Lesson Notes By Weeks and Term - Junior Secondary School 3

TERM: FIRST TERM

SUBJECT: BASIC SCIENCE

CLASS: JSS 3

REFRENCES

• BasicScience Made Easy for JSS Three by F.I Kehinde et al
• BasicScience Made Easy for JSS Two by F.I Kehinde et al
• STAN Integrated Science for JSS Three
• Precious Seeds Basic Science for JSS three by J.O Otugboyegaet al.

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WEEK NINE

TOPIC: SOUND ENERGY

CONTENT

• Introduction.
• Transmission of sound.
• Reflection of sound.
• Hearing.

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INTRODUCTION

Sound is a wave caused by vibration of matter. It is a property of vibrating objects. These objects may be solid, liquid or gases. If there is an elastic medium (i.e a medium which is capable of being compressed between the vibrating object and a suitable apparatus such as a microphone, ear of animals) noise or sound will be detected.

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Sound may be produced in a variety of ways, normally as a result of some mechanical disturbances on an object, causing it to vibrate.

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For example:

• A blow by a hammer on a piece of iron causes the iron (and the hammer) to vibrate for a short while.
• A guitar string vibrates under the rubbing action of the bow.
• A tightly stretched skin on a drum is set to vibrate when it is struck.
• Vocal cord of humans vibrate when air from the lungs pass out through the larynx
• An explosion sets the surrounding air into vibration.

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TRANSMISSION OF SOUND

This is the passage of sound from one point to another e.g. from one room in a building to another or from the street into a room in the building.�

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The transmission and production of sound can be demonstrated in the laboratory using a tuning fork. The tuning fork has two steel prongs which when struck with a hard surface gives sound. During the vibration, the prongs of the tuning fork present a hazy appearance due to their rapid to and fro movements. If the vibrating prongsare dipped into a beaker of water, the water is seen to be violently agitated. The transmission of natural vibration from the tuning fork to the water is called Resonance.

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Soundistransmitted through matter such as air, water or solid metals. The matter or material through which sound is transmitted is called a medium. Sound travels faster in solid than in liquid and faster in liquid than in gases. The speed of sound in dry air is 332 m/s, 1484 m/s in water and 5,120 m/s in iron.

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EVALUATION

1. What is sound?
2. Explain the transmission of sound.

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REFLECTION OF SOUND

When sound reflects off a special curved surface called a parabola, it will bounce out in a straight line no matter where it originally hits.

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Many entertainment stages are designed as a parabola so that the sound will go directly into the audience instead of bouncing on the stage. If the parabola is closed off by another curve surface it is called an ellipse. Sound will travel from one focus to another no matter where it strikes the wall.

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A whispering gallery is designed as an ellipse. If your friend stands at one focus and you stand at the other, his whisper will be heard clearly by you. No one in the rest of the room will hear anything. Reflection of sound is responsible for echoes.

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An echo is a sound that is reflected back to it source. While multiple overlapping echoes is called reverberation.

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HEARING

Hearing is the ability to perceive sound by detecting vibrations, change in the pressure of the surrounding medium through an organ called the ear. The inability of the ear to hear is called deafness. There are three main components of the ear: the outer ear, the middle ear and the inner ear.

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The outer ear includes the visible part of the ear (or the pinna), the auditory canal and the eardrum. Sound travel in waves and when these waves arrive at the eardrum they cause vibration. The eardrum amplifies the incoming air pressure waves to a single firm with a certain extent (amplitude): this allows fir the differentiation of sound.

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The middle ear �consists of a smaller air-filled chamber that is located behind the eardrum. Within the chamber are three smallest bones in the body known collectively as ossicles. The ossicles are; malleus (hammer), incus (anvil) and stapes (stirrup). The stapes is the smallest bone in the body. The ossicles aid the transmission and amplification of the vibration from the ear drum to the inner ear.�

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The innerear, which comprises the cochlea (a coiled canal filled with fluid) which is connected to auditory nerve cells which pass on the signal to the brain.

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EVALUATION

1. Explain the reflection of sound.
2. Explain ear, the parts of the hear and their function.

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GENERAL EVALUATION

1. Explain the mechanism of hearing.
2. How does reflection of sound occur?
3. What is work?
4. Explain how energy is transfer in a working vehicle.
5. What is power

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READING ASSIGNMENT

Precious Seeds Basic Science for JSS Three by J.O Otugboyega et al. Chapter 20. Pages 114-116

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WEEKEND ASSIGNMENT

1. Which of the following cannot produce sound?� A. Guitar� B. Brain� C. Turning fork D. Metals
2. Which of the following is part of the outer ear� A. Stapes� B. Pinna� ,C. Auditory nerves� D. Hammer
3. The reflection of sound back to be source is called ___� A. Echo� B. Reverberation� C. Noise D. cacophony
4. The speed of sound in vacuum is� A. 332m/s� B. 1484 m/s� C. 5120 m/s� D. 0 m/s
5. Sound of distorted frequency is called� � A. Noise� B. Echo� C. Music� D. Reverberation

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THEORY

1. Why do churches have dome shaped roof?
2. Why is lightening seen before thunder is heard?