Speed of sound Sound barrier Frequency Amplitude Pitch
Loudness Decibels
Sound insulation
Download a free sound-level meter. Use this meter to investigate the effect of changing the thickness of a material of your choice on the level of sound insulation that material provides.
Learning Intentions
In this topic we are learning to: z Compare the speed of sound with the speed of light. z Examine the factors that affect the pitch and loudness of a sound. z Explore the importance of sound safety.
Sound is a form of energy that is transferred in waves.
To produce sound, we need to make something vibrate. For example, by plucking the strings of a guitar or vocal chords vibrating in our throats.
How Do We Hear?
1. When an object produces sound, it causes vibrations in the air molecules around it.
Fig. 19.4.1 Sound is produced by vibrations
2. These vibrations produce a sound wave. 3. This wave passes through the air and makes the eardrum vibrate.
Fig. 19.4.2 Sound vibrating an eardrum
Sound needs a medium to travel through. Without a medium, there would be nothing to pass on the sound waves.
Particles and sound
A student holds a clothes hanger from two pieces of string as shown in Fig. 19.4.3.
1. Their lab partner strikes the hanger gently with a wooden stick. Explain why a loud sound is not heard.
2. The student then puts the fingers holding the hanger in his ears. The hanger was again struck with the wood. Predict what happens to the loudness of the sound.
3. Try this out in class and discuss your findings with your lab partner.
