Year 7 Science · Unit 3 · Lesson 16
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Learning Goals
Read the graph — Speed of Sound in Different Materials
Study the bar graph below, then answer the questions.
Data: Nave, C.R. (2019). HyperPhysics — Speed of Sound. Georgia State University.
(a) Describe the overall trend shown in the graph — how does the speed of sound change from air to steel?
(b) Predict: would sound travel faster through bone or through water? Explain your reasoning using the graph as evidence.
(c) Use a scientific idea from the lesson to explain WHY sound travels so much faster in steel than in air.
Real-world context
In 2023, researchers from the Australian Institute of Marine Science used SOSUS-style underwater hydrophones in the Indian Ocean to track blue whale calls across thousands of kilometres. Submarines operating in the region also communicate via low-frequency acoustic signals rather than radio waves. Unlike light or radio waves, which are heavily absorbed by seawater, sound travels efficiently through the ocean — particularly at a depth known as the SOFAR channel (~600–1200 m), where sound is "trapped" and can travel enormous distances with little energy loss.
(a) Using what you know about sound and mediums, explain why sound is a better way to communicate underwater than light or radio waves.
(b) Blue whale calls have a frequency of about 10–40 Hz. Would a human diver be able to hear these calls directly? Use the term "hearing range" in your answer.
1. A ship's SONAR sends a pulse and receives the echo 6 seconds later. Sound travels at 1480 m/s in water. Calculate the depth of the ocean floor directly below. Show your working.
2. A student claps near a cliff and hears the echo after 2 seconds. If the speed of sound in air is 340 m/s, how far away is the cliff? Explain why you divide by 2.
Wrap Up
In one sentence, what was the main idea of this lesson?