Sound
Physics · ध्वनि · 22 facts
Sound: longitudinal mechanical wave; needs medium
Cannot travel through vacuum; no sound in space
Speed: solids > liquids > gases
Air=343m/s(20C); water=1500m/s; steel=5100m/s
Frequency: vibrations/second; unit=Hertz(Hz)
Human audible range: 20Hz to 20000Hz
Infrasound <20Hz; Ultrasound >20000Hz
Ultrasound: SONAR, sonography, cleaning, echocardiography
SONAR: Sound Navigation And Ranging; sea depth, submarines
Echo: sound reflection; min distance 17.2m in air(20C)
Pitch depends on frequency; Loudness on amplitude(dB)
Conversation=60dB; whisper=20dB; pain=120dB; jet=140dB
Doppler Effect: freq changes when source/observer moves
Ambulance siren: higher approaching, lower moving away
Sonic boom: shock wave when object exceeds sound speed
Mach number = object speed/sound speed; Mach1=sound speed
Noise >80dB harmful; hearing loss, stress
Bats, dolphins use echolocation (ultrasound)
Resonance: external freq=natural freq causes max vibration
Lightning seen before thunder: light faster than sound
Quality/Timbre: distinguishes same note on different instruments
Sound speed increases with temperature of medium