BUY THE YEAR 9 PHYSICS WORKBOOK

## Transmission, Reflection and Absorption of Sound

• Similar to a light wave, when a sound wave encounters an object, one of three things can happen:
1. Transmission – the sound wave travels through the object.
2. Reflection – the sound wave bounces off the object, often creating an echo.
3. Absorption – the sound wave is ‘trapped’ by the object, where its energy is transformed into a small amount of heat.
• Usually a combination of all three processes occurs, with the proportion of each depending on the composition of the object and the frequency of the sound wave.
Hard surfaces reflect sound more than soft surfaces.
Thicker or more dense objects absorb more sound; thinner or less dense objects transmit more sound.
Low frequency sounds are more likely to be transmitted; high frequency sounds are more likely to be reflected or absorbed.
Example 1
When sound hits a brick wall:
• Most sound is reflected off the wall, while some sound is transmitted through the wall and some sound is absorbed by the wall.
• Higher frequencies are more likely to be reflected, while lower frequencies are more likely to be transmitted or absorbed.
Example 2
When sound hits a cushion:
• Most sound is transmitted through the cushion, while some sound is absorbed by the cushion; very little sound is reflected off the cushion.
• Higher frequencies are more likely to be absorbed, while lower frequencies are more likely to be transmitted.

When encountering an object, sound waves may be transmitted, reflected or absorbed.

(Header image: Thaut Images, Adobe Stock)