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Talking on Mars

Waves, sound and light · level 4, lesson 6 of 6

A question to start

Imagine two astronauts on Mars, each with a speaker on the outside of their helmet. One plays a recording of their voice. What would the other hear?

The idea

Put together what you have learned:

  1. Quieter. The speaker sends about 20 dB less sound energy into Mars air: a hundredth as much.
  2. Muffled. The high parts of speech, which make sounds like "s", "t" and "k" clear, fade quickly in Mars air.
  3. Slower. The sound takes longer to arrive: at 240 m/s instead of 340 m/s.
  4. The same pitch. The frequency is set by the speaker, so the voice would not sound higher or lower.

So a voice would sound faint and muffled, and hard to understand beyond a short distance. Astronauts would talk by radio instead.

A voice played from a speaker, 5 m away Mars Earth
How loud about 20 dB quieter normal
High parts like "s" and "t" fade fast clear
Time to arrive 0.021 s 0.015 s
Pitch the same the same
radio: clearsound: faint, muffled

Inside a habitat, with air at a pressure like Earth's, voices would sound normal again.

Worked examples

1. Arrival time on Mars. \(5/240 = 0.021\) s.

2. On Earth. \(5/340 = 0.015\) s.

3. Pitch. A voice at 200 Hz stays at 200 Hz; the air does not change the frequency of a wave passing through it.

Try it

  1. Give three ways a voice would sound different in Mars air.
  2. Why would the pitch of the voice not change?
  3. Why would words be hard to understand at a distance?
  4. How would astronauts on Mars really talk to each other outside?
Answers
  1. Any three: quieter, muffled, slower to arrive.
  2. The frequency is set by the vibrating source, not the air.
  3. The high parts of speech, which make words clear, fade quickly.
  4. By radio.

Common mistake

"Voices on Mars would sound squeaky or deep." Pitch depends on the frequency of the source, which the air does not change. Voices would be quieter and muffled, not higher or lower.

Where it leads