Sounds and Circuits     (Worksheet 1)

Sounds
All sounds begin with an object that is vibrating. These vibrations travel away from the source. If these vibrations strike someone's eardrum, they may be heard.

Pitch and Frequency

Large objects vibrate slowly and produce only a few waves every second. These waves tend to have a low frequency and produce low-pitched sounds.  

 
Small objects vibrate quickly and produce lots of waves every second. These waves tend to have a high frequency and produce high-pitched sounds.  
     

The frequency of a wave is measured in hertz (Hz). An object which vibrates once every second and produces one complete wave every second has a frequency of 1 Hz.

Loudness
Objects that vibrate with large amplitudes produce loud sounds. Objects that have small vibrations produce quiet sounds.

Travelling Sound Waves
Sound waves travel by making particles vibrate. Sound can travel not just through air, but through all solids, liquids and gases. However sound cannot travel through a vacuum as there are no air particles present that can vibrate and transmit the sound.


Echoes
When sound waves strike a hard surface they are reflected. This reflected sound is called an echo. Ships use echoes to find the depth of the ocean beneath them. An echo sounder emits sound waves down towards the seabed. When the sound waves strike the seabed they are reflected back up towards the surface. A sound detector on board the ship listens for the echo. The deeper the sea the longer it takes for the echo to be heard.
Sound waves used in this way are called SONAR. This stands for Sound Navigation And Ranging.  Sonar can also be used by fishing boats to locate shoals of fish. If an echo is heard much sooner than expected this would suggest that fish were swimming beneath the boat and the sound waves have reflected back off the shoal of fish.

Hearing Range
An average human being can hear sounds that have a frequency higher than 20 Hz and lower than 20,000 Hz. This band of frequency is called our hearing range. (It is also sometimes called our audible range). Hearing or audible ranges do vary slightly from person to person. However our hearing range generally narrows, as we grow older.  Sounds that have a frequency too high to be heard by humans are called ultrasounds.
Other animals can hear ultrasounds. For example, dogs have a hearing range that extends to almost 40,000 Hz. Bats and Dolphins have hearing ranges that can extend well over 50,000 Hz.

Loudness and Decibels
BE AWARE! Constant exposure to loud sounds can damage your hearing. People that work in loud and noisy environments should wear ear protectors over their ears to avoid any damage to their ears. Loudness of sound is measured in decibels.

Sound Comprehension

1. How does all sound begin?
 		   Answer:________
2. How do large objects vibrate - slowly or quickly?
 		   Answer:________
3. What does a Hertz (Hz) measure?
 		   Answer:________
4. Do small vibrations produce loud or quiet sounds?
 		   Answer:________
5. What is an echo?
 		   Answer:________
6. What is the hearing range of a normal person?
 		   Answer:________
7. What is an ultrasound?
 		   Answer:________
8. Name two animals that can hear ultrasounds.
 		   Answer:________
9. What does SONAR stand for?
 		   Answer:________
10. How do we measure loudness?
 		   Answer:________