MACHINES

Machines are devices which use the action of a force or convert one type of energy into another.For example, a bicycle is a machine which transforms human energy into mechanical energy.

Machines save us time and physical effort.

TYPES OF MACHINES

Some machines, such as pulleys, are very simple because they have very few components. Other machines, such as computers, are complex because they have many components. 

Machines can be classified depending on the energy source. There are machines which work with:

- Human energy, such as a bicycle or a hammer.
- Water or wind, such as a watermill or a windmill.
- Fuel, such as a car or a gas stove.
- Electricity, such as a washing machine or a mobile phone.

MACHINES WITH PRODUCE MOVEMENT

Many machines produce movement, such as escalators, cars or food blenders. These machines have a motor or an engine. The motor converts fuel or electrical energy into movement.

THERMAL MACHINES

Thermal machines, such as heaters and air conditioners, produce heat or cold.

INFORMATION-PROCESSING MACHINES

Information-processing machines are used for communication and calculations. For example, we can communicate with others using mobile phones, and we can make calculations on computers.

ACTIVITY " MACHINES"

READ THESE SENTENCES AND CORRECT THE WRONG INFORMATION.

1. A bicycle is a machine which transforms mechanical energy into human energy.
2. Pulleys have many components.
3. A hammer works with wind energy.
4. A washing machine works with fuel.
5. Computers are simple machines.

CASING AND STRUCTURE

The casing is the outer part of a machine. It protects the machine from dust, moisture and damage. The structure is the frame of the machine, and it supports the weight.

OPERATING PARTS AND MECHANISMS

The operating parts are the components of a machine, such as wheels, axles, springs and chains.

An mechanism is a group of operating parts which work together to perform a specific task. For example, on a bicycle, the gears and chain form a mechanism.

ENGINES AND MOTORS

An engine or a motor is the part of a machine which produces movement.

- Combustion engines use chemical energy from fuel. Cars and aeroplanes have combustion engines.

- Electric motors use electrical energy. Electric machines, such as trains or cameras, have electric motors.

ELECTRICAL CIRCUITS AND ELECTRONICS

Machines which use an electrical current have electrical circuits.

- Electronic circuits are electrical circuits with very small components.

- Microchips, the smallest circuits, have tiny electronic circuits. Microchips are used in digital cameras, telephones and many other electronic devices.

ACTIVITY "INSIDE A MACHINE"

READ THESE DEFINITIONS AND WRITE THE CORRESPONDING WORDS

1. The outer part of a machine.
2. The frame of the machine which supports the weight.
3. The components of a machine, for example, wheels, axles,etc.
4. A group of operating parts which act together to perform a specific task.
5. Engines which use chemical energy from fuel.
6. Components which have tiny electronic circuits and are used in digital cameras, telephones, etc.

SOUND

SOUND is a form of mechanical energy produced by the vibration of an object, such as a string on a guitar, a drum or even our vocal cords.

Sound travels in waves through solids, liquids and gases. It travels through air at 340 metres per second, a speed much slower than the speed of light.

REFLECTION OF SOUND

An echo is the reflection of sound from the surface of an obstacle. Sound takes time to bounce off the obstacle and return to our ears, so we hear both the original sound and the echo.

When the original sound is reflected from walls and objects in an enclosed space, we hear a series of echoes. This is called reverberation. Cathedrals, gymnasiums and indoor swimming pools are good places to hear reverberation.

QUALITIES OF SOUND

INTENSITY: intensity depends upon the amplitude of the sound wave. If the sound is loud, the amplitude is large. If the sound is soft; the amplitude is small.

PITCH: the pitch of a sound depends on the frequency of its sound waves. Pitch enables us to differentiate between the high notes and the low notes made by a musical instrument.

TONE: tone enables us to identify the source of a sound with the same frequency and intensity. For example, a guitar does not sound like a saxophone. That is because every musical instrument has a unique tone. Every person´s voice is different because every voice has a unique tone. 

ACTIVITY SOUND

COMPLETE THESE SENTENCES WITH THE CORRECT WORD

echoes/ waves/ mechanical/ reflection/ vibration/ slower/ air

1. Sound is a form of ...... energy.
2. Sound is produced by the ......... of an object.
3. Sound travels in ........
4. Sound travels through ....... at 340 metres per second.
5. Sound travels much ......than light.
6. An echo is the .........of sound.
7. Reverbration is a series of ......

LIGHT

LIGHT is a form of energy which enables us to see. Light moves very rapidly, at 300,000 km per second. It travels in all directions, but always in a straight line. Thus, if light meets an obstacle, the obstacle blocks it, and a shadow is formed.

OBJECTS AND LIGHT

- Transparent objects or substances, such as glass and air, allow light to pass.

- Translucent objects, such as a thin piece of paper, allow some light to pass.

- Opaque objects, such as a book or a pencil, absorb or reflect light.

REFLECTION

When light hits an opaque object, it is reflected and changes direction. This is called reflection. Reflected light enables us to see things. We can see the Moon when it reflects light from the Sun.

LIGHT AND COLOURS

WHITE LIGHT is made up of infinite colours. In a rainbow, white light is separated into different colours.

The colour of an object is the colour of the light which the object reflects. For example, a blue object absorbs every colour of light except blue and reflects blue light into our eyes.

REFRACTION

When light passes through one transparent medium to another, it bends and changes direction. This is called refraction. Lenses refract light. Lenses can be convex or concave.

ACTIVITY " LIGHT"

ANSWER THESE QUESTIONS

1. How fast does light travel?
2. What makes a shadow form?
3. What words describe objects which absorb or reflect light / allow some light to pass/ allow light to pass?
4. What is reflection?
5. What happens in a rainbow?