Sound Demonstrations Sound waves are caused by vibrations and carry energy through a medium
What is a sound wave? • BrainPop password and login mcbrayer
Humans hear sounds waves in a limited frequency range • From 20 vibrations per second (20 Hertz) to 20,000 vibrations per second (20,000 Hertz) • The number of vibrations that are produced per second is called frequency. • Frequency varies for each sound and is measured in hertz. One hertz is equal to one vibration per second.
How does frequency affect pitch? • A sound with a low frequency will have a low pitch, such as a human's heartbeat. • A sound with a high frequency will have a high pitch, such as a dog whistle. • Sounds below the range of human hearing is Infrasound. • Sounds with a frequency above the range of human hearing is Ultrasound.
How do we measure sound? • Sound meter and oscilloscope (A device for viewing oscillations, as an electrical voltage or current, by a display on the screen.) • Use Microphone and applets on computer. • Test Your Hearing range – It is best to use headphones and be in a quiet room.
How will your hearing range change? • The hearing range of humans gets worse with age. People lose the ability to hear sounds of high frequency as they get older. • The highest frequency that a normal middle-aged adult can hear is only 12-14 kilohertz. • Also, the hearing range for men worsens more quickly than the hearing range for women. • This means that women will have the ability to hear notes of higher pitch than men of the same age do.
Loudness is measured in decibels (dB) • Amplitude = Loudness • We hear pressure (the amplitude) of sound as loudness. It takes more energy to create a louder sound. Too loud of a sound can cause deafness.
Amplitude • The bigger the difference in the amplitude of the wave the louder the sound.
Pitch – a measure of how high or low a sound is and depends on frequency • Penny Whistle - show how works. • Homemade Penny whistle (need straws and scissors) • Make and then cut to change pitch • Make and add a hole at the end • How is the sound made? • Have you ever held a blade of grass between you thumbs and made it “sing”? How does cupping your hands around the blade help the sound? • Boom Wackers • Without the cap – Whack two different tubes against your upper leg. Compare tubes of different lengths. • Which tube produced a lower tone? • Why do you think the longer tubes produced lower tones? • Cap one end of the tube and whack again. • How does the tone of the caped tube compare to the open tube? • Strike a 288 Hz tuning fork and hold it just on the inside end of the tube • How does wavelength affect pitch? • The longer the wavelength the lower the pitch.
Mechanical waves need a medium • Clock in a vacuum Medium affects the speed of the wave • Oven racks (vibrations, pitch and frequency) • Can telephone
Speed of sound • In Air (0 degrees C) = 331 m/s • In Air (100 degrees C) = 386 m/s • Oxygen = (0 degrees C) = 317 m/s • In Water = 1,490 m/s • Copper = 3,813 m/s • Rubber = 54 m/s
Tuning forks • Tuning forks – touch to water in glass, touch to different materials how does that affect the sound/vibrations? • The wavelength of the sound that the tuning fork emits is much larger than the width of the tuning fork’s tines. As a result, air has plenty of time to move around the tines during each cycle of vibration. • Thus, instead of pushing air toward and away from your ear as it vibrates, each tine prevents the air from flowing around it and helps the tine push the air toward and away from your ear. You hear much more sound as a result.
Waves and Vibrations • Thunder Drum- The vibrating spring causes the drumhead to vibrate, which in turn causes the air inside the drum to vibrate. The air in the drum begins to resonate, and the volume of the sound increases. • Resonance – a phenomenon that occurs when two objects naturally vibrate at the same frequency. • For example, when both the guitar body and the string are vibrating at the same frequency. The guitar body has a larger area than the string and is in contact with more molecules in the air. So the body is a better at transferring the vibrations to the air than the string is. • Breaking of a wine glass • Tacoma Bridge collapse • How does this relate to the Thunder Drum?
Waves and Vibrations • The natural frequency of an object depends on the object’s shape, size, mass, and the material from which the object is made • Talking Cups • Telephone cans – • How is sound transferred from one can to the other? • What is the medium that it is being transferred in? • Sound waves are what type of wave? • Wine glasses with water – Your finger slides and sticks. Bowing the wineglass much the same way a violinist bows a violin string. With each cycle of vibration you add a bit of energy. • Which glass has the highest pitch? Did it have more or less water in it? • What do you believe caused the sound, the water, the air, or the glass? • How could you set up a musical scale?
Wavesand Vibrations • Glass bottles with water (Jacob) • Gently strike the side of the bottle with a metal spoon. Please note which bottle has the highest pitch and which has the lowest. • What vibrated to make the sound you heard? • Where did you hit the jar to give the best sound? • What is your hypothesis which bottle will have a higher pitch and which will have a lower pitch. • What did you find out?
Naturalfrequency • Singing Rod • Just like the wine glasses, guitar, singing cups, thunder drum the singing rod has a natural frequency its particles want to vibrate at when energy is introduced. • By holding the rod at the node (the place where the object is not moving) and vibrating the antinode the natural frequencies of vibration can be achieved. • Touching a node will not dampen the sound; touching an antinode will.
Harmonic Vibrations • Plastic swing tube • Twirl above head • Increase the speed of the tube • Change the direction you spin the tube • Change the end of the tube you are holding and do all of the above steps again. • Choose the end that worked the best and try lifting the tube up and down when you spin it • What did it sound like? What type of sound did it make? • Did the sound change when you increased the speed? What did it sound like? • Did changing the direction change the sound? • Did changing the direction of the tube change the sound? • Write a statement explaining how best to get sound from the tubes. • How does the speed of the tube affect pitch? • The air a the tube ends flows inward and outward together and the air at the middle of the tube experiences up and down pressure fluctuations, but no velocity fluctuations. • The higher the tones the more places in the tube that are experiencing up and down pressure fluctuations.
Standing Waves • Carpet Tubes • What happens to the air in the tube as it is lowered over the flame? • What happens to the pitch when the size of the tube changes? • This is really the principle used by any wind instruments in a band or orchestra. The instrument has a hollow tube of some sort, its length will determine which frequencies it will amplify and its shape will determine the quality or type of sound it will give out. The musician produces a vibration, usually with the lips or a reed, and the air in the hollow tube will vibrate in resonance with whatever frequency it is designed to amplify.
Standing Wave • Guitar or Violin String • Pressing down on the string creates a node at that point. • The location of the node determines the pitch of the note.
Interference • When several waves are in the same location, they combine to produce a single, new wave that is different from the original wave. • Constructive Interference increases the amplitude. • Destructive interference decreases amplitude.
Tuning forks • Strike the prongs of a large tuning fork with your rubber heal. Observe the loudness of the sound and use a stopwatch to measure the length of time it can be heard before it dies away. What was the relative loudness of the tuning fork, was it loud or could you barely hear it? How long does it take for the sound to die out so you can no longer hear the tuning fork? • Strike the fork again. This time hold the rod end firmly against a tabletop. Observe the loudness of the sound and time the length of time it can be heard. • What is the relative loudness now, was it loud or could you barely hear it? • How long does it take for the sound to die out so you can no longer hear the tuning fork? • What happens when the tuning fork is placed near water? • Which would spill the water the most a small tuning fork or a large tuning fork? • Why?
Gas Bottles with water and Tuning Fork • Each time the tuning fork is held above the glass bottles you are actually hearing 2 sounds, not one. • You are hearing the sound made by the tuning fork and the sound that reflects off the water and reemerges from the jar. • When the reflected wave reemerges, it overlaps with the wave coming from the tuning fork. • If the wave emerging from the jar overlaps constructively you will hear a loud sound. • If the emerging wave overlaps destructively, you will hear no sound or a very low amplitude sound. • How does this demo also relate to Resonance?
Doppler Effect • Motion between the source of waves and the observer creates a change in observed frequency. • Frequency changes the Pitch • Examples • Ambulance • Doppler ball • Doppler Radar – Radar dome receives radio waves that have been sent out an then reflected back by rain, snow, and hail. Meterorologist observe frequency shifts. Do you remember learning about the Doppler Shift in space science?