1. © Oxford University Press 2011 IP1.29.3 Sounds around us Sounds around us

2. © Oxford University Press 2011 IP1.29.3 Sounds around us Introduction to sound waves  Sound waves are longitudinal waves.  Sound waves are created whenever an object vibrates.  Sound waves can travel through all solids, liquids and gases.  The denser the material the sound travels through, the faster it travels.  Sound can’t travel through a vacuum. There are no particles in the vacuum to vibrate.

3. © Oxford University Press 2011 IP1.29.3 Sounds around us Speakers vibrate in and out when they receive an electric current. These vibrations create the sound.

4. © Oxford University Press 2011 IP1.29.3 Sounds around us A musical instrument often has a string, a column of air or a reed. This causes vibration that creates sound waves.

5. © Oxford University Press 2011 IP1.29.3 Sounds around us A tuning fork delivers an exact pitch which depends on the length of its two prongs. If you put a tuning fork in a glass of water you can confirm that sound is caused by vibrations.

6. © Oxford University Press 2011 IP1.29.3 Sounds around us Ultrasound has a frequency too high for the human ear to detect. It is mostly commonly used for medical imaging.

7. © Oxford University Press 2011 IP1.29.3 Sounds around us If a note of the correct frequency is played for long enough it will cause a glass to vibrate and eventually break.

8. © Oxford University Press 2011 IP1.29.3 Sounds around us Sound waves and the human body  When you talk, your vocal chords vibrate. You can feel them if you gently press the front of your throat whilst talking.  When vibrations reach our ear, they make our eardrum vibrate and we detect this as a sound.  Humans can hear sounds up to a frequency of 20 000 Hz. Sound waves above this frequency are called ultrasound.  As you get older you lose your ability to hear high frequency sounds. By the time you are twenty you will only be able to hear 16 000 Hz; this falls to 13 000 Hz at thirty.  Listening to music that is too loud does permanent damage to your hearing.