Sound
9th Grade Science · 6 lessons
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Lessons in this unit
- 1How Sound Is Produced and CarriedSound begins with something vibrating. The vibration pushes nearby particles together into compressions and lets them spread into rarefactions, and this pattern travels outwards. Without particles there is nothing to compress, so sound cannot cross a vacuum.Experiment
- 2Pitch, Loudness and the Oscilloscope TraceOn an oscilloscope, a higher-pitched note gives more cycles across the screen — higher frequency. A louder note gives a taller trace — greater amplitude. Pitch and loudness are independent: you can change one while holding the other steady.Experiment
- 3The Speed of Sound in Different MediaSound travels at roughly 340 m/s in air, about 1,500 m/s in water and around 5,000 m/s in steel. The closer and more strongly bound the particles, the faster the disturbance passes along — the opposite of the pattern for light.Experiment
- 4Echoes, Sonar and UltrasoundSound reflecting off a surface returns as an echo. Time it and you can find distance, because distance equals speed times half the round-trip time. Ships use this as sonar, and medicine uses ultrasound above 20 kHz to image inside the body without ionising radiation.Lesson
- 5The Human Ear and Hearing RangeThe pinna funnels sound to the eardrum, which vibrates. Three small bones amplify that motion into the cochlea, where hair cells convert it into nerve impulses. A healthy young person hears roughly 20 Hz to 20 kHz, and the upper limit falls with age and noise exposure.Experiment
- 6Noise, Damage and ProtectionSound intensity is measured in decibels on a logarithmic scale, so 90 dB carries ten times the intensity of 80 dB. Sustained exposure above about 85 dB damages hair cells permanently — they do not regrow, which is why hearing loss from noise is irreversible.Experiment
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