Science notes, unit 10

Machines

Textbook Science Year 4 (DLP), pages 169–184

What this chapter covers

You can name the three parts of a lever, the load, the fulcrum and the force, and find them in everyday tools (10.1.1, 10.1.2)
You can explain how the distance of the load from the fulcrum changes the force needed to lift it (10.1.3)
You can name the seven simple machines and say what each one is used for (10.2.1)
You can choose simple machines to solve a problem and explain why (10.2.2)
You can say what a complex machine is and name the simple machines inside one (10.2.3)
You can describe the characteristics of a sustainable machine (10.2.4)

Machines make our work easier and faster. In this unit you will meet the lever, learn how it works, and then learn about the seven simple machines and the complex machines that are made from them.

10.1Lever

A lever is a simple machine used to lift or pry up a load. It has three parts: the load, the fulcrum and the force.

Part	What it is	Opening a paint can with a screwdriver
Load	The weight of the object we want to move	The lid of the can
Fulcrum	The point that supports and balances the rod	The tip of the screwdriver touching the can
Force	The push or pull we use	The hand pushing the screwdriver down

A hand pushes a screwdriver down to lift the lid of a paint can; the lid is labelled load, the tip fulcrum and the hand force — A screwdriver is a lever. The lid is the load, the tip is the fulcrum and the hand gives the force.

Figure after Science Year 4 (DLP), p.170.

Three levers with load, fulcrum and force labelled: a broom sweeping, a hammer pulling out a nail and tongs gripping ice — More levers: sweeping, pulling out a nail and gripping ice.

Figure after Science Year 4 (DLP), p.170.

The position of the three parts is not the same in every lever. Always look at where the rod rests (fulcrum), what is being moved (load) and where you push or pull (force).

Distance of the load from the fulcrum

Two men want to move a big rock with a stick. When they push the small rock (the fulcrum) closer to the big rock, the rock lifts more easily.

The closer the load is to the fulcrum, the less force is needed to lift it. The farther the load is from the fulcrum, the more force is needed.

Investigation: lift a wooden block with a 50 cm ruler, placing the fulcrum triangle 25 cm, 20 cm and then 15 cm from the block.

Variable	What it is in this investigation
Manipulated (changed)	Distance of the fulcrum triangle from the block (25, 20, 15 cm)
Responding (measured)	Force needed to lift the block
Constant (kept the same)	The block, the ruler, the way you press

At 25 cm the block is hardest to lift. At 15 cm it is easiest.

Remember: near the fulcrum, small force.

A gardener pushes down on a long wheelbarrow handle. The load is moved nearer to the wheel. Is it easier or harder to lift? Why?

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Easier, because the load is closer to the fulcrum (the wheel), so less force is needed.

10.2Simple machines and complex machines

A simple machine is a tool that helps us do work more easily and quickly. Each type has its own use.

Simple machine	What it is	Example
Wheel and axle	A wheel fixed on a rod called an axle	Door knob
Lever	A rod resting on a fulcrum, to lift or pry up a load	Broom
Screw	A grooved cylinder turned into an object to join or tighten two parts	Bottle and its cap
Gear	Wheels with teeth (jagged edges)	Gears in a clock
Pulley	A grooved wheel that a rope passes through, to lift or lower a load	Pulley on window blinds
Inclined plane	A tilted flat surface with ends at different heights	Stairs
Wedge	A tool with one pointed end, to cut, hold or stop an object	Knife, doorstop

A classroom scene showing a door knob as a wheel and axle, a broom as a lever and a bottle cap as a screw — Wheel and axle, lever and screw in the school.

A classroom scene showing a clock with gears, a window blind pulley, a step ladder as an inclined plane and a doorstop as a wedge — Gear, pulley, inclined plane and wedge in the school.

Figures after Science Year 4 (DLP), pp.174-175.

Name the simple machine in (a) a door knob, (b) the stairs, (c) a doorstop.

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(a) Wheel and axle (b) Inclined plane (c) Wedge

Using simple machines to solve problems

Teruni's father cannot lift heavy boxes into a lorry. A tilted board (an inclined plane) makes loading easier. A trolley (wheel and axle) makes it faster. The more simple machines we use, the easier and faster the work becomes.

A girl and her father with a lorry; a tilted board and a trolley help move boxes — An inclined plane and a trolley solve the problem.

Figure after Science Year 4 (DLP), p.177.

Example: choosing a machine

Problem: lifting a bucket of paint to a high place. Suggestion: a pulley with a rope. Problem: reaching a high wall. Suggestion: a ladder (inclined plane).

Complex machines

A complex machine is a tool made of a combination of more than one simple machine.

A garden scene: garden shears with a screw and wedge, a step ladder as an inclined plane, a wheelbarrow with lever, wheel and axle and screw — Garden shears: screw and wedge. Wheelbarrow: lever, wheel and axle, screw. Step ladder: inclined plane.

Figure after Science Year 4 (DLP), p.180.

A bicycle (gear, screw, wheel and axle) and a mechanical pencil sharpener are also complex machines.

A sustainable machine is durable (not easily damaged), profitable, does not harm the environment, and is easy and safe to use.

A bicycle is a good example: it is easy to use, needs no fossil fuel and does not pollute the air.

A complex machine has two or more simple machines. A screwdriver alone is just one lever.

Why is a bicycle a sustainable machine?

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It is easy to use and does not need fossil fuel, so it does not pollute the environment.