Transcript Sound
•Longitudinal wave •requires a medium (cannot travel in a vacuum such as space) is known as ACOUSTICS 2. What causes sound? • A sound is a vibration (rapid back and forth motion that creates a longitudinal wave – Remember this wave has compressions and rarefactions – The velocity of speed of sound depends on twos things:the medium it moves through and temperature Solid Liquid Gas •Fastest in solids, slowest in gases. Air = water= steel = •Supersonic: faster speed of sound. 340 m/s 1440 m/s 5000 m/s than the https://www.youtube.com/watch?v=gWGLA AYdbbc Can affect speed Do molecules move faster or slower as temperature increases? So would sound travel faster or slower as temperature increases? Speeds of Sound at T of 20 C • • • • • • • • Air Helium Hydrogen Water Sea water Iron/Steel Glass Aluminum • • • • • • • • 343 m/s 1005 m/s 1300 m/s 1440 m/s 1560 m/s ≈5000 m/s ≈ 4500 m/s ≈ 5100 m/s The highness or lowness of sound. •Depends on the frequency of sound waves. Everything has it’s own natural frequency High frequency = High pitch Low frequency = Low pitch Note: resonance (amplitude) is the strengthening of sound when combined with frequency •Also called LOUDNESS •Amount of energy •Depends on the amplitude of sound waves. (amplifier) Large Amp. = Loud sound Small Amp. = Soft sound Measurement of loudness Near total silence - 0 dB A whisper - 15 dB Normal conversation - 60 dB Lawnmower - 90 dB Threshold of pain - 120 dB A rock concert or a jet engine - 120 dB Gunshot, firecracker - 140 dB 8a. Normal hearing 20Hz--20 000 Hz 8b. Infrasonic sounds are below our hearing (below 20 Hz) 8c. Ultrasonic sounds are those above our hearing (above 20,000Hz) (ultrasound) 8d. Sound can damage hearing by damaging the fine hairs that vibrate •Sound waves reflecting from hard surfaces but spaced out so it is heard many times over long distances •Sound waves reflecting from hard surfaces but faster or closer together •Ex.: Multiple echo resulting from the direct sound AND the reflected sound Reverberation vs Echo Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com Sound is a pressure wave Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com Tuning fork creating a sound wave Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com Guitar String creating a sound wave Animations courtesy of Paul Hewitt and borrowed from physicsclassroom.com • Ultrasound can be used to create internal images of the human body – Ex. Pregnant woman gets a “picture” of her unborn baby • An equal mixture of all frequencies of sound • Used to calm stress • Used in office buildings • Yep! There is such a thing • Causes: – Damage to ear resulting in hearing loss – Stress • Caused by destructive interference • Result – hardly any or no sound • Bad for concert halls – designers be careful! use of sound waves to interpret echoes for location of landforms, prey, etc. by bats, dolphins, submarines (SONAR), etc. Change in pitch due to motion. https://i1.ytimg.com/vi/-wy5oX0AXv8/mqdefault.jpg Moving towards increases the pitch Moving away decreases the pitch