Science 2nd prep 2nd term unit 2 lesson 1 part 1

Sound: It is an external factor (or stimulus) that affects the ear causing the sense of hearing.

** sound is produced due to the vibration of bodies and it stops when the vibrating bodies stop their vibration.

sound waves are mechanical longitudinal waves that need medium to propagate.

Sound waves consist of compressions and rarefactions.

Sound waves propagate through media as spheres whose centre is the source of sound.

We hear sound from all directions that surround the sound source? Because the sound travels through air as pulses of compressions and rarefactions whose centre is the sound source.

What meant by: the wavelength of a sound wave is 1.5 m? It means that the distance between centers of two successive compressions or two successive rarefactions in such wave is 1.5 m.

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Properties of sound waves

Nature of sound waves:

Sound velocity:

Science 2nd prep 2nd term unit 2 lesson 1 part 1

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

** sound waves propagate through different media with different velocities.

Note sound travel through air at a velocity 340 m/sec.( it may exceed or become

less than this value ), sound velocity through solids is larger than that through liquids. Sound velocity through liquids is larger than that through gases.

Enrichment information: The velocity of sound through air depends on:

temperature of air air pressure. Humidity in air.

** sound velocity can be calculated by using waves propagation law:

Problem: Calculate the wavelength of a sound wave propagating through sea water with velocity 1500 m/sec knowing that its frequency is 10 kilohertz.

Solution: The frequency (F) = 10 × 103 = 10000 Hz.

Sound velocity(V) = wave frequency (F) × wavelength (λ)

Then λ = V / F = 1500 / 10000 = 0.15 m = 15 cm.

We can hear many and different sounds, these sounds may be:

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Sound velocity(V) = wave frequency (F) × wavelength (λ)

Properties of sound waves:

Science 2nd prep 2nd term unit 2 lesson 1 part 1 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.

1 - Musical tones: They are tones of uniform frequency and comfortable to be heard.

Examples: Violin, piano and reed pipe.

2 – Noise It is sound of non-uniform frequency and uncomfortable to be heard.

Examples: Drill , loudspeakers and horn of cars.

Real life application: Ear plugs.

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Sound

1 – Musical tones 2 - Noise

Science 2nd prep 2nd term unit 2 lesson 1 part 1 Ear plugs made f silicon are sold in pharmacies. They take the shape of the external ear canal, where these plugs are used to avoid the hazards of noise in loud places.

Sound pitch:It is a property by which the ear can distinguish between rough and sharp voices.

** sound is described as high pitched or low pitched sound, where:

high pitched sound is sharp (soft). Low pitched sound is rough (harsh).

So, it is said that:

the voice of women is high pitched as it is sharp. The voice of men is low pitched as it is rough.

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Factors that make us differentiate between sounds

2 – Sound intensity

1 - Sound pitch 3 – Sound quality

1 - Sound pitch

Science 2nd prep 2nd term unit 2 lesson 1 part 1

Note>>> as the sharpness of voice increases, the level of voice (sound pitch) gets higher.

Activity >>> to illustrate the concept of sound pitch and its relation with sound frequency.

Materials and tools: - big sized book. - Rubber string or (band). - Two pencils.

Steps: As shown in figure. Observation:

- the sound pitch changes as the length of the vibrating segment changes, where the sound becomes more harsher as the length of the string increase and becomes more sharper as the length of the string decreases.

- the number of vibrations produced in one second (frequency ) increases by decreasing the length of the string.

conclusion: - the sound pitch is a property of sound by which the

ear can distinguish between harsh and sharp voices. - The sound pitch depends on he frequency of the

sound source. - The sound pitch increases by increasing the

frequency and vice versa.

Therefore : the sharp tones have high frequency, while the harsh (or rough) tones have low frequency.

Exercise: When blowing in the bottles illustrated in the opposite figure.

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Science 2nd prep 2nd term unit 2 lesson 1 part 1 In which bottle can you hear a high pitched sound? And why?

Answer: From bottle (a) we hear a high pitched sound, because it is of high frequency, where frequency increases by decreasing the length of air column.

Note: >>> the frequency increases by decreasing the length of air column and vice versa.

Enrichment information: Doppler's effect: it is the apparent change in the frequency of a sound wave for an observer moving relative to the source of sound wave.

It is commonly heard when a vehicle (carfire) sounding a siren approaches you gradually, the sound pitch increases and decreases suddenly as it moves away

** Savart's wheel is used to determine the pitch (frequency) of an unknown tone.

Steps for determining the pitch of atone using savart's wheel:

1 – Listen to the tone you want to determine its pitch till your ear get used to it. 2 – Rotate savart's wheel at the same tine one of the gears teeth contacts a flexible metallic sheet ( as in figure).

3 – Increase the speed of rotation till you hear a sound similar to that of the unknown tone.

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Determining the pitch of a tone using savart's wheel:

Science 2nd prep 2nd term unit 2 lesson 1 part 1

4 – Calculate the number of turns (cycles) (d) taking place in specific duration and by knowing the number of teeth of the gear (n), you can determine the frequency of the tone as follows:

Frequency (F) =number of waves produced / time in seconds

From the figure : each gear consists of a number of teeth, each tooth produces a wave when it touches the metallic plate.

So that, number of vibrations (waves) produced = d × n Whered = number of cycles (turns). And n = number of gear's teeth.

Sound frequency (F) = number of cycles (d) / time (t) × number of gear's teeth (n).

Note >>> speed of rotation = number of rotations (turns) / time (t)

So that , by increasing the speed of rotation, the frequency increases and the sound becomes high pitched (sharp).

Problems: (1) 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 o the gear's teeth, if the wheel rotates with speed 120 cycles / minute.

Solution: Frequency (F) = no of gear's teeth (n) × no. of teeth (n) / time (t).

Then F = no of gear's teeth (n) × 120 / 1 × 60 = 100 × 60/120 = 50 teeth.

(2) 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.

Solution:Frequency (F) = no of gear's teeth (n) × no. of teeth (n) / time (t).300 = 60 × 600 / t Time (t) = 36000 / 300 = 120 seconds = 2 minutes.

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Science 2nd prep 2nd term unit 2 lesson 1 part 1

Questions on lesson: Complete the following statements: 1 – sound is considered from …………………………….. waves, because it needs a medium to travewl through.

2 – sound originates from ……………………….. of bodies.

3 – sound wave velocity = ……………………………………… × ………………………………………….

4 – the velocity of sound through solids is ……………………… than that through gases and its velocity through gases is ………………………………. Than that through liquids.

5 – sound wave which propagates through air with velocity 340 m/sec, and of frequency 20 Hertz, its wavelength equals ………………………………

6 - ………………………… is a sound of …………………… frequency which is produced from electric digger.

7 – ear plugs made of ………………………… are used to avoid the hazards of …………………….. in loud places.

8 – the human ear can differentiate between the sounds through three different factors, which are sound …………………………….. , sound ………………………. And sound …………………………………..

9 – sound of women is …………………………. So it is said that it has ………………….. pitched sound.

10 – sound of lion is ………………….. so it is said that it has …………………….. pitched sound.

11 – sharp tones have ……………………… frequencies, wile rough tones have …………… frequencies.

12 –the sound pitch depends on the ……………………….. of the ………………………………

13 – the sound pitch is a property by which the ear can distinguish between ………………… and …………………………….. voices.

14 – the frequency of the vibrating string is ……………………….. proportional to its length.

15 – in savart's wheel by using the same gear, the sound produced will be sharper by increasing its …………………………..

16 – in savart's wheel, frequency = no of rotations × ………………………… / ……………………………..

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Science 2nd prep 2nd term unit 2 lesson 1 part 1

Choose the correct answer: 1 – sound waves do not travel through …………………… a. water b. air c. vacuum d. wood.

2 – sound waves travel through ……………………. a. solids b. liquids c. gases d. a , b and c

3 – the sound produced from the school's bell is considered …………….. waves. a. longitudinal b. electromagnetic c. transverse d. longitudinal & transverse.

4 – all of the following indicate the nature of sound waves except ……………………… a. it is mechanical longitudinal waves. b. it propagate as spheres of compressions and rarefactions. c. it is velocity through air 430 m/s.d. no correct answer.

5 – the sound velocity is measured in …………………. Unit. a. Hertz b. metre c. decibel d. metre / sec.

6 – all of these sounds are of uniform frequency except the sound of ………………….. a. violin b. guitar, c. loudspeakers. D. piano

7 –sound wave that propagates through air with velocity 330 metre/sec and of wavelength 0.1 metre, its frequency equals …………………………..a. 330 K Hz b. 3300 Hz c. 33 k Hz d. 330 Hz

8 – the voice of Adham differs from that of Sara because they are different in ………………..a. age b. intensity c. pitch d. kind.

9 – the sound pitch increases by ……………………………… a. the decrease of frequency b. the increase of frequency c. the increase of amplitude. d.increase of the distance between ear and sound source.

10 – we can prove that the pitch of sound depends on the frequency of vibration of the sound source using ……………………… a. the resonance box b. stretched string of fixed length. c. savart's wheel d. the tuning fork.

11 – the sound of frequency 200 Hz is ………………….. than the sound of frequency 100 Hz. a. stronger b. sharper c. weaker d. harsher.

12 – the frequency of sound produced from a plate touching a gear of 20 teeth in savart's wheel when the wheel rotates 300 cycles / minute equals ………………………. Hz. a. 300 b. 15 c. 6000 d. 100

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Science 2nd prep 2nd term unit 2 lesson 1 part 1 13 – as the number of teeth of the gear in savart's wheel increases, the …………………….. of the produced sound increases.a. amplitude b. intensity c. frequency d. quality.

14 – as the velocity of rotation of the gear in savart's wheel decreases, the frequency decreases, consequently the …………………….. of the sound decreases. a. pitch b. type c. amplitude d. intensity.

15 – the frequency of the sound produced form savarts's wheel depends on ………………………..a. the sped of rotation of the gear only. b. the distance between the gear and you only. c. the number of gear's teeth only. d. a and c are correct.

Write the scientific term: 1 – the distance which is covered by the sound waves in one second. …………………………………..2 – a tone of irregular frequency that is produced from loudspeakers. ……………………………………3 – an instrument used to determine the frequency of unknown sound tone. …………………………………4 – characteristic by which the ear can differentiate between man and woman voice. ………………

Give reasons for : 1 – the explosions occurred on the sun surface can not be heard on earth? ………………………………………………………………………………………………………………………………………………2 – sound can be heard form all surrounding directions? ……………………………………………………………………………………………………………………………………………..3 –when you use savart's wheel, you change the speed of wheel rotation? ………………………………………………………………………………………………………………………………………………4 – the violin's player changes the length of strings during his play? ………………………………………………………………………………………………………………………………………………

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