Simple Machines — Levers and Pulleys
In 2019, Sydney Metro Northwest workers used pulley systems giving a mechanical advantage of 8, so one worker could lift 2,400 kg of tunnel segment — a load that would otherwise need a crew of 8 people.
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Q1 · A crowbar can lift a rock that you couldn't lift with your hands. Are you creating energy from nowhere?
Q2 · Name 3 simple machines you used before getting to school this morning.
● Know
- The 6 types of simple machines
- The 3 classes of levers and their defining features
- How fixed and movable pulleys differ
● Understand
- Mechanical advantage: output force compared to input force
- Why using a machine never creates energy (force–distance trade-off)
- Why machines with MA > 1 require you to push over a longer distance
● Can do
- Classify levers as Class 1, 2 or 3 using fulcrum/effort/load positions
- Identify simple machines in everyday Australian contexts
- Estimate whether MA > 1, = 1 or < 1 for a given machine
- Simple machine
- Lever
- Fulcrum
- Pulley
- Mechanical advantage
- The pivot point around which a lever rotates
- Output force ÷ input force — how much a machine amplifies force
- Device with few moving parts that redirects or amplifies force
- Grooved wheel and rope used to change direction or reduce force
- Rigid bar that rotates around a fixed point
Put a ruler across a pencil lying on a desk, then push one end down — the other end rises, lifting whatever you placed on it. You've just built a lever: a rigid bar pivoting around a point, multiplying your force. Humans have used this trick for 10,000 years, and every crowbar, seesaw, bottle opener, and nail puller is doing exactly the same thing.
A simple machine is a device with few or no moving parts that changes the direction or magnitude of a force. The 6 types are:
- Lever — rigid bar pivoting around a fulcrum (crowbar, seesaw)
- Wheel and axle — large wheel attached to smaller axle (door handle, steering wheel)
- Pulley — grooved wheel and rope (crane, flagpole)
- Inclined plane — sloped surface (wheelchair ramp, road up a hill)
- Wedge — two inclined planes joined (axe, door stop)
- Screw — inclined plane wrapped in a spiral (bolt, jar lid, auger)
Mechanical advantage (MA) — qualitatively: output force divided by input force. If MA > 1, the machine multiplies your force. The trade-off: you must push or pull over a longer distance to do the same amount of work. You can never get more energy out than you put in.
Every lever has three parts: Fulcrum (F) — the pivot; Effort (E) — where you apply your force; Load (L) — what you are moving. The class depends on their order along the lever.
| Class | Order | MA | Examples |
|---|---|---|---|
| Class 1 | E — F — L or L — F — E (fulcrum in the middle) | Can be >1 or <1 | Seesaw, crowbar, scissors, pliers, balance scale |
| Class 2 | F — L — E (load in the middle) | Always >1 | Wheelbarrow, nutcracker, bottle opener, stapler |
| Class 3 | F — E — L (effort in the middle) | Always <1 (speed & range trade-off) | Tweezers, fishing rod, sugar tongs, human forearm |
Class 3 levers have MA < 1 (you apply MORE force than the load), but gain speed and range of motion — a fishing rod makes a small arm movement flick a line very far.
Pulleys:
- Fixed pulley — attached to a ceiling or beam. Changes the direction of the rope but MA = 1 (same force in as out). Useful because you pull down instead of up.
- Movable pulley — attached to the load. Reduces force needed (MA ≈ 2 qualitatively) but rope must be pulled twice as far.
- Block and tackle — multiple pulleys combined. Used in ship rigging, construction cranes, and mine-shaft hoists. MA increases with each additional rope segment supporting the load.
Simple machines are everywhere in Australian life, from farms to construction to the tools you use every day.
| Machine | Type | Australian example |
|---|---|---|
| Lever (Class 1) | Crowbar | Post fencing on outback stations; breaking rock in quarries |
| Lever (Class 2) | Wheelbarrow | Garden centres, building sites across Australia |
| Block and tackle | Compound pulley | Tower cranes in Sydney CBD; mine-shaft hoists in Broken Hill |
| Inclined plane | Ramp | Wheelchair access ramps (required by the Disability Discrimination Act); loading docks at warehouses |
| Wedge | Axe | Timber chopping (bushfire preparedness, rural Australia); ploughs in farming |
| Screw | Auger / drill bit | Post-hole borers for farm fencing; foundation screws for construction |
Indigenous Australian tools also use simple machine principles: digging sticks use lever action; stone knapping (making sharp stone tools) uses the wedge principle — a sharp wedge concentrates force to split rock or bone.
A compound machine combines multiple simple machines. A bicycle uses: a wheel and axle (wheels, pedal cranks), levers (brake levers, pedals), and inclined planes hidden in the gear teeth.
- Crowbar
- Wheelchair ramp
- Axe head
- Crane hoist rope
- Wedge — concentrates force along a thin edge
- Class 1 lever — fulcrum between effort and load
- Pulley (block and tackle) — redirects and multiplies force
- Inclined plane — trades shorter distance for less force
Wrong: "A machine with MA > 1 saves energy." Machines never save energy. If you apply half the force you move twice the distance — the same energy is used. The trade-off is always there.
Right: Machines save force, not energy. You always move over a greater distance to compensate — total energy in = total energy out (plus losses to friction).
Wrong: "Class 3 levers are useless because MA < 1." Class 3 levers trade force for speed and range of motion. A fishing rod turns a small arm movement into a long cast. The human forearm is a Class 3 lever — essential for fast, precise movement.
Right: Class 3 levers give greater speed and range of movement in exchange for applying more force than the load. Very useful for tools requiring precision or speed.
Wrong: "A fixed pulley halves the force needed." A fixed pulley only changes the direction of force (MA = 1). Only a movable pulley or block-and-tackle system actually reduces the force needed.
Right: A fixed pulley lets you pull down instead of up, but doesn't reduce force. A movable pulley (or block and tackle) reduces the force required.
You want to lift a 400 N engine block out of a car using rope and pulleys. You have one fixed pulley bolted to the ceiling and 20 m of rope. Predict: does this fixed pulley reduce the force you need to lift the engine? What if you added one movable pulley to the system?
How close was your prediction?
The hook at the start of this lesson quoted Archimedes: "Give me a lever long enough and a fulcrum on which to place it, and I shall move the world." Is that physically possible? Actually, yes — in theory! But there's a catch.
Explain why Archimedes was right in principle but why it would still be impossibly impractical. Use the words mechanical advantage, force and distance at least once each, and explain the force–distance trade-off.
Q1. Draw a labelled diagram of a Class 1 lever. Identify the fulcrum, effort and load, and explain how it provides mechanical advantage. (3 marks)
Q2. A builder uses a block and tackle (2 movable pulleys) to lift a 400 N steel beam. If the mechanical advantage is 4, what force does the builder need to apply? Explain how the pulley system achieves this. (3 marks)
Q3. Choose any three simple machines you can find in an Australian school. For each, identify the type of simple machine, the effort, load and fulcrum (or equivalent), and estimate whether MA > 1, < 1 or = 1. (5 marks)
Answers
▾MCQ 1
C — Mechanical advantage = output force ÷ input force. It is not always >1 or <1; it depends on the machine configuration. Class 3 levers have MA <1.
MCQ 2
B — In a Class 2 lever the load is between the fulcrum and the effort (wheelbarrow: wheel = fulcrum, load in tray = load, handles = effort). This always gives MA > 1.
MCQ 3
B — A fixed pulley is attached to a ceiling or beam and only changes the direction of force (you pull down instead of up). It has MA = 1. A movable pulley attached to the load actually reduces force needed.
MCQ 4
C — Simple machines can change force direction, reduce force needed, and increase distance over which force is applied — but they can NEVER create energy from nothing (that would violate conservation of energy).
MCQ 5
C — Tweezers are a Class 3 lever: the fulcrum is at the joined end, the effort (where you squeeze) is between the fulcrum and the load (what you pick up). Seesaw = Class 1; wheelbarrow and bottle opener = Class 2.
Short Answer 1
Model answer: A Class 1 lever has the fulcrum between the effort and the load (e.g. a seesaw or crowbar). [Diagram: F at centre, E on one side, L on the other.] By placing the fulcrum closer to the load and farther from the effort, a small effort force over a large distance can lift a heavy load over a small distance. This is mechanical advantage: output force > input force.
Short Answer 2
Model answer: Force = Load ÷ MA = 400 N ÷ 4 = 100 N. The block-and-tackle uses multiple rope segments supporting the load — with 4 segments, each carries ¼ of the total load weight. The trade-off is that the builder must pull the rope 4 times farther than the beam rises, so the total energy input is still equal to 400 N × height lifted.
Short Answer 3
Example model answer: (1) Door handle — wheel and axle; effort = hand turning the handle (wheel); load = latch bolt; axle = door spindle; MA > 1 (handle radius > spindle radius). (2) Scissors — Class 1 lever; effort = hand squeezing; fulcrum = pivot screw; load = paper; MA can be > or < 1 depending on where you cut. (3) Stapler — Class 2 lever; fulcrum at far end; effort at top; load = staple being driven; MA > 1. (Award 1 mark per correct machine up to 3, plus 1 mark for MA reasoning, plus 1 mark overall clarity.)