Transcript Sound
Sound Do you hear what I hear? The Facts Sound … 1. Energy produced & transmitted by vibrating matter 2. Travels in waves - longitudinal 3. Travels more quickly through solids than liquids or gases Why is Sound Longitudinal? Waves in air can’t really be transverse, because the atoms/molecules are not bound to each other fancy way of saying this: gases can’t support shear loads Air molecules can really only bump into one another Imagine people in a crowded train station with hands in pockets pushing into crowd would send a wave of compression into the crowd in the direction of push (longitudinal) jerking people back and forth (sideways, over several meters) would not spread into the crowd but if everyone held hands (bonds), this transverse motion would spread into crowd The Ear Sound is carried to our ears through vibrating air molecules. Our ears take in sound waves & turns them into signals that go to our brains. Middle Ear Vibration - Back and forth movement of molecules of matter - For example, Compression - Where molecules are being pressed together as the sound waves move through matter - For example, - a wave travels through the springs just like sound waves travel through the air the places where the springs are close together are like compressions in the air. Sound Waves - ALL sound is carried through matter as sound waves Sound waves move out in ALL directions from a vibrating object Remember Frequency? Frequency is the number of waves moving past a point in one second Pitch A measure of how high or low a sound is Pitch depends on the frequency of a sound wave For example, - Low pitch - High pitch - Low frequency - High frequency - Longer wavelength - Shorter wavelength Sound and Instruments - - - - Instruments can be played at different pitches by changing lengths of different parts. For example, Another way to make different pitches is to change the thickness of the material that vibrates. For example, A trombone’s mute absorbs some of the sound waves produced, thus producing a softer note when played. SO: ONE WAY TO CHANGE PITCH IS TO ADD MORE MATTER (LENGTH, THICKNESS, ETC.) This works because there is more material so it vibrates more slowly and the wavelengths are longer = lower frequency. Is there another way? Yes: Another way to change frequency is to change the space for the vibration. EXAMPLE: glass bottles with different amounts of liquid The compressions are either pushed close together (high frequency) or have room to stretch out (low frequency). Let’s Review! You can change PITCH (high/low notes) by changing two things: One = the amount of matter Two = the air space What about AMPLITUDE???? (loudness)??????? Amplitude changes when force changes the amount of matter in the compression. How could you do that? (blow harder, strike harder, etc.) Sound Familiar? The Physics of Sound The Physics of Sound Healthy Cochlea The cilia ( sensory hairs) appear normal Damaged Cochlea Loss of cilia as a result of Noise Hearing Protection Devices and Their Noise Reduction Ratings EAR Foam Plugs (NRR = 29 dB) EAR CARBOFLEX (NRR= 20 dB) Moldex PURAFIT Foam Plugs (NRR=30 dB) What IS the Speed of Sound? Carried through air at 345 m/s (770 m.p.h) as compressions and rarefactions in air pressure Example Sound Speeds Medium sound speed (m/s) air (20C) 343 water 1497 gold 3240 brick 3650 wood 3800–4600 glass 5100 steel 5790 aluminum 6420 http://hypertextbook.com/physics/waves/sound/ Stationary Sound Wave Doppler Effect Breaking Sound Barrier Sonar - - An instrument that uses reflected sound waves to find underwater objects For example, Humans use sonar to locate or map objects Animals use sonar or echo location to find their prey; these sounds have such a high pitch or frequency that the human ear cannot hear Blue Man Group Challenge! Blue Man Group You’re HIRED! So what am I supposed to do exactly? I don’t know what to make… what do I do!?! Ugh. That’s tough, isn’t it? I recommend setting aside a little bit of brainstorming time first. That means you let your imagination run wild. Think of anything and everything that would be cool to make, and write it all down. There are no wrong answers in brainstorming. Just go crazy! Still stuck? Look around your house and neighborhood. Broken umbrella? Paper bag? Floss? Let yourself imagine how those could create music. Then gather some objects and start experimenting. Does anything make an interesting sound? Are you inspired yet? Can I use or make an instrument that already exists? No way! You could, if you really wanted to…but wouldn’t you rather challenge yourself to invent something never seen before? C’mon, I know you can do it! Besides, building a piano is really complicated. And putting a piece of string on top of a piano isn’t really groundbreaking, either. Let’s look at some examples! Instruments Awesome Not Awesome Shoe box with rubber bands attached Oatmeal box with beads in it or paper on top to create a drum Tambourines made from paper plates Bongos made from tubs and paper Etc How are you graded? Lets look at the rubric. What are some practical ways we use sound energy? The Human Ear Introduction Your ear converts sound waves into nerve impulses that your brain interprets. Parts if the Ear The Outer Ear Contains the pinna, ear canal and ear drum The Middle Ear Contains three bones: hammer, anvil & stirrup The Inner Ear Contains the cochlea and auditory nerve How it works – in a nut shell At the outer ear, sound waves are focused by the pinna down the ear canal to the eardrum. The sound waves make the eardrum vibrate. The vibrations are amplified by 3 middle ear bones, the hammer, anvil and stirrup. How it works The stirrup transfers the vibrations to the cochlea within the inner ear. The vibrations activate hair cells inside the cochlea, which send electrical signals to the brain along the auditory nerve. The brain interprets these signals as sound High vs. Low Sounds High pitch sound carry more energy and travel further into the cochlea Lower pitch sounds carry less energy and don’t travel as far into the cochlea Anatomy of the Human Ear Intensity and Loudness The intensity of a sound wave is the amount of energy the wave carries per second through a unit area. Loudness, or sound level, is measured in decibels (dB) Sound Loudness (dbs) Hearing Damage Average Home 40-50 Loud Music 90-100 After long exposure Rock Concert 115-120 Progressive Jet Engine 120-170 Pain Space shuttle engine 200 Immediate and irreversible Frequency Frequency is measured in Hertz (Hz) The frequency of a sound wave is the number of vibrations that occur per second Meaning, a frequency of 50 Hz means fifty vibrations per second. People hear sounds with frequencies between 20 HZ and 20,000Hz. Ultrasound sound waves with frequencies above the normal human range of hearing. - Infrasound - sounds with frequencies below the normal human range of hearing.