Sound Vibrations Loudness Pitch and frequency Echoes

ALL SOUND IS CAUSED BY VIBRATIONS! Investigating Sounds Put your hand on your throat and talk. What can you feel? Your throat VIBRATING. Put your hand on a loudspeaker that is producing sound. What can you feel? ALL SOUND IS CAUSED BY VIBRATIONS! The loudspeaker VIBRATING. Strike a tuning fork against a wooden block. What can you see? The prongs of the tuning fork VIBRATING. Place a ruler half over the end of a table and flick the ruler. What can you see? The ruler VIBRATING. Pluck a string on an instrument. What do you see? The string VIBRATING.

Sound and Vibrations All sound is caused by VIBRATIONS. How does sound travel from a vibrating object to your ear? The vibrating object makes the AIR PARTICLES VIBRATE. The vibrations are passed along from air particle to air particle in the form of WAVES. Sound travels in waves. The air particles make your EAR DRUM vibrate. Your ear drum makes three small bones, called OSSICLES, vibrate. These are connected to your COCHLEA that contains thousands of SMALL HAIRS. These small hairs DETECT the vibrations. The AUDITORY NERVE carries messages to your BRAIN which are interpreted as SOUNDS.

Exercise 1: Sound and Particles Which state of matter does sound travel fastest through? Why? Why can sound not travel through a vacuum? Describe an experiment which demonstrates that sound can not travel through a vacuum. Solids. The particles are closest together in a solid so it is easier for the vibrations to be passed from particle to particle. There are no particles to vibrate. Place an electric bell in a bell jar. Connect the bell jar to a vacuum pump and remove the air. When the air is removed you will not be able to hear the electric bell because sound can not travel through a vacuum.

Investigating Sound Put a squeaky toy in a plastic bag. Put the plastic bag in a bowl of water so that the bag is totally covered. Squeeze the toy. What happens? A squeaky duck Even though the squeaky toy is underwater you can still hear it. This tells you that SOUND CAN TRAVEL THROUGH WATER.

Sound and Vacuums Sound can travel through solids, liquids and gases. SOUND CAN NOT TRAVEL THROUGH A VACUUM. If you were in space you would not be able to talk as there is NO AIR TO VIBRATE. If you were in space and there was an explosion you would not be able to hear it.

Parts of the Ear Oval window Semi-circular canals Ossicles Auditory nerve Ear drum Cochlea Pinna Eustachian tube

Exercise 2: Sound What causes all sound? What does sound travel in? What are the three small bones called in your ear? What carries messages from your cochlea to your brain? What could happen if part of your ear was damaged? Vibrations. Waves. Ossicles. Auditory nerve. You may lose some or all of your hearing.

Exercise 3: Label the Parts of the Ear Below __________ Pinna Ear drum Ossicles B. A. D. Cochlea Nerve

Loudness Sound is a type of ENERGY. Which sound do you think has the most energy? A LOUD sound or a QUIET sound? The LOUDER a sound is the MORE ENERGY it has. The QUIETER a sound is the LESS ENERGY it has. As you MOVE AWAY from a sound, the QUIETER the sound becomes. The more energy you put into striking the hammer, the louder the sound. We can measure HOW LOUD a sound is using the DECIBEL SCALE (dB).

Loudness and Distance The FURTHER AWAY a sound is, the QUIETER a sound is. I can’t hear it - it’s too quiet! What beautiful music!

What are the effects of noise on your body? What is NOISE? A NOISE is UNWANTED SOUND. What sorts of noises could damage your hearing? Loud music. Machinery. Explosions. Aircraft. How can you protect yourself from loud noises? Ear protectors. NAUSEA HEADACHES LOSS OF HEARING DEAFNESS Double glazing. What are the effects of noise on your body? Putting machinery into separate rooms to workers. Turning down the volume of music.

Exercise 4: Sound Which sounds have the most energy, loud or quiet? What scale is used to measure the loudness of sound? Which is the loudest sound, 20dB or 87dB? Which sound has the most energy, 67dB or 43 dB? Give an example of a loud noise that could damage your ear. Loud. The decibel scale. 87dB. 67dB. Loud music, explosions and machinery.

Investigating Pitch I 1. Take four glass bottles of the same size. 2. Fill the glass bottles with different amounts of water. 3. Blow across the top of each bottle. 4. What happens? Lowest pitched Highest pitched The MORE AIR there is in the bottle, the LOWER-PITCHED the sound it makes is.

Investigating Pitch II 1. Place a ruler over the end of a table. 2. Strike the ruler so it vibrates. 3. Move the ruler so there is less in contact with the table. 4. Strike the ruler again. What happens? Highest pitched Lowest pitched The MORE RULER there is that is vibrating, the LOWER the PITCH of the sound it makes.

Exercise 5: Highest and Lowest Highest pitched Lowest pitched Medium pitched

Dogs can hear higher pitched sounds than humans Number of Vibrations The NUMBER OF TIMES an object vibrates every second is called the FREQUENCY of the sound. The FASTER an object vibrates, the HIGHER the frequency of the sound. The SLOWER an object vibrates, LOWER the frequency of the sound. The units of frequency are HERTZ or Hz. One hertz equals one vibration every second. PITCH is the MUSICAL equivalent of frequency. Pitch does not have any units though. HUMANS can hears sounds up to a frequency of 20 000 Hz. Some ANIMALS, such as BATS and DOGS, can hear sounds HIGHER than humans. Dogs can hear higher pitched sounds than humans

Exercise 5: Number of Vibrations? What are the units of frequency? How high can humans hear sounds? What could reduce this upper limit to sounds humans can hear? Can you name two animals that can hear higher pitched sounds than humans? What word do musicians use instead of frequency? Hertz. 20 000Hz. Loud music and old age. Dogs and bats. Pitch.

The Oscilloscope We can examine the nature of sounds using an OSCILLOSCOPE. An oscilloscope converts a sound into an ELECTRICAL SIGNAL and then displays this information as a WAVE on the SCREEN. The distance between two crests of a wave tells us the FREQUENCY of a sound. THE CLOSER TOGETHER CRESTS ARE, THE HIGHER THE FREQUENCY. The half height of the wave tells us how LOUD a sound is. THE BIGGER, THE LOUDER. You need to be able to COMPARE OSCILLOSCOPE TRACES and decide which represents the loudest/quietest or highest/lowest sound.

? ? ? ? ? Exercise 6: Which Sound? Which sound shown is the… a) Highest? _____ b) Loudest? _____ c) Quietest? _____ d) Lowest? _____ ? B B ? ? A ? A A. B.

Reflecting Sound Hellooo! Hellooo! What happens when sound strikes a HARD surface? The sound bounces back - it is REFLECTED. This is called an ECHO. Hellooo! Sounds are NOT REFLECTED by SOFT materials such as CURTAINS - they are ABSORBED. Hellooo! This is why in THEATRES and CINEMAS they have lots of curtains and other soft materials on the walls - it is to REDUCE these sound reflections. Otherwise, you would not be able to understand the talking by the actors.

Design an Investigation What is the SPEED OF SOUND? DESIGN AN INVESTIGATION that will allow you to CALCULATE the speed of sound. What APPARATUS will you need? How will you keep it a FAIR TEST? How will you ensure your results are RELIABLE? Would you like some HINTS? SPEED = DISTANCE/TIME HARD SURFACES are good at reflecting sound. STOPCLOCKS are good for recording time intervals.

Exercise 7: Sound What do we call reflected sound? Which surfaces are the best for reflecting sound? What is the speed of sound in air? Why does sound travel faster through solids than liquids? A girl is 495m from a wall. She shouts at the top of her voice. How long will it take an echo from the wall to reach her? An echo. Hard surfaces. 330m/s. The particles are closer together in solids than liquids. 3 seconds.

Revision Summary 1 All sound is caused by VIBRATIONS. Sound is a type of ENERGY and travels in WAVES. Sound travels through air by vibrating the AIR PARTICLES. Sound can not travel through a VACUUM. Sound travels fastest through SOLIDS because the PARTICLES ARE CLOSEST TOGETHER IN A SOLID. Reflected sound is called an ECHO. HARD surfaces are best at reflecting sound. The LOUDER a sound, the MORE ENERGY it has. The dB SCALE measures HOW LOUD a sound is. A NOISE is any UNWANTED SOUND. Noise can cause HEADACHES, NAUSEA and VOMITTING. You can reduce the effects of noise by using DOUBLE GLAZING, EAR PROTECTORS or PUTTING NOISY MACHINERY IN SEPARATE ROOMS.

Revision Summary 2 The NUMBER OF VIBRATIONS EVERY SECOND is called the FREQUENCY of a sound. Frequency is measured in HERTZ. PITCH is the musical equivalent of frequency. HUMANS can hear up to a frequency of 20 000Hz. An OSCILLOSCOPE can be used to view sounds. The Ear-