MACHINES & STRUCTURES

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SCIENCE 5.

UNIT 7. MACHINES & STRUCTURES

CONTENTS: 1.– MACHINES: simple / complex.

2.– Simple machines: Wheel, lever, screw, inclined plane, pulley, wedge.

3.- Complex machines: parts.

Casing, motor, circuits, mechanical elements...

4.– Tools: hand tools / power tools.

C.E.I.P. SANTA ANA (Madridejos)

A machine is something that helps us to do a work with less effort.

There are simple machines and complex machines.

1 Scissors

5.– STRUCTURES: types, parts…

6.– Technological advances, scientists and inventors.

1.– MACHINES. A machine is something that helps us to do a work with less effort. For example a bike helps us to move easier than walking or running, a calculator helps us to save time when we must do calculations.

There are two types of machines: simple machines and complex machines.

1.1.– SIMPLE MACHINES. A simple machine has only one or a few parts or components. From ancient times humans have used this kind of machines.

A.– Wheel & axle: The invention of the wheel was into the Neolithic period.

A wheel is a circular component that rotates on an axle, and reduces friction, so makes easier the movement.

The wheel and the axle help us to transport heavy objects in an easy way.

Washing machine

Calculator 2

wheel axle

Model of an old cart.

First-class lever: Fulcrum in the centre. effort

B.– Lever: This machine is formed by a rigid bar, that moves around a fixed support called fulcrum. It is used to transmit a force, to move heavy objets…

There are three classes of levers, depending if the fulcrum, the load or the effort are in the centre.

FULCRUM

3 Second-class lever: Load in the centre.

.– First-class lever: Fulcrum in the centre. .– Second-class lever: Load in the centre. .– Third-class lever: Effort in the centre.

effort fulcrum

LOAD

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USEFUL WORDS: .– machine .– wheel .– fulcrum .– screw

.– simple .– axle .– effort .– jack

Load

.– complex .– lever .– load

C.– Screw: We use a screw to hold things together or lift objects.

Turning a screw is easier than pushing the screw directly.

A car jack is one example of using a screw to push up a heavy object from the ground.

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Third-class lever: Effort in the centre.

EFFORT

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fulcrum

Screw can hold things together.

Load

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2

C.E.I.P. SANTA ANA (Madridejos)

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D.– Inclined plane: An inclined plane or ramp, is a flat supporting surface with one end higher than the other, used for raising or lowering heavy objects.

It’s easier to push an object up on an inclined plane than to lift it vertically. inclined plane 2 Pulley

E.– Pulley: This machine has a wheel, an axle and a rope or chain.

If we pull down the rope, we lift an object fixed to it.

Pulling the rope is easier than lifting the object using our body.

An old pulley.

F.– Wedge: This machine has a pointed end and one thicker end (triangled-shape), that is used to split something or to separate two things. We can do it push down with a hammer.

Effort

Load

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Simple machines: formed by one or a few components.

Wheel and axle / lever / screw / inclined plane / pulley / wedge Splitting a trunk with wedges.

5 1.2.– COMPLEX MACHINES. A complex machine has a lot of components and simple machines working together. It needs electricity or other kind of energy to work.

Main parts of a complex machines:

a.– Casing: is the outer part of the machine, and protects it. b.– Motor: some machines like cars, drills… have motors to produce movement (electrical or combustion motors). c.– Electric and electronic circuits, microchips... control different functions of the machine. They need electricity to work. d.– Sensors and screens: Sensors receive information from the machine and from the exterior. Screens give us information about the functioning of the machine.

Casing

Sensors & screen

Motor

Gears, pinions, chains...

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e.– Mechanical elements:

e.1.– Gears change direction, speed, amount of a force…

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Complex machines: has lots of components.

Casing / motor / circuits / sensors / screens / gears / rack and pinion / chain drive

e.2.– Rack and pinion convert rotational motion into linear motion.

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USEFUL WORDS: .– inclined plane .– complex machine .– screen .– rack & pinion

.– pulley .– wedge .– casing .– sensor .– microchips .– gears .– chain drive

e.3.– Chain drive is used for transmission of mechanical power in machines (bikes…)

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pinion rack

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4.– TOOLS: Primitive humans started to use tools thousands of years ago. First tools were made of stone, wood or parts of animals like bones. Later they were made of metals, that were harder and more useful.

Nowadays there are specific tools for every type of job, and we can divide them into groups: Hand tools and power tools.

C.E.I.P. SANTA ANA (Madridejos)

Prehistoric stone tools.

A tool is any physical instrument that you use with your hands to make or repair something easier.

There are hand tools and power tools.

Hand tools

Carpentry tools from 16th century.

Power tools

Screwdriver

Cement mixer

Hammer Drill

Pliers Scissors

Food mixer

Adjustable Wrench

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Lawnmower

Microwave oven

4.1.– Hand tools: They are tools that you can only use them with your hands.

They do not need any power or another type of energy.

Some examples of hand tools are hammers, screwdrivers, scissors, wrench, pliers...

4.2.– Power tools: They are tools that work with a power source. The most common have electric motors. They are used in industry, contruction, gardening, housework, drilling, cutting...

5.– STRUCTURES: TYPES & PARTS.

NATURAL STRUCTURES

A structure is a framework formed by interconnected parts, that can resist weights and forces, and must be stable and strong.

There are structures in everywhere. In nature, living beings are formed by structures. A structure must sustain more than its own weight and other forces like wind, water... so they must be strong.

For example, vertebrates are formed by a skeleton.

The skeleton is a structure made up by bones, some invertebrates have an exoskeleton that holds and protects the rest of the body.

2 5.1.– Types of structures: There are two types of structures: .– Natural structures: Produced in nature by living beings, like skeletons. In plants, the structure of cells can support the weight of the plant. Birds built nests for their baby birds… .– Artificial structures: designed and made by humans.

Examples of them are buildings, cathedrals, bridges... .– tools .– screwdriver .– lawnmower

.– hand tools .– pliers .– food mixer

.– power tool .– wrench .– framework

Paper wasps nest.

Storks nest.

ARTIFICIAL STRUCTURES

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.– hammer .– drill Structure of a house.

Structure of Tower Bridge (London).

4 C.E.I.P. SANTA ANA (Madridejos)

5.2.– Parts of a structure: Most of structures must resist three kind of forces.

If we think of a house...

1.– The weight of the structure itself (metal structure).

2..– Extra weight (walls, windows, furniture, people…)

3.– Other forces (wind, water, earthquakes…)

Beams Triangular structures

Pillars

Most of structures have common parts: .– Foundations: base of the building (underground). .– Pillars: vertical parts. .– Beams and girders: horizontal parts. .– Archs, staircase, triangular structures...

Staircase

1.–TECHNOLOGICAL TISTS & INVENTORS.

ADVANCES,

SCIEN-

Structure of a block of flats.

From prehistoric times, people have improved tools and machines. We are using more and more machines everytime for everything.

Nowadays, there are lots of technological advances that we use instead of old inventions. Normally machines and inventions are improving because scientists and inventors are working on new technology everyday.

In ancient times, sailing was very complicated because it was very easy to get lost in the sea. At the end of the Middle Ages, the compass was brought from China, so Christopher Columbus could discover America.

Nowadays we do not use the compass, instead, we use GPS (Global Positioning System) in our mobiles, cars, planes...

Foundations

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2 From compass to GPS.

Cars at the end of 19th century were very diffent than current cars, because of the technology depeloment.

Mercedes Benz (1886) speed 19 km/h.

Volkswagen beetle (1938)

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Renault (1889) speed 50 km/h.

Seat 600 (1957)

.– foundations .– pillars .– triangular structure

Ford T (1901)

Jeep Grand Cherokee (2010)

Citroën Traction Avant (1934)

Ferrari (prototype)

.-beams /girders .– arch .– GPS (Global Positioning System)

.– staircase