2013 Year 7 A world of Machines Chapter 9

Key Concepts

How do levers, inclined planes, wheels and axles, gears and pulleys help makes our life easier?
Could robots take the place of teachers?

Science Quest 7
9.1 A helping Hand - levers
9.1 As simple as a spoon page 297
9.2 Hard as nails page 297
9.3 Pushing your barrow page 299
9.4 Get a load of this page 299
Understanding & Inquiring
page 301 Q’s 1-6 & Choose one of the following Q’s 7-13 and report your answer to the class
Words to Learn
Levers, fulcrum, load, effort, first class, second class, third class levers, force multipliers, mechanical advantage, speed multipliers
9.2 Pushing uphill – inclined planes
9.5 Inclined to make it easier page 302
9.6 Inclined planes on the move page 303
Understanding & Inquiring
Page303 Q’s 1-4
Words to Learn
Inclined plane, ramp, wedge, screw, thread, pitch
9.3 Wheels and axels in a spin - pulleys
9.7 Getting a handle on wheels and axles page 304
9.9 Lifting a load page 306
Understanding & Inquiring
page 307 Q’s 1-6
Words to Learn
Wheel and axle, pulley (single and double), block and tackle, newtons, spring balance, mechanical advantage
9.4 Getting into Gear - gears
9.10 Looking at gears page 308
Understanding & Inquiring
page 309 Q’s 1-4
Research Q 5 – how many devices can you list?
Words to Learn
Gear (driving, driven), teeth
9.5 Compound machines - robots
Research – in pairs choose one question from page 313 Q’s 13-16
Understanding & Inquiring
page 313 Q’ 1-9
Words to Learn
Compound machine, robot

Balancing levers using distance and mass
a load of 10 kg a distance of 2 metres from the fulcrum will balance an effort of 5kg 4 metres from the fulcrum.

a load of 20 kg 1 metre from the fulcrum will balance an effort of 10kg 2 metres from the fulcrum

a load of 30kg 2m from the fulcrum is balanced by an effort of 15kg 4m from the fulcrum

what is the pattern? Write it as a number sentence or algebraically.

Load x distance to F = distance to the effort x effort

Simple machines

1. Levers
These are a bar which have effort at one end and load at the other. In the middle (usually) is the fulcrum.

2. Inclined planes
a ramp is an inclined plane it allows you to lift loads by gradually moving up the slope.
Other examples include - blade, screw (inclined plane wrapped around an axle). Wedge, axe head, spade,

3. Wheels and axles
In some ways a wheel and axle is like lots of levers joined together around a central fulcrum. The outer edge of the wheel acts as a force multiplier when the effort is applied here. We use wheels as force multipliers when we are turning a door knob or using a screw driver to take out a screw.

The edge closest to the axle will act as a speed multiplier when force is applied here. The edge furthest from the axle turns faster than the axle.

Examples of wheels and axles.
Pulleys are a good example of wheels and axles
A pulley used by itself can alter the direction the effort moves. This means instead of lifting a load up by bending over it and lifting we could use a pulley and pull down to lift the load up.

Pulleys can offer a mechanical advantage. If we use 2 pulleys there is a mechanical advantage of 2. This means if a load exerts a force of 100N we could lift it with a 2 pulley system by applying an effort force of 50N.

In a 2 pulley system the load will move10cm the effort will move 20cm.

In a 4 pulley system the mechanical advantage is 4.
If the load is 100N what effort is required to move the load ? _
If the load moves 10cm how far will the effort move ? _

Gears are another example of wheels and axles. This time the wheels have teeth. They are usefull because the teeth of one gear interlock with the teeth of another gear.

We use gears to move very heavy loads. Its easier to turn a big wheel than a little wheel. This is a force multiplier
When a small wheel turns quickly the big gear is turned at a medium pace. This is a speed multilpier

Gear questions page 309
Questions 1 to 5

Mechanical advantage and wheels


Single pulley only changes the direction of the force of effort. So if the load was 500g it would require 5 N to lift it straight off the ground or 5 N using 1 single Pulley pulling it down
A 2 pulley system will halve the amount of effort required to lift a load- therefore 500g will require half the normal effort of 5N ie only 2.5 Newtons to move the load
a 4 pulley system will quarter the amount of effort required to lift a load. Therefore a load of 400g would normally require 4 N to lift it but with a four pulley system it would require only 1N to lift the 400g

Inclined Planes
The shallower the slope of an inclined plane the less force required tto move the load. BUT the longer the load must be dragged to move it to the desired height.

Compound Machines examples.

Your task is to design a compound machine that will
It must use at least 3 simple machines - this means it might use different classes of levers combined with a pulley system OR gears and pulleys and wheels and levers etc

You Do It

Virtual Simple & Compound Machines