear more if you could move your ears? Evaluate Listen to the sounds around you. Now, put the headphones on. Listen. Does it sound different? How? Point the funnel ends towards a noise. Does the sound change? How? Why do you think it sounds like this? 5

6 Classify and Identify Make a list of animals that can move their ears. Pick three of these animals. How does moving their ears help them? Animals can be sorted into different groups. Could any of these groups explain why some animals can move their ears? How? How does moving their ears help animals to survive in the wild? predators and prey mammals and birds warm blooded and cold blooded large and small Reflect What have you learned about how sound travels? If you have time... On a separate sheet, design a super ear for a robot. What should it be able to do? What shape should it be? What should it be made of? 6

7 Could you hear more if you could move your ears? Teachers Information Animals can move their ears by using muscles, in just the same way that they move their limbs, blink, open their mouths and so on. The muscles are under the skin and are attached to the bones of the skeleton. When the muscles contract (get shorter) they cause movement. If you want to feel a muscle doing its work, put your left hand on your right arm, just above the inside of your elbow. Now bend and straighten your right arm and you will feel the muscle moving under the skin. The reason that animals move their ears is to focus on sounds, enabling them identify the direction the sound is coming from. Prey animals are more likely to be able to move their ears than predator animals. This is a survival technique. Prey animals need to know exactly where sounds are coming from, in case they are being hunted by a predator. It does not necessarily follow that animals with larger ears have better hearing than animals with smaller ears. In many cases, as with elephants, for example, animals have large ears at they flap to keep them cool. 7

8 How does your voice work? Try this Hold the wand to your neck. Hold the button down and pretend to speak. Don t whisper. Just form the shapes with your mouth. What is missing? How does the wand make the sound? Pupils press the wand, an artificial larynx, to their necks. They press the button and mouth words. An artificial voice is produced. This astonishing effect, experienced via their own throats, helps pupils recognise that sound requires a medium. This is a strongly cross-curricular activity, with links to human physiology and disability issues. 8

9 How does your voice work? Evaluate Try the artificial voice wand. What can you feel on your throat? Predict What do you think vibration has to do with sound? Plan Your vocal cords are like small elastic bands stretched inside your throat. Using elastic bands and a peg board, design a model to show how you think your vocal cords work. Draw your model below and and find a way to show the vibration. 9

10 Develop Carry out your plan. Make a log of your investigation below. What do I know about sound and vibration? What do I want to know? How did I learn it? What have I learnt? Reflect For your model, you could pluck the elastic bands to create sounds. What do you think vibrates your vocal cords? If you have time... The artificial voice wands are used by people who have a disability that affects the larynx (or voice box). On a separate sheet, explain some of the other ways in which people who can t speak are able to communicate. 10

11 How does your voice work? Teachers Information First, you have the impulse to speak. This signal comes from the brain. You then breathe out, removing some of the air from your lungs. This breath travels upwards to your larynx (voice box); this is located in your throat. When you are not speaking, the breath passes through your voice box without creating any sound. This is known as quiet breathing. But when you want to speak, the vocal cords are pulled close together by the tiny muscles in the larynx. When the air hits these vocal cords, they vibrate. At this point, the voice is just a buzz a bit like the noise you make when you put your lips together and blow a raspberry. This buzz sound made in the larynx is amplified by the spaces in your mouth and upper throat. These are known as resonating cavities. The sound is enhanced by vibrations in the bones of your skull and other parts of the body. The words are shaped by your tongue, lips and soft palate. These are known collectively as your articulators. These combine to create your unique voice. This is all done without us thinking about it. We feel the need to speak and the voice follows. However, sometimes people can experience problems with their voices. One of the main reasons is because the voice has been strained, for example, after shouting at a football match. People who use their voices as part of their work are more likely to experience problems. For example, teachers sometimes develop vocal problems after years of talking over classroom noise. 11

12 How does sound travel? Try this Place one of the pots on the black post. Now, place one of the rods on the post and put your ear to the other end. Which rod works best? How does the rod carry sound? Now, try using your arm, instead of the rod. Pupils see a familiar MP3 player inside the tray. They know that they cannot hear music from an MP3 player without earphones or other additional equipment. Imagine their surprise when they find they can use a small pot to transmit the sound. They are next asked to substitute a rod or tube for the pot and to listen. Finally, pupils try transmitting the sound using their forearm in place of the rod. The clear message is that sound needs a medium. 12

13 How does sound travel? Evaluate How many different ways can you find to listen to the MP3 player? Which material transmits sound best? Worst? Predict Do you think soft materials or hard materials would make a louder sound when you hit them? Why? What about smooth materials and rough materials? Why? Plan Make your own plan to test: 1. Whether hard materials or soft materials transmit sound better. 2. Whether hard materials or soft materials absorb sound better. 13

14 Develop Use your plan to test some materials. Record your results below. HARD MATERIALS SOFT MATERIALS Transmit Sound Well Absorb Sound Well Reflect Which materials would you use if you wanted to sound proof a sports hall? Why? Sound travels through solid objects better than it travels through air. What have you experienced that shows this? If you have time... On the internet, research how sound travels through air. Use a new sheet to make a diagram showing how the air vibrates when it transmits sound from a source to your ear. 14

15 How does sound travel? Teachers Information Sound is a form of wave energy. When an object vibrates, it causes compression waves in the air. Compression waves are waves with vibrations along their direction of travel. These waves move away from the object as sound. Imagine dropping a pebble into a pool of water. Ordered rings or ripples spread out from where the pebble was dropped. The distance between each of these ripples or disturbances is known as wavelength. When an object vibrates, it causes the air molecules around it to vibrate also. These molecules then collide with other surrounding molecules and transfer their energy, causing these air molecules to vibrate too. These in turn cause the air molecules surrounding them to vibrate, producing a sound wave. For us to hear these sounds, the waves have to travel through the air to our ears. Your eardrum vibrates from sound waves enabling you to sense them. Sound can be transmitted through solids, liquids and gases. Sound waves travel the fastest when transmitted through solids. This is because the molecules in solids are really tightly packed. Therefore, they are always in a fixed position and can only vibrate in a fixed position, sending sound waves along its path very fast. This is similar to a domino effect. In liquid, the molecules are constantly moving and so changing their position. They are not as dense as in a solid. The molecules vibrate and collide with other molecules over a short range. Because of this, sound travels slower through liquids. Gas molecules have very high energy and are significantly less dense than in liquids or solids. They can vibrate and move freely and randomly in all directions. Gas molecules must move quite a distance before they collide with other molecules. Sound energy cannot move as quickly when the molecules are not in contact with each other. Therefore, since gas particles are very far apart, sound waves will be much slower than those passing through liquids and solids. 15

16 Can you reflect sound? Try this Hold down a yellow button. Bring the Echo Locator near an object. What happens? Try walking around with the Echo Locator. How does it warn you not to bump into things? Could you use the Echo Locator to walk around in the dark? Which animals use echolocation? Pupils press a button and move the Echo Locator around. Beeps start slowly and occur faster as the Echo Locator nears an object. Now, pupils are invited to walk about with the Echo Locator and listen to the beeps as they approach various objects. In daily life, pupils come to understand that mirrors and other bright surfaces reflect light. With this activity, they become aware that objects also reflect sound. They can then investigate what qualities of an object affect how well it reflects sound and try to predict what types of objects and surfaces will reflect sound best. 16

17 Can you reflect sound? Evaluate Hold the Echo Locator in both hands. Move it towards an object. What happens? Why do you think that is? Predict Do you think sound can be reflected? Plan Make your own plan to test: 1. How the Echo Locator works in a wide open space. 2. How the Echo Locator works in a small closed space. 17

18 Develop Test the Echo Locator in a wide open space and in a small closed space. Make a log of your investigation below. What I observed in the wide open space. What I observed in the small closed space. What I have learnt about echo locators. Reflect How could blind or partially sighted people benefit from this kind of machine? Why might a guide dog still be a better choice for a walk to the shops? If you have time... Research animal echolocation. On a separate sheet, list the mammals and birds that use echolocation. Choose one and draw a diagram to show how that animal uses echolocation. 18

19 Can you reflect sound? Teachers Information Echolocation is a biological type of sonar used by some animals to locate objects. They send out sound waves which they create by using their mouth or nose. When the sound goes out it hits an object and an echo bounces back. From this echo, the animal can identify the location, the size, the shape and even the texture of the object. Because of this, echolocation is used for navigation and for foraging or hunting. For example, bats use echolocation to move around in the dark and to find food. These sound waves are very high-pitched, and most humans are unable to hear them. A number of different animals use echolocation. Most whales, dolphins and porpoises use echolocation to identify their location and to find prey, such as shoals of fish. Occasionally, these animals can become confused and receive incorrect messages from the echo. This can result in them swimming many miles off course. For example, in January 2006 a bottlenose whale swam up the River Thames in London. It is possible that the whale became disorientated by military sonar tests. Some species of shrew also use echolocation, but unlike bats they simply use it to find their way around rather than to find food. Two types of bird also use echolocation like bats, for navigating through caves. 19

20 What is the difference between high and low notes? Try this Try singing a high note loudly. Now, try singing it softly. Trying singing a low note softly. Now, try singing it loudly. What do you see on the screen, when you sing the notes? Can you think of something that makes a high pitched sound? Can you think of something that makes a low pitched sound? Pupils sing into the machine and see volume reflected in the height of the red bars, while the pitch of the notes is registered along the horizontal axis. Young pupils find it difficult to distinguish between high pitch and loud volume, low pitch and soft volume. This activity gives them visual feedback to develop that understanding, using the dancing bars of light. 20

21 What is the difference between high and low notes? Evaluate Sing a note. What happens? Change the note you sing, higher or lower. How does the trace change? Predict What do you think will happen to the trace if you sing a note loudly? What do you think will happen to the trace if you sing a note gently? Plan Make your own plan to test: 1. What will happen to the trace if you sing a high note or a low note loudly. 2. What will happen to the trace if you sing a high note or a low note gently. 21

22 Develop Use your plan to test the notes. Draw the traces below. HIGH NOTE LOW NOTE Loudly Gently Reflect How could a singer use this machine to improve their singing? Would this be better than using a singing coach? If you have time... Research what is meant by vocal range. Find out what singers do to improve their vocal range. Record your findings on a separate sheet. 22

23 What is the difference between high and low notes? Teachers Information Your vocal range is the upper and lower limit that you can reach while singing comfortably and without straining yourself. All professional singers carry out warm up exercises for their vocal cords. Singing scales or short repetitive tunes that stretch all of your vocalisation body parts can be used as a warm up. Singers can practice to extend the upper limit of their voice and sing higher notes. To do this, they first identify their current upper limit. They first practice making this note stronger, before moving on to extending their range. This is done by working the various parts of the body that affect the sound of a high note. This high note is often referred to as a head voice because you can feel the vibrations of that note in your head, mouth and sinuses. They start by concentrating on their diaphragm to make sure they are holding a steady note and have enough breath to push through for a deeper sound. Singers also practice their posture and breathing, often using a mirror to observe themselves. They then focus on other parts of the body used for singing. This is all practised over and over until the vocal range is stretched. Singers may also want to learn to sing lower notes, although this is not as common as trying to reach higher notes. Again, a warm up is essential. Singers then find their current lower limit where they can sing comfortably without straining. This is known as your chest voice as the vibrations from this sort of singing come from deep in your chest and not your throat or head. Singers again focus on their breathing. It is easy to lose your breath when singing low notes as you open up your throat wider and often breath harder to produce a more audible and stronger sound. The diaphragm muscles need tightening as you breathe out. Again, the more this is practiced, the easier it becomes to reach the lower notes. 23

24 What makes a note low or high? Try this Use the rubber paddle to hit the ends of the tubes. Try singing the sounds the tubes make. Which tube makes the lowest note? Which tube makes the highest note? What makes a note higher or lower? Young pupils find it difficult to compare notes of different pitch. When asked which note is higher or lower, they find it very hard to say. In this activity, we have four flexible tubes of different lengths. The ends of the tubes are fixed in a frame, with a sound plate that pupils strike with a rubber paddle to produce a sound. Pupils are invited to sing the notes that they produce, so that they can feel them in their own bodies. In this way, they recognise the tighter feel of the high note, the looser feel of the low note. They can then compare the length of the tubes and work out what makes a note higher or lower. 24

25 What makes a note low or high? Evaluate Try the activity. Pitch means how high or low a note is. Which tube of air produces the highest pitched note? Which produces the lowest pitched note? Based on your findings, what do you think is making the pitch lower or higher? Predict Would you get the same findings if you plucked different lengths of elastic bands? Plan Using elastic bands and a peg board, design a model to test how you can make high notes and low notes. Think about how you will make this a fair test. Draw your model below. 25

26 Develop Choose one of the elastic bands and try to make its pitch higher. How can you do it? Does this affect how loud the note is? How can you make the note louder? Does this change the pitch? Reflect What determines the pitch of the note made by an elastic band? How is this similar to what determines the pitch produced by a tube of air? Use the caterpillar to record how you learned about pitch and loudness. If you have time... Research how a guitar works. What changes the pitch of the notes? How similar do you think this is to your model? Record your findings on a separate sheet. 26

27 What makes a note low or high? Teachers Information Like any instrument, a guitar produces sound from vibrations. Guitars vibrate because of the taught strings that are plucked by the player. The strings transfer vibration to the wood of the instrument, which projects the vibration as sound. The strings are made of metal, usual steel with a small coil of nickel or bronze wrapped rightly around the bass strings. The thin strands of metal are stretched tightly across the guitar neck and supported by a piece of plastic on the neck called the nut, and by a metal piece on the body of the guitar, called the bridge. When the strings are plucked, they vibrate along their entire length in a certain frequency, the pattern of vibration that produces a musical note. But the sound produced by the strings alone is not loud enough to be heard clearly. The guitar body amplifies the sound. The body of an acoustic guitar is comprises up to six pieces of wood. The wood pieces are very thin and usually made of a soft coniferous wood like spruce or cedar. The thin pieces pick up vibrations very easily and the box shape enables the wood to transfer the vibrations to the air inside the guitar, creating sound. The vibrating air is then forced out of a hole in the top of the body and the sound is amplified outside of the guitar. The strings can be tuned to certain notes because of their limited length, so all that is needed to make different notes is to change the length of the vibrating string. The guitar uses frets, thin pieces of metal attached the guitar neck, to limit these string vibrations. When a player pushes a string down just behind a fret, the metal stops the string from vibrating behind it, changing the frequency and the musical note produced. Very exact calculations and measurements are needed to arrange the frets, since very slight adjustment can cause the guitar to play out of tune. 27

28 Can you see around corners? Try this This is a game for two, so take turns. Player one hides the dragon among the trees and houses. Player two uses the periscope to hunt the dragon. Player two can also use the mirror blocks. How do the periscope and mirror blocks help you see around corners? This is a game in which pupils learn how light travels. Partner one hides the dragon among the trees and houses. Partner two looks through the periscope and uses the mirror blocks to see around corners to find the dragon. Through this activity, pupils develop an understanding that light travels in straight lines and can be reflected at various angles. 28

29 Can you see around corners? Evaluate Can you hide the dragon using only one house and one tree? How useful are the mirror blocks when finding the dragon? Why? Can you place the pieces so that the dragon cannot be found? Predict What would happen if you move the periscope closer or futher away from the pieces? Plan Make your own plan to test: 1. What you will see when you move the periscope closer to the pieces. 2. What you will see when you move the periscope further away from the pieces. 29

30 Develop Using your plan, test the periscope. Record your findings below. What I observed when I moved the periscope closer to the pieces. What I observed when I moved the periscope further away from the pieces. What I have learnt about periscopes. Reflect What uses can you think of for periscopes in everyday life? If you have time... Research periscopes. On a separate sheet, list the uses of periscopes. Choose one of these and draw a diagram of it. 30

31 Can you see around corners? Teachers Information A periscope is built like and works like a telescope, with a long tube containing a mirror at each end. The mirrors are fitted into the tube so that they are parallel to each other at a 45 angle. Light always reflects away from a mirror at the same angle that it hits the mirror. In a periscope, light hits the top mirror at a 45-degree angle and reflects away at the same angle, which bounces it down to the bottom mirror. That reflected light hits the second mirror at a 45-degree angle and reflects away at the same angle, into your eye. This means the image of the view the periscope is pointed at hits the top mirror and is reflected down to the bottom mirror, enabling you to see it. Because of this, periscopes allow people to see over objects or view a scene without getting into danger. This means they have uses in the military. More complicated periscopes have extra lenses added to enlarge the image. Submarine periscopes contain this more complicated arrangement. They have reflecting prisms at the top and bottom of the tube, with two telescopes and several lenses between the two ends, and an eyepiece at the viewing end. A submarine periscope also has a thick, rigid, waterproof casing and can stand the pressure of great depths of water. In addition to submarines, tanks also use periscopes to navigate or look for enemy targets. Both of these vehicles have periscopes which can be raised or lowered, as well as turned around in a 360 circle. In the 1430s, pilgrims used periscopes to see over the heads of the crowd at a religious festival in Germany. 31

32 How does a mirror change an image? Try this Look into the mirror and try to trace the red line with your finger. Why is it so difficult? Does it get easier the more you practise? How is the reflection different from the real line? Pupils trace a maze path in a mirror and find that it isn t easy at all. Every time they stray off the path, a buzzer sounds. The pupils investigate and find that the mirror has reversed the image. Pupils investigate whether it becomes easier to follow the line with practice. They can go on to investigate why this might be. 32

33 How does a mirror change an image? Evaluate Look at the red line in the mirror. How easy is it to follow with your finger? Why is this? Predict What will happen if you practice following the line a number of times? Plan Develop a training plan for completing this activity. How many times will you repeat it? How will you measure success? 33

34 Develop Follow your plan. Record your findings below. The first time I tried the activity, I found that... I followed my training plan, which involved... After training, when I did the activity again, I found that... I have learnt that... Reflect From your experience with mirror drawing, how successful do you think you would be using your non-writing hand to do the activity? Why? If you have time... Why do you think scientists investigate mirror writing? What could they be trying to find out? 34

35 How does a mirror change an image? Teachers Information Mirror drawing is a motor skill, a physical skill, like painting, writing, walking or playing an instrument. Mirror drawing tasks are used by psychologists to study learning of new skills and the effects of practice. Mirror drawing is a counter-intuitive task. When you see the mirror image it is reversed from the real image, the top is now the bottom. This makes it very difficult to trace the drawing as your brain cannot easily interpret the image as reversed. Your previous learning and experiences interfere with the activity and often you will move your finger downwards when you need to move it up, and vice versa. It becomes particularly difficult when you have to change direction. With some practice, however, most people show a dramatic improvement in their performance on mirror drawing tasks. This is usually demonstrated by timing how long it takes to complete the outline or by counting the errors made while tracing. Some studies show that people may perform better at mirror drawing when they use their non-writing hand. 35

36 What happens when you mix coloured lights? Try this Experiment with the red, green and blue light. How do you make purple light? How do you make white light? What other colours can you make? This activity looks like a Venn diagram with red, green and blue light sources ranged around a central well. Pupils try mixing the (additive) primary colours to see what colours they can produce. They quickly acquire knowledge of mixing coloured lights, forming an early understanding of concepts that will be developed at Key Stage 3. 36

37 What happens when you mix coloured lights? Evaluate How many different coloured lights can you make? Predict Using combinations of two lights, predict what colours will be produced. Plan Make a plan to test your prediction. 37

38 Develop Carry out your plan. Record your observations below. HIGH Red Green Blue Red LOW Green Blue Reflect Use the caterpillar to record how you learned about coloured lights. If you have time... Find out about rainbows. When are you most likely to see rainbows? Why do they appear? What does this tell you about sunlight? 38

39 What happens when you mix coloured lights? Teachers Information White light is made up of different colours of light. Mixing light is not like mixing paint. The three primary colours of light are red, blue and green. By combining pairs of these colours, we get the secondary colours of light. Red + green = yellow Red + blue = magenta Blue + green = cyan When all three primary colours are combined, we get white light. Sunlight is white light. By passing white light through a prism, you can see the visible spectrum, all of the colours from red to orange, yellow, green, blue and violet. Some species can see beyond the visible spectrum. Some bees and other insects can see ultra-violet, which helps them find nectar in flowers. We can see the visible spectrum in mornings or afternoons when it has been raining and then it is very bright and sunny. In these conditions, we can see rainbows. A rainbow is an optical and meteorological phenomenon that occurs when the Sun shines through droplets of moisture in the Earth s atmosphere. We see a multicoloured arc, with red on the outer edge changing to violet on the inner edge. The rainbow is actually a complete circle rather than an arc, but we only see the top half of the circle because the horizon cuts it off. 39

40 Can you change the shape of a shadow? Try this Press the buttons to try different patterns of light. Try to make the elephant s shadow taller than the bird s. Try to make the bird s shadow shorter than the dog s. Can you think of two ways to make a shadow taller? Pupils operate flashing lights in various sequences from three small towers. They observe shadows growing and shrinking as the height of the light source changes. Pupils explore different ways to make a shadow taller. Pupils can extend their learning by investigating how the angle of light from the Sun varies at different times of day and measure this with their own shadows. 40

41 Can you change the shape of a shadow? Evaluate Select one of the pieces. Use the centre light only. How can you change the shape of the shadow? Line up the four animal pieces. Can you make their shadows the same scale as in real life? Which animal should have the smallest shadow? Which animal should have the biggest shadow? Predict What shadows will be made when the two end lights are switched on, but the middle light is off? What shadows will be made when all three lights are switched on? Plan Make your own plan to explore the shadows cast using different combinations of two or more lights. 41

42 Develop Follow your plan and explore the different combinations of lights. Record your observations below. What I observed when two lights were used. What I observed when three lights were used. What I have learnt about shadows. Reflect What shadows would be made if a fourth light was shone on the objects? What shadows would be made if a light was shone on the objects from directly above? If you have time... Research how shadows can be used to tell the time. On a separate sheet, draw a diagram to show one of these ways. 42

43 Can you change the shape of a shadow? Teachers Information The Earth spins around an imaginary line called its axis, which runs through its centre from the North Pole to the South Pole. The Earth s axis is always tilted at the same angle. As the Earth rotates, the Sun appears to move across the sky from east to west and casts a shadow as it does so. It reaches the apex of its arc at midday. At this point, the Sun is directly overhead and shadows are at their shortest. As the Sun rises or sets, it is lower in the sky and so the shadows cast are much longer. In the northern hemisphere, the shadows cast by the Sun move in a clockwise direction. We can use a sundial to tell the time by reading the shadow cast by the Sun. Most sundials have a raised piece of metal or stone called a gnomon. From the gnomon are drawn lines representing the hours through the day. As the shadow of the gnomon moves over these lines we can read the time. The dial has to be aligned with true north in order to work accurately. Telling time by the Sun is an ancient method of time keeping. Many different civilisations around the world used the Sun to tell the time. The Ancient Egyptians had shadow clocks. Before they developed these, they built obelisks to cast shadows on the ground showing the time; the earliest of these dates back to around 3500BC. Both the Roman and Greek civilisations also used sundials. 43

44 How do reflections work? Try this Look at the circles and hearts in the curved mirror. Take a turn drawing on the grid with the marker. Can you draw a shape that looks like a square in the mirror? Why does the curved mirror change the shapes? Wipe the grid clean for the next user. Pupils observe how simple stretched shapes (circles, diamonds and hearts) are corrected by the curved mirror. They then try drawing their own shapes for the mirror to correct. The unexpected effects produced by the curved mirror encourage pupils to think more about the process of reflection and explore how light travels. 44

45 How do reflections work? Evaluate Draw a shape on the grid. How is the mirror image different from your drawing? Why do you think this is? Plan How would you draw shapes so that they appear correct in the mirror? How would you draw shapes so that they would appear correct if the mirror curved inwards? 45

46 Develop Draw shapes or pictures on a piece of paper. Experiment with a piece of mirror film. Record how the shape of the mirror changes the reflections. Mirror stretches image Mirror squeezes image Mirror curves inwards (concave) Mirror curves outwards (convex) Reflect Mirrors are sometimes used to help drivers see around a dangerous bend. What kind of mirror would you use for this purpose? When you curve the mirror, how does the size of the image change? What problems could this cause for drivers? If you have time... Research other uses for convex and concave mirrors. Record your findings on a separate sheet. 46

47 How do reflections work? Teachers Information This exhibit uses a technique called mirror anamorphosis. Anamorphosis is a form of art that was first experimented with during the renaissance when artists began to learn about perspective, but became very popular in the Victorian era. It involves distorting an image so that it is unrecognisable unless viewed from the correct angle. In the beginning of the 17th century, artists painted even more severely distorted pictures, leaving a round circle in the middle. When a cylindrical mirror was placed over the circle, the picture was revealed. This is the technique used here. To draw an anamorphic image, artists first draw the image in a square grid. They then use a grid in the shape of a fan. This grid has the same number of blocks across and up as the square grid. The artists then transfer the part of the drawing in each grid reference from the square grid to the fan grid. As the blocks in the fan grid are not squares but parallelograms, this adds the distortion to the image. Transferring the pattern onto the curved grid requires patience and skill. How does the mirror restore the image? A key feature of mirrors is that the angle that light hits the mirror is the same as the angle that light is reflected from it. Images reflected from flat mirrors look like the real objects. When the mirror is curved, for example, like mirrors in a fun house, the reflections become distorted. Because we use a cylindrical mirror, the image is reversed left/right. 47

48 What I Learnt... Activity name: What was the most interesting part of this activity? What is one thing that surprised you about the activity? Would you like to do this activity again? Why? 48