Task 1: SOUND THROUGH SOLIDS, LIQUIDS AND GASES
In the previous lesson you have learned that sound travels in solids, liquids and gases…and it travels with a different speed. Sound is fastest in a solid and more slow in a gas. Watch this video about sound travelling in solids, liquids and gases and learn why does sound travel with a different speed.

Task 2: SOUND AND PARTICLES
Revisit lessons related to year 7 unit Understanding Matter. Here you have learned that all matter is made up of particles. Think about linking the fact that all matter is made up of particles and sound moving through solids, liquids and gases with different speeds.

The above video has shown that sound travels faster in solids because here the particles are very close together. On the other hand, the speed of sound is slower in gases because here the particles are far from each other. So the closer the particles are, the fastest is the speed of sound. A sound wave passes through air because the vibrating particles bump into their neighbours. These particles pass the vibration energy and the sound wave moves on.

Task 3: SOUND IN A VACUUM

Do you think that you can hear sounds in space? That is, can sound travel through a vacuum?
From Task 2 you should know the answer. In a vacuum there are no particles. Therefore sound cannot travel through a vacuum. We can demonstrate this as shown in Resource 1_BELL JAR EXPERIMENT by using a bell jar, a bell and a vacuum pump. Follow this video and observe what happens.

The same experiment is shown again in this video. The scientist measures the sound levels through a sound meter.

You may download Resource 2 and 3_SOUND THROUGH DIFFERENT MEDIA. These shows a good summary of the last two lessons.