Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define sound and how it is produced by vibrations.
• Describe the longitudinal wave nature of sound.
• Explain how sound travels through different media.
• Describe the structure and function of the human ear.
• Define pitch and loudness and relate them to frequency and amplitude.

Lesson summary

Sound is everywhere! From the vibrant music of Gqom and Amapiano booming from taxis in Durban to the chirping of crickets on a farm in Limpopo, sound plays a vital role in our daily experiences. Understanding sound and how we hear is crucial not only for appreciating the world around us but also for protecting our hearing, especially in a country where noise pollution can be a significant issue in densely populated areas. Think about the sounds in a busy marketplace, a construction site, or even at a school sports event. All these sounds can impact our hearing health.

Lesson notes

What is Sound? Sound is a form of energy that travels in waves. It is produced when something vibrates. These vibrations create disturbances in the surrounding medium (usually air, but it can also be a solid or liquid), and these disturbances travel as waves to our ears, which then interpret them as sound. Think about hitting a drum. The drum skin vibrates, pushing and pulling on the air around it, creating sound waves.

Sound Waves: Longitudinal Waves Sound waves are longitudinal waves. This means that the particles of the medium (air, water, etc.) vibrate parallel to the direction the wave is travelling. This is different from transverse waves, like light waves, where the particles vibrate perpendicular to the direction the wave is travelling. Imagine a slinky. If you push and pull one end of the slinky, you'll create areas where the coils are compressed together (compressions) and areas where they are spread apart (rarefactions). Sound waves are similar, with: Compressions: Regions of high pressure where the air particles are squeezed together.

Rarefactions: Regions of low pressure where the air particles are spread apart. A complete sound wave consists of one compression and one rarefaction. How Sound Travels Sound needs a medium to travel through. It cannot travel through a vacuum (like space) because there are no particles to vibrate.

Solids: Sound travels fastest in solids because the particles are close together, allowing vibrations to pass quickly.

Liquids: Sound travels slower in liquids than in solids but faster than in gases.

Gases: Sound travels slowest in gases because the particles are far apart. The speed of sound in air at room temperature (around 25°C) is approximately 343 meters per second (m/s).