Sound And How It Travels

Sound is important to us since it allows us to communicate with each other. Some sounds are unpleasant to our ears and these we sometimes call noise. For example, we do not like the noise made by heavy traffic, or the noise of thunder.

All sounds, whether they are pleasant or unpleasant, are a form of energy created by vibrating objects. A vibration is a rapid movement backwards and forwards. The movement is usually so fast that it cannot be seen. For example, when we speak or sing, even when we whisper, our vocal cords vibrate. The vibrations cause pressure changes in the air around us and these spread out in the form of waves. These waves go in every direction. Even if you are standing with your back to someone, that person will hear you talking.

When we speak to someone our vocal cords vibrate, and these same vibrations are picked up by the other person’s ear-drums, which also vibrate. Sound, therefore, can travel through air, but how does this happen? The air around us consists of millions and millions of tiny particles, which are known as air molecules. When an object vibrates, such as your vocal cords, it pushes the first layer of molecules forward. These push on the second layer and bounce back slightly. The second layer hits the third layer and so on. A ripple of energy moves outwards and reaches the ear of the person listening.

This is how we communicate with each other. A person who is deaf is severely handicapped, since speech is our primary means of communication. The ears of a deaf person do not pick up the vibrations made by our vibrating vocal cords.

Sound waves can travel through other things in addition to air. They can travel through liquids such as water, and through solids such as metal pipes. Knock a water pipe in one part of the house and someone else can hear it in another part. However, sound can not travel in a vacuum, that is to say in empty space, because there are no air molecules to carry the sound waves. This is why astronauts in space have to talk to each other by radio. Although radio waves can travel through space, sound waves cannot.

Sound takes time to travel from one place to another. Imagine you are on a sports field watching the start of a race. You see a puff of smoke as the starter fires the pistol, and you see the athletes starting to run. An instant later you hear the noise of the gun. This is because light travels much faster than sound. In the same way, in a thunderstorm you normally hear the thunder a few seconds after you see the lightening.

Sound travels in air at a speed of about 1,200 kilometres per hour at sea level. As the medium through which sound travels becomes denser, the speed becomes higher. In water, for example, sound travels at about four times the speed it does in air. Because the atmosphere becomes less dense the higher we go, the speed of sound is also reduced.

In supersonic aeroplanes, speed is generally measured by Mach numbers. Mach 1 is the speed of sound, whatever the altitude. When an aeroplane is travelling at Mach 2, it is travelling at twice the speed of sound, and so on. As an aeroplane approaches Mach 1, strange things happen. First, there is buffeting, and shock waves build up over the airframe. As it passes Mach 1 a shock wave is formed causing the sonic boom which sounds like an explosion. This can cause damage to buildings on the ground. There are special regulations to stop supersonic flights over populated areas.

If a sound wave reaches a large, hard, smooth object, it can bounce back to make an echo. Echoes can be useful and fishermen use them to find shoals of fish. Modern fishing boats are equipped with sonar, an instrument which sends sound waves down into the water. If the sound waves strike a shoal of fish, the sound reflects, or echoes back to the instrument. This shows the direction and depth of the shoal.

Sometimes in a large hall, or theatre, sounds will bounce around the walls and ceiling. This makes it difficult to hear speech or music clearly. If a sound wave reaches a large, hard, smooth object, it can bounce back to make an echo. Curtains, carpets or special tiles known as baffles can be used to deaden the echoes. As a hall fills up with people, their clothes absorb sound too. Designers have to consider this when they plan how speech or music will sound inside these buildings. This science is known as acoustics.

(from "Language and Communication" Cambridge Science Universe)

Exercises

Comprehension Questions

1. Using information from the text, write definitions of the following terms:
1. a vibration
2. a vacuum
3. Mach
4. echo
5. a baffle
6. acoustics


2. Match the correct speed from the box below with the events in a-e.

Speed	Event
0 (zero) kph 1,190 kph 1,200 kph 2,400 kph 4,800 kph	speed of sound in water speed of sound in space speed of sound at sea level speed of an aircraft at Mach 2 at sea level speed of sound at 5,000 metres (approximate)

 

Using information from the text, mark the answers below T if the statement is True, F if the statement is False or NI if there is insufficient information in the text to decide if the statement is True or False.

T / F / NI	Statement
.... .... .... ....   ....	A vibration causes unpleasant sounds. Our vocal cords do not vibrate when we whisper. When we sing, the air vibrates more slowly. Astronauts can not hear speech in space because it is a vacuum. Sonar can be used to identify aeroplanes.

 

Reflection Questions

Explain how you found each answer

   

Represent the information from this text as a diagram.

   

What did you learn from this text?


How did you find the answers to the exercises? Refer to the text.

What advice could you give on how to understand definitions, descriptions and classifications from texts?


 


Defining, Classifying and Categorising

3. Look at the following examples from the text and answer the questions that follow.

 

1. Some sounds are unpleasant to our ears and these we sometimes call noise.
2. All sounds, whether they are pleasant or unpleasant, are a form of energy created by vibrating objects. A vibration is a rapid movement backwards and forwards.
3. The vibrations cause pressure changes in the air around us and these spread out in the form of waves.
4. The air around us consists of millions and millions of tiny particles, which are known as air molecules. When an object vibrates, such as your vocal cords, it pushes the first layer of molecules forward. These push on the second layer and bounce back slightly. The second layer hits the third layer and so on.
5. Sound takes time to travel from one place to another. Imagine you are on a sports field watching the start of a race. You see a puff of smoke as the starter fires the pistol, and you see the athletes starting to run. An instant later you hear the noise of the gun. This is because light travels much faster than sound. In the same way, in a thunderstorm you normally hear the thunder a few seconds after you see the lightening.
6. If a sound wave reaches a large, hard, smooth object, it can bounce back to make an echo.
7. Modern fishing boats are equipped with sonar, an instrument which sends sound waves down into the water. If the sound waves strike a shoal of fish, the sound reflects, or echoes back to the instrument. This shows the direction and depth of the shoal.
8. Curtains, carpets or special tiles known as baffles can be used to deaden the echoes.

Identify the verb in each sentence that helps you to understand that the text is defining a term.

What other verbs do you know that mean something similar?

What other language items help you to identify a definition?

Apart from defining terms, what else does the text do to help you understand the terms?

Can you improve your answer to question 8?

Look at the following texts and write definitions for the terms that follow. Underline the language that helps you understand the definitions.

 

1. Simple Calculations   (B) A new number type is necessary for numerical computing. In our discussions of text processing, we used integers, which are useful for counting, for referencing specific characters in a string, and for other numbering situations. But this number type cannot take on fractional values, as in 2 1/5, and the values cannot be too large in a positive or negative direction. On many machines, an integer may not be larger than 32,767 or smaller than -32,768, and on all machines there will be limitations on the maximum and minimum values. In general computational applications, we need a number type that can take on fractional as well as very large and very small values.

The answer to this need is the real type, which represents numbers in two parts: the significant digits and an exponent. The number 177 might be represented as 1.77* 10² where 1.77 gives the significant digits and 2 is the exponent. The actual value of the number can always be retrieved from the representation (1.77 * 10² = 1.77 * 100 = 177) and the representation can be efficiently stored in the machine. This number type, which solves the two problems posed by integers and requires relatively little computer memory, is used almost universally on modern computers. We will not discuss in detail exactly how the numbers are stored except to say that two storage areas are needed, one to hold the significant digits and one to hold the exponent, and the sizes of these areas are sufficient for most applications. For example, if we use the real type with typical versions of Turbo Pascal, the largest number will be around 10³⁸, the smallest number will be around 10^-45, and the number of significant digits will be about 11 or 12.

(from Biermann, A. (1998) "Great Ideas in Computer Science" Chapter 3)

 

2. Specification.

   The first stage is the specification stage. The specification says what the program is to do, what task it is to perform, not how to do it. Most programming problems are written in English as a description of a problem or something to be achieved. This is known as a functional specification. The program must meet the specification. A program can be well written and error free, but, if it does not meet the specification, it is a useless program.

   If a building contractor is asked to build a five-storey apartment building of 2 bedroom apartments and he builds a seven-storey building of 1-bedroom apartments, he is unlikely to be paid for the job.

(from McFadyen, J. (1999) "The Programming Process")

Using information from the texts, write definitions of the following terms:


Text a
1. integer
2. real
3. exponent

Text b
4. Specification


 


Discovery

4. Relate what you have learned to other work this semester by carrying out these tasks.

 

1. Find examples of definitions and classifications from readings that you have been asked to do since the beginning of the year.
2. Find at least five different ways of defining and five different ways of classifying from the readings.
3. Copy these examples into your vocabulary journal.
4. Make notes on the language that identifies these examples of definitions or classifications.
5. Show them to your teacher.