2. THE NATURE OF SOUND WAVES Sound is a form of energy propagated as waves that make our eardrums vibrate. Sound waves are longitudinal waves which is required a medium for its propagation. Sounds are produces by vibrations such as the vibrations of the coneshaped diaphragm of loudspeaker, guitar strings, column of air in a musical instrument a tuning fork Sound waves cannot travel in a vacuum because there is no medium(particles) through which the sound energy can be propagated. 3. How is sound produced by a vibrating objects? When a tuning fork vibrates, layers of air vibrate and the sound energy is propagated through the air around it in the form of waves. When the tuning fork moves forwards, the air is compressed. When the tuning fork moves backwards, the air layers are pulled apart and cause a rarefaction. Therefore, a series of compression and rarefactions will produce sound. 4. Why does sound waves is a longitudinal waves? The air particles vibrate backward and forward in the direction parallel to the direction of propagation of the sound wave. Wavelength of sound, = the distance between two successive regions of compression or two successive regions of rarefaction. 5. SPEED OF SOUNDSound waves travel faster in solid > liquid > gas 6. LOUDNESS & AMPLITUDE OF SOUND The loudness of a sound is considered to be high or otherwise depending on the hearing ability of a person. Loudness is influenced by the amplitude of the sound wave. 7. PITCH & FREQUENCY OF SOUND The pitch of a sound or a musical note is an indication of how high or low the sound is. The pitch of a sound is determined by its frequency : a high pitch corresponds to a high frequency. 8. A P P L I C AT I O N S O F S O U N D WAV E S Cleaning with Ultrasonic Waves - Dentist use ultrasonic waves to removes plaque from teeth Locating an object under water - SONAR is a system used to detect underwater objects or to determine the depth of the water by mean of an echo. - Ultrasound signal is sent out from a transmitter. - Its echo from the seabed is detected by a receiver which is connected to an electrical recording circuit. - The time interval, t between the sending and receiving of the ultrasound signal after reflection from the seabed is measured. 9. Disintegration of kidney stones - sound waves of high energy are directed at the kidney stones to destroy them in the cavity of the kidney. A bat can navigate in darkness When ultrasonic waves emitted by the bat hit an object, they are reflected back and received by the bat. The time between the emission of the sound waves and reception of the reflected waves enables the bat to estimate the position of the object accurately. This enables the bat to adjust its direction to avoid knocking at the object. 10. CALCULATING DISTANCES USING THE REFLECTION OF SOUND WAVES 11. EXAMPLE 1. a student is standing at a distance of 45 m from a wall. He gives loud clap and the echois heard after 0.3 s, calculate the speed of sound in air. 12. An ultrasonic wave is used to determine the depth of a seabed. A pulse of ultrasound is generated and travels to the seabed and reflected by it. The time taken by a pulse of ultrasonic wave to travel to and fro the seabed is 0.28 s. It the speed of sound in the water is 1 500 ms-1, calculate the depth of the seabed.