Physics·Properties of waves · NSSCO 4.4
Sound
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Sound is all around you, and it always starts the same way — with something vibrating. In this lesson we watch a vibration turn into a longitudinal wave of compressions and rarefactions, discover why sound needs a medium and cannot cross a vacuum, learn how fast it travels in air, water and steel, connect pitch to frequency and loudness to amplitude, find the range of sounds a healthy ear can hear, and finish with echoes — using v = 2d/t to measure the speed of sound, plus the clever ways humans and animals use ultrasound.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 4.4):
- Describe how sound is produced by vibrating sources, travels through the air, and is received by the ear
- Explain that sound is a longitudinal wave and that a medium (solid, liquid or gas) is needed — there is no sound in a vacuum
- State that the speed of sound in air is about 330–340 m/s, and that sound travels faster in liquids and faster still in solids
- Relate the pitch of a sound to its frequency, and the loudness of a sound to its amplitude
- Describe the waveforms of sounds displayed on an oscilloscope
- Suggest the audible range of a healthy human ear (about 20 Hz to 20 000 Hz) and discuss the effect of loud noise on hearing
- Describe how echoes are produced and measure the speed of sound in air from an echo using v = 2d ÷ t
- Discuss how humans and animals use echoes, and describe uses of ultrasound
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