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Summaries · Grade 7 Technology › Levers, pulleys and mechanical advantage
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Levers, pulleys and mechanical advantage

The three classes of lever, mechanical advantage, cranks and pulleys. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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Three classes of lever

Class 1: fulcrum in the middlescissors, see-sawClass 2: load in the middlewheelbarrow, bottle openerClass 3: effort in the middlefishing rod, tweezersfulcrumloadeffort
Always ask: what is in the middle?

A class 3 lever (fishing rod) needs more effort than the load. So why use it? The load moves further and faster.

Levers and pulleys make heavy work lighter.
Levers and pulleys make heavy work lighter.
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Mechanical advantage and pulleys

Load÷Effort=MA
MA tells you how many times a machine multiplies your effort.
100 N100 N100 N± 50 NFixed pulley:direction onlyMovable pulley:about half the effort
A fixed pulley at the top of a flagpole; a movable pulley moves with the load.
  • A crank is an arm with a handle that turns a shaft round.
  • A building crane uses pulleys, a lever arm and a counterweight.
Rule

Load = MA × effort.   Effort = load ÷ MA.   MA = load ÷ effort.

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Linked levers around us

ClassLinked examples
Class 1 (fulcrum in the middle)Scissors, pliers, hedge shears
Class 2 (load in the middle)Office punch, nutcracker
Class 3 (effort in the middle)Stapler, tweezers
Rule

A linkage with more than one pivot can send movement and force in a different direction.

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Remember this and test yourself

Remember this: your summary
  • Class 1: fulcrum in the middle. Class 2: load in the middle. Class 3: effort in the middle.
  • Mechanical advantage = load ÷ effort. 600 N ÷ 200 N = 3.
  • MA of 4 and you push with 50 N: load = 4 × 50 = 200 N. MA of 1: effort = load.
  • Fixed pulley: changes direction only. Movable pulley: roughly halves the effort.
  • Block and tackle with 4 ropes: 400 N load ≈ 100 N effort, but you pull much more rope through.

Write these points in your book. Read them again the night before the test.

Memory trick

1-2-3 = F-L-E: class 1 Fulcrum, class 2 Load, class 3 Effort in the middle.

Flash cards · Tap to turn over

Important words

First say what the word means, then turn the card over.

Test yourself · Part 2

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