What is sound? It is an external factor (stimulus) that affects the ear causing the sense of hearing. How is the sound produced? Sound is produced due to vibration.

Nature of sound waves Sound waves are mechanical waves needs a medium to propagate. Sound waves are longitudinal waves consists of compressions and rarefactions. Sound waves move in all directions surrounding the source of sound as spheres. G.R We hear sound from all directions that surround the sound source. Because the sound travels through air as pulses of compressions and rarefactions whose center is the sound source.

Sound velocity It is the distance which is covered by the sound waves in one second.

problems Sound waves are produced from a vibrating tuning fork of frequency 512 cycles/sec. if the wavelength of these waves is 60 cm. calculate the velocity of such waves through air. V = F x λ λ = 60 ÷ 100 = 0.6 m V= 512 x 0.6 = m/sec.

problems Calculate the wavelength of a sound wave propagating through sea water with velocity 1500 m/sec knowing that its frequency is 10 kilohertz. F = 10 x 10 3 = Hz. V = F X λ. λ= V = 1500 = 0.15 m F 10000

Properties of sound waves We can hear many and different sounds. These sounds may be: Pleasant to our ears such as music. Source of disturbance and irritation such as horns and loudspeakers. Source of fear such as the sound of strong winds and thunder.

Classification of sounds Musical tones: They are tones of uniform frequency and comfortable to be heard. Violin, piano, and reed pipe. Noise: It is sound of non-uniform frequency and uncomfortable to be heard. Drill, loudspeakers and horns of cars.

Sound pitch Sound intensity Sound quality The human ear can differentiate between the sound that reach it through three different factors:

Sound pitch It is a property by which the ear can distinguish between rough and sharp voices. Sounds is described as: High pitched soundLow pitched sound sharp/ softrough/ harsh as voice of womenas voice of men High frequencyLow frequency

Sound pitch Sound pitch depends on frequency. As sound pitch increases, frequency increases and vice versa. Sound wave is directly proportional to frequency.

Determining the pitch of a tone using savart’s wheel Savart’s wheel used to determine the pitch (frequency) of unknown tone. By increasing the speed of rotation the frequency increases, so the sound becomes sharp (high pitch).

Determining the pitch of a tone using savart’s wheel Number of wave produced = number of cycles (turns)(d) x number of gear’s teeth(n) F = number of cycles x no. of gear’s teeth time in sec (t)

problem Calculate the frequency of a musical tone similar to the frequency of a produced tone using Savart’s wheel rotated with a velocity of 960 cycles in two minutes, given that the number of teeth of the gear is 30 teeth. Time = 2 x 60 = 120 sec. F = number of cycles x no. of gear’s teeth time in sec (t) F = 960 x 30 = 240 Hz 120

Sound intensity It is the property by which the ear can differentiate between sounds either strong or weak. The measuring unit of sound intensity is watt/m 2. The measuring unit of noise intensity is Decibel.

Factors affecting the sound intensity The distance between the ear and the sound The amplitude of vibration of the sound The density of the medium through which the sound propagate The area of the vibrating surface The direction of the wind

The distance between the ear and the sound source Inverse square law of sound : The intensity of sound (I) at a point varies inversely with the square of the distance (d 2 ) between that point and the sound source. I α 1 d 2

G.R: The intensity of sound at a point varies inversely with the square of the distance between that point and the sound source. Because sound intensity is inversely proportional to the square of the distance between them.

The amplitude of vibration of the sound Sound intensity is directly proportional to the square of the amplitude.

Exercise Compare between the two given waves, concerning the pitch and intensity of sound. Sound pitch: wave A has higher pitch than wave B because the frequency of wave A more than that of wave B Sound intensity: wave A has more intensity than wave B because the amplitude of wave A is larger than that of wave B

The area of the vibrating surface The sound intensity increases when the source of sound touches a resonance body (box) due to increase of the surface area of the vibrating body.

G.R: Sound intensity increases when the sound source touches a resonance box. Due to the increase of the surface area of the vibrating body

The medium density

Sound intensity increases by increasing the density of the medium and vice versa. Sound intensity is directly proportional to the density of the medium which travels sound.

G.R: Sound intensity in case of the presence of carbon dioxide gas as medium is higher than that in case of air. Because the density of carbon dioxide gas is more than that of air since the intensity of sound is directly proportional to the density of the medium.

Wind direction The intensity of sound increases when the sound waves propagation direction is in the same direction of wind. The intensity of sound decreases when the sound waves propagation direction is in the opposite direction

Sound quality It is the property by which the human ear can distinguish between different sounds according to the nature of the source even if they are equal in intensity and pitch.

Sound quality When the tuning fork vibrates, it produces a simple pure tone known as fundamental tone/basic tone The tones produced from violin or piano are complicated formed of a fundamental tone associated by several harmonic tones which are higher in pitch and lower in intensity.

Sound quality Harmonic tones: They are tones that accompany the fundamental (basic) tone, but they are lower in intensity and higher inn pitch and differ from one instrument to another G.R: The human ear distinguishes between sounds from different sources even if they are equal in intensity and pitch. Due to the harmonic tones that associate the fundamental tone of the source of sound and are lower in intensity and higher in pitch

Types of sound waves Non-audible sounds Ultrasonic waves Infrasonic waves Audible sounds Sonic waves

Audible sounds Sonic waves: They are sound waves of frequencies ranging from 20 to Hz (20 KHz). The human ear transmits the effect of such waves to the brain which translates them into sound and audible tones.

Non-audible sounds Infrasonic waves: They are sound waves of frequencies less than 20 Hz. The human ear cannot hear infrasonic waves. These waves accompany the blowing of storms that preceding rainfall

Non-audible sounds Ultrasonic waves: They are sound waves of frequencies higher than Hz (20KHz). The human ear cannot hear ultrasonic waves. Some animals such as bats, dogs and dolphins can hear ultrasonic waves

G.R: The human ear can hear sounds of frequencies ranging from 20 to Hz. Because the ear transmits the effect of these waves to the brain which translates them into sound and audible tones. Some sound waves can not be heard. Because the frequencies of these waves are lower than 20 Hz or more than Hz, so the human ear cannot hear them as the effect of such waves cannot be translated by the brain into audible tones.

Applications of ultrasonic waves Medical field: Breaking kidney and ureter stones. Diagnosis of tumors Industrial field: Sterilization of food as milk Military field: Discovering of landmines.

If the frequency of the sound produced by touching a metallic plate with a gear in Savart’s wheel is 100 HZ. Calculate the number of the gear’s teeth, if the wheel rotates with speed 120 cycles/minute.

Calculate the time in minutes taken by Savart’s wheel to make 600 cycles, if the frequency of the sound produced by touching a metallic plate with a gear of 60 teeth is 300 Hz.