2Section 1 - The Nature of Sound Sound - a disturbance that travels through a medium as a longitudinal waveSounds are created by vibrations.Drum, guitar string, vocal cordsSound waves carry energy through medium (usually air)
3The Nature of Sound (con’t.) Sound waves reflect off objects, diffract through narrow openings and around barriers, and interfere with others.Reflection – when they hit a hard surface – Echo (harder and smoother)Diffraction - bending of sound waves around barriers. Can hear around corners, or sounds outside room with door openInterference – Constructive and destructive
4The Nature of Sound (con’t.) Speed of soundThe speed of sound depends on the elasticity, density, and temperature of the medium the sound travels through.air m/s 20oC)fresh water - 1,509 m/secLead – 1,210 m/sAluminum – 5,000 m/sElasticity - ability of a material to bounce back after being disturbed. Very elastic material , particles easily go back to their original positions, more elastic = faster.
5The Nature of Sound (con’t.) Density- how much matter, or mass, there is in a given amount of space or volume – denser=SlowerTemperature- warmer = fasterSpeed of sound in 20oC – 343 m/sSpeed of sound in 0oC – 330 m/s
6Section 2 - Properties of Sound Loudness – describes ones perception of the energy of a sound.The loudness of a sound depends on two factors: the amount of energy it takes to make the sound and the distance from the source of the sound.Larger amplitude of vibration - increase intensity
7Properties of Sound (con’t.) Intensity - the amount of energy the wave carries per second through a unit areaAs one moves away from a sound source, loudness decreases because intensity decreases. (pg 547)Loudness is measured in decibels (dB) Table pg. 548Each 10-dB increase in loudness represents a tenfold increase in the intensity of the sound.
8Properties of Sound (con’t.) Pitch - perception of the frequency of a sound – Low frequency = low pitchFrequency - number of vibrations that occur per secondHuman hearing range 20 Hz to 20,000 HzUltrasound - frequency above human rangeInfrasound - frequency below human rangeIn music, a pitch is a note.Larynx – (voice box) You change the pitch of your voice with your vocal cords.
9Properties of Sound (con’t.) Doppler effect - the apparent change in frequency as a wave source moves in relation to the listenerWhen a sound source moves, the frequency of the waves changes because of the motion of the source adds to the motion of the waves.
10Properties of Sound (con’t.) Sonic boom – the release of energy when sounds waves overlap (pg. 551) Sonic Boom Video
11Section 3 - MusicMusic - a set of notes (tones) that combine in patterns that are pleasingNoise - has no pleasing timbre and no identifiable pitchInterference occurs when two or more sound waves interact.The sound quality of musical instruments results from blending a fundamental tone with its overtones. Resonance also plays a role in the sound quality. (Timbre)
12Music (con’t) Fundamental Tones and Overtones- A standing wave can only occur at a specific frequencies that are called natural frequencies. Every object has its own natural frequency. Spring demoFundamental tone- The lowest natural frequency of an objectOvertones- The object’s higher natural frequenciesDiagram - fundamental frequency and overtones!!!!!!! (page 553)
13Music (con’t)Resonance – affects the sound quality of a musical instrument by increasing the loudness of certain overtones.Ex. Opera singer shatters crystal glass
14InstrumentsThere are three basic groups of musical instruments: stringed instruments, wind instruments, and percussion instruments.Stringed instruments - strings vibrate, length, thickness, material and tension of string effects frequency. Hollow body increases loudness through resonance.Wind Instruments - players lips vibrate against mouthpiece (reed) creating a vibration. Air column inside instrument vibrates. Length of air column adjusted with valves or slides determines note.
15InstrumentsPercussion Instruments - instruments vibrate when struck. Frequency effected by material used, size of instrument and tension of drum.
16Instruments (con’t.)Acoustics - The study of how sounds interact with each other and the environment.Constructive and destructive interferenceAuditorium designEar protection - destructive interferenceReverberation – Echos of a sound are heard after the sound source stops producing sound waves. Acoustics is used in the design of concert halls to control reverberation and interference.
17Instruments (con’t.)Beat - The regular changes in loudness of a sound when two sounds of different frequencies are played together. Piano tuner
18Section 4 - How you hear sound The outer ear funnels sound waves, the middle ear transmits the waves inward, and the inner ear converts the sound waves into a form that travels to your brain.Ear Diagram pg. 559Outer ear - ear canal, eardrumMiddle ear - hammer, anvil & stirrupinner ear - cochlea (cavity filled with liquid & 10,000 tiny hairs)
19How You Hear Sound (con’t.) Hearing loss caused by injury, infection, (birth defects,) and agingextended exposure to loud soundsHearing aids amplify sounds and can restore some hearing.
20Section 5 – Using SoundEcholocation - use of reflected sound waves to determine distances or to locate objectsSome animals, including bats and dolphins, use echolocation to navigate and to find food.Ultrasound technologies such as sonar and ultrasound imaging are used to observe things that cannot be seen directly.
21Using Sound (Con’t.)Sonar - a system of detecting reflected sound waves. (sound navigation and ranging)The sonar device measures the amount of time it takes to detect the reflected sound waves. The longer it takes to come back, the further away the object is. Using the speed of sound in the medium the distance is calculated. Calculation example.
22Using Sound (Con’t.) Uses of ultrasound & infrasound dog whistle - ultrasounddolphins & whales - echolocationbats - echolocationtoothbrushautomatic focus camera
23sonogram -ultrasound used to look inside human body to diagnose and treat medical conditions