Sound is a form of energy that is produced by vibrating sources placed in a medium like solids, liquids, or gases. It travels as a longitudinal wave and can be transmitted through any medium whose particles can vibrate, with solids transmitting sound the fastest. The speed of sound is affected by temperature and humidity but not pressure. It can be measured directly by having two observers time the delay between a sound and its perception. The human ear can detect sounds between 20 Hz and 20 kHz with anything higher or lower being considered ultrasound or infrasound, respectively. Ultrasound has medical imaging applications while echoes and reverberations are used for detection purposes by various organisms and technologies. Pitch and loudness describe frequency and amplitude of sound

1. SOUND SECONDARY 3 PHYSICS

2. NATURE AND PRODUCTION OF SOUND Sound is….. A form of energy an example of longitudinal wave Produced by vibrating sources placed in a medium. (solid, liquid or gas)

3. The medium of Transmission Any medium that has particles that can vibrate will transmit sound. Solids can transmit sound fastest followed by liquid then air. Application: In olden days, people would hear the ground for movement.

4. Effect of Physical Conditions Temperature? Sound travels faster in higher temperatures Humidity? Sound travels faster in high humidity Pressure? Pressure has no effect on speed of sound

5. Determining the Speed of Sound Using Direct Method Observers A and B are positioned at a known distance, s, apart in an open field. Observer A fires a starting pistol. Observer B starts the stopwatch on seeing the flash of the pistol and stops the stopwatch when he hears the sound. The time interval, t, is then recorded. Speed of sound = s/t Repeat the experiment to minimise random errors. A and B exchange positions to cancel the effect of wind on the speed of sound and repeat a few times again.

6. Audible Frequencies The human ear can only hear sounds of frequencies between 20 Hz and 20 kHz. Any sound with frequency higher than 20 kHz is known as ultrasound . Any sound with frequency lower than 20 Hz is known as infrasound .

7. Application of Ultrasound In medical diagnosis Used to obtain images of internal parts of the body. Commonly used in pre-natal examination.

8. Reflection of Sound Formation of Echoes When sound hits a hard surface, it will “bounce” off the surface. The sound that is reflected back to us is called an echo.

9. Reverberations It is the prolonged sound due to the merging of many echoes. The many echoes are produced because sound will be reflected off the different walls in a room. Reflection of Sound

10. Uses of Echoes Fishing boats use echoes to detect shoals of fish Measurement of the depth of the ocean War ships use echoes to detect mines Some animals use echoes to detect obstacles. Eg bats

11. Pitch When describing a musical note as ‘high’ or ‘low’, we are actually talking about the pitch of the sound. Frequency affects pitch. High frequency – high pitch Lower frequency – lower pitch Shorter strings or air tunnels have higher frequency.

12. Loudness It is the volume of a sound. Loudness depends on the amplitude of the sound wave. Louder sounds have larger amplitudes and vice versa. It is measured in decibels (dB).