CBSE Book Class 8 Science Activity How Does Sound Travel

 SOUND

'Sound is produced by vibrating bodies. When you pluck a stretched rubber band, it makes sound,' read Dhwani from her physics book. 'How does this sound reach our ears?', wondered Dhwani. Her father who  was sitting nearby explained to her that the air molecules just next to the rubber band start vibrating.  These in turn pass the vibrations from one part to another. The air molecules themselves do not move  from the rubber band toyour ears. Come let me show you how that happens.

Flick the first card so that it falls on the next card. What do you see? Do you notice that the event of the first card tipping on the second card is repeated in sequence along the whole length of the cards? On tipping one card the impact travels until the very last card falls down. This is how a sound wave travels? The cards represent the molecules. They stay on at their positions but pass on the impact or pulse from one card to the other till the end. Dhwani was thrilled to see this. It was such fun to see the cards falling one by one. She then recalled how once Suniyo, her friend had flattened all the cycles placed in the cycle stand in their school. This  activity  raised  several  questions  in  Dhwani's  mind.  Will  sound  travel  through  vacuum?  How differently does it travel through solids than in gases? She had learnt in an earlier class that the molecules are tightly packed in solids as compared to gases. Since her scientist father seemed to have answers to all her questions, she went to him with all her  queries. He just told her to collect a few things. Come on, you too join Dhwani.

What to do: 

Tie a spoon in the middle of a piece of string about 50 cm long and hold it as shown in the first diagram. Ask a friend to hit gently the spoon with another spoon or a ruler. Listen carefully to the sound. The sound lasts for a while. Now hold the ends of the string in your ears. Look at the next picture to see how it is to be done. Ask your  friend to hit the spoon again with another one. Is the sound louder or feeble than before? How does the sound travel to your ears in the first case? What is the difference in the way sound now  travels when you hold the strings to your ears. 

Please refer to the link below - CBSE Class 8 Science Activity How Does Sound Travel