Physics · Grades 1–12

Waves & sound · Quick reference

Reference sheet for Grades 1 to 12: sound and vibrations and reasoning about waves. Sounds come from vibrations. Loudness depends on how big the vibrations are; pitch depends on how fast they are.

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Rule and key idea

Sound and vibrations

Sounds come from vibrations. Loudness depends on how big the vibrations are; pitch depends on how fast they are.

vibration → sound; bigger vibration → louder

A drum is tapped gently and then hit harder. What happens to the sound? → It gets louder.

Reasoning about waves

In a transverse wave the medium vibrates across the direction of travel; in a longitudinal wave it vibrates along it. In one medium the wave speed is fixed, so higher frequency means shorter wavelength.

v = fλ · same medium → same speed, so λ ∝ 1/f

A wave on a string has a wavelength of 4.8 m. The frequency is made 4 times larger while the wave speed stays the same. What is the new wavelength? → 1.2

Check yourself

Four practice questions on this topic. Try each one before you open the answer.

66 complete oscillations take 34 s. Find the period. Round to 3 decimal places if needed. Answer in s.
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0.515 s T = total time / number of cycles 34 / 66 = 0.515
An echo returns after 990 ms. The sound speed in this medium is 330 m/s. Find the distance to the stationary reflector. Round to 3 decimal places if needed. Answer in m.
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163.35 m d = vt/2 330 × (990/1000) / 2 = 163.35
14 complete oscillations take 41 s. Find the period. Round to 3 decimal places if needed. Answer in s.
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2.929 s T = total time / number of cycles 41 / 14 = 2.929
29 complete oscillations take 21 s. Find the period. Round to 3 decimal places if needed. Answer in s.
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0.724 s T = total time / number of cycles 21 / 29 = 0.724