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Sound Waves Worksheet

Class 8 & 9 Science · about 35 minutes · open the simulation at jugnix.com/simulations/sound-waves

NameClassDate

By the end you will: relate frequency, wavelength and speed, compare sound in different materials, and solve echo problems.

A. Explore with the simulation

  1. Pick the 🎵 A note (440 Hz). Choose each material and record the speed and the wavelength.

    MaterialSpeed (m/s)Wavelength
    Air
    Water
    Steel
    Space (vacuum)

  2. In air, move the frequency from 🥁 Drum (60 Hz) to 🪈 Flute (1000 Hz). What happens to the wavelength? To the pitch?

  3. Change the loudness. What changes in the wave: its frequency, its wavelength or its amplitude?

  4. Pick the 🦇 Bat call (40,000 Hz). Who can hear it? What is this kind of sound called?

B. Calculate (then check in the simulation)

  1. A sound wave in air (343 m/s) has a wavelength of 0.5 m. Find its frequency and time period.

  2. A boy shouts towards a cliff and hears the echo 3 s later. How far away is the cliff? (Speed of sound 343 m/s)

  3. A ship's sonar sends a pulse down and gets the echo from the sea bed 2 s later. Sound in sea water travels at 1500 m/s. How deep is the sea?

  4. Why do we see lightning before we hear thunder? A storm's thunder arrives 5 s after the flash: about how far away is it?

C. Think it through

  1. Why can you hear a train coming sooner by putting your ear to the rail (don't try it!) than through the air?

Answer key (for teachers and parents)

  1. Air: 343 m/s, 0.78 m · Water: 1480 m/s, 3.36 m · Steel: 5960 m/s, 13.5 m · Vacuum: 0 m/s, no wave: sound needs particles to travel.
  2. The wavelength gets shorter (5.7 m to 0.34 m) and the pitch gets higher. Frequency × wavelength stays 343 m/s.
  3. Only the amplitude (the height of the wave). Loudness depends on amplitude; pitch depends on frequency.
  4. The dog, the cat and the bat, but not people or elephants. Sound above 20,000 Hz is ultrasound.
  5. f = v ÷ λ = 343 ÷ 0.5 = 686 Hz. T = 1 ÷ f = 1 ÷ 686 ≈ 0.0015 s (1.5 ms).
  6. Sound goes there and back: total 343 × 3 = 1029 m, so the cliff is 1029 ÷ 2 ≈ 515 m away.
  7. Depth = 1500 × 2 ÷ 2 = 1500 m.
  8. Light (3 × 10⁸ m/s) is almost a million times faster than sound. Distance ≈ 343 × 5 ≈ 1.7 km.
  9. Sound travels about 17 times faster in steel (5960 m/s) than in air (343 m/s), and it loses less energy along the rail.

Free to print and share for teaching. Made with the interactive simulation at jugnix.com/simulations/sound-waves.