Light And Sound Notes PDF

LIGHT AND SOUND Mr. Mkola Jr Introduction. ▪ Things that vibrate make sound ▪ To vibrate means to move backwards and forwards or back and forth very quickly. ▪ Examples; Hitting the drums to make them vibrate. When the drums vibrate ,the drums make a sound. ▪ When a person speaks, the vib...

LIGHT AND SOUND Mr. Mkola Jr Introduction. ▪ Things that vibrate make sound ▪ To vibrate means to move backwards and forwards or back and forth very quickly. ▪ Examples; Hitting the drums to make them vibrate. When the drums vibrate ,the drums make a sound. ▪ When a person speaks, the vibration comes from the vocal cords. Definition Sound is the form of energy produced by the vibration of particles. NOTE: Whenever there is no vibration, no sound is produced. In a vacuum, there are no particles to vibrate so sound can not travel in Vacuum.  LOUDNESS OF SOUND ▪ The loudness of sound is increased by applying more force to vibrate an object. ▪ A drum produces a louder sound when you hit it harder. ▪ A guitar produces a louder sound when you pluck it harder. ▪ Therefore the more the hitting strength the louder the sound.  PITCH OF SOUND ▪ The pitch of sound is how high or low the sound is. ▪ A high pitched sound is thin and soft while the low pitched sound is broader and thick. ▪ Example ; Thunder makes a sound with a low pitch while a baby crying makes a sound with a high pitch. ▪ A high pitched sound is produced by tightening the skin of the drum or the strings of the guitar. SOUND WAVE ▪ This is when the sound travels from a vibrating object to our ears. ▪ Every time an object vibrates forward, the air in front of the object gets pushed forward. ▪ 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 in air is about 343m/s. ▪ The vibrations of the air particles in very loud sounds can cause damage to the ear. ▪ The waves transfer energy from the source of the sound, e.g. a drum, to its surroundings. ▪ Your ear detects sound waves when vibrating air particles cause your ear drum to vibrate. ▪ The bigger the vibrations the louder the sound. ▪ Sound at a certain pitch can cause damaging vibrations even when the sound is not very loud. Propagation of sound waves ▪ Sound will travel through anything that has particles; gas, solid or liquid. ▪ Therefore, solids, liquids and gases can all be a medium for sound. ▪ The Speed of Sound: Sound travels at different speeds depending on what it is traveling through. Of the three mediums (gas, liquid, and solid) sound waves travel the slowest through gases, faster through liquids, and fastest through solids. ▪ why do sound waves move fastest in solids and slowest in gases? ▪ Solids are packed together tighter than liquids and gases, hence sound travels fastest in solids. ▪ The distances in liquids are shorter than in gases, but longer than in solids. ▪ Gases are the slowest because they are the least dense: the molecules in gases are very far apart, compared with solids and liquids.  vibration in vacuum ▪ To hear a sound , there must be: A vibration to make a sound. A medium containing particles through which the sound 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.  REFLECTION OF SOUND A sound wave travelling towards a wall will hit the wall and come back. Sound wave reflect best from large, smooth, flat surfaces. Surfaces such as glass, tiles , flat metals and smooth concrete give good reflections of sound. The reflection of sound wave is called an Echo.  useful echo Echoes can be useful. Bats use echoes to find insects for food. Dolphins use echo to find food. Boats can use echoes to find the depth of water under the boat. Echoes can also be used to make images from inside the body.  unwanted echoes Sometimes echoes are unwanted. When recording music , echoes change the sound. The sound repeats several times. In a theatre, the audience need to hear the voice of people on the stage. If there were echoes in a theater, the voices would not be clear.  ways of stopping echoes Window Coverings. Dampen echoing sound waves by reducing the amount of bare glass exposed in the room. Floor Coverings. Lay down large area rugs or plush throw rugs on hard floors to soften the surface and help absorb echo. Wall Coverings. Reduce home echoes even further by softening hard wall surfaces with fabric wall or soft thick curtains.  A fairly inexpensive way stop echoes is by filling up your room with tons of sleeping bags and couch cushions. Rooms filled with plush furniture and accessories help cut down on echo. Couches and plump recliners, for example, absorb sound reflection. Fabric upholstery typically absorbs sound more effectively than vinyl or leather. Even items like bookshelves filled with books and decorative items can reduce echo  QUESTIONS 1. A guitar is a musical instrument with strings. What is needed to make a sound from the guitar? 2. Zara is playing a guitar by plucking a string. Describe a way that Zara can make the sound louder. 3. Some flying insects make a buzzing sound. Describe what causes this sound. 4. Thunder can make objects inside a room vibrate. Explain what causes the objects to vibrate. 5. A fly is walking up a glass window. The fly’s feet make vibrations. Explain why people cannot hear the sound of the fly walking. 6. Why sound can not travel in a vacuum? 7. The moon has no atmosphere. People who went to the moon wore suit that contained air. The people who went to the moon worked close together. They did work such as hammering and digging. Explain why the people doing this work could not hear it happening. 8. Describe what happens to a sound to make an echo. 9. Zahra has an empty room where she can practice playing her drums. Which materials could she put on the walls to stop echoes when she plays? The End