Year 9 Science · Unit 4 · Lesson 6
Apply Worksheet
Learning Goals
Speed of sound in different media
The bar chart shows the speed of sound in four different materials. Study the chart, then answer the questions.
Data: typical values at 20°C. Source: Physics Education literature.
(a) Rank the four media from fastest to slowest for transmitting sound.
(b) Explain, using particle theory, why steel transmits sound approximately 15 times faster than air.
(c) A 440 Hz note is played. Calculate the wavelength of this sound in air (343 m/s) and in water (1,500 m/s). Show your working for both.
Real-world context
Humpback whales (Megaptera novaeangliae) migrate along the east coast of Australia and are known for their complex songs. Their vocalisations span a frequency range of about 20 Hz to 10,000 Hz and can travel thousands of kilometres through the ocean. Researchers from the University of Queensland have found that increasing ocean noise from shipping traffic — which includes low-frequency engine sounds of 100–500 Hz — disrupts whale communication.
(a) Sound travels approximately 1,500 m/s in seawater but only about 343 m/s in air. Using particle theory, explain why whale songs travel so much further in ocean water than the same sounds would travel in air.
(b) Humpback whales use a range of 20 Hz to 10,000 Hz. Explain, using your knowledge of frequency and pitch, why using this wide frequency range allows whales to communicate more effectively than using a single frequency.
(c) Explain why shipping engine noise (100–500 Hz) specifically disrupts whale communication. Use the concept of frequency overlap in your answer.
1. A sound wave travels through air at 343 m/s at 20°C. The temperature rises to 40°C. Predict what happens to the speed of sound, and explain why using the particle model of matter.
2. A medical ultrasound machine uses waves at 5,000,000 Hz (5 MHz) that travel at 1,540 m/s through tissue. Calculate the wavelength. Explain why a short wavelength is useful for detecting small structures inside the body.
Wrap Up
In one sentence, what was the main idea of this lesson?