How do levers and linkages give a mechanical advantage, and how are moments calculated?
Levers and linkages: the three classes of lever, the principle of moments, mechanical advantage, and linkages that change the direction of motion.
A CCEA GCSE Technology and Design answer on levers and linkages: the three classes of lever, the principle of moments with the equation moment equals force times distance, mechanical advantage, and linkages that change the direction or size of a motion.
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What this dot point is asking
CCEA wants you to know the three classes of lever, the principle of moments (with the equation moment = force x distance), the idea of mechanical advantage, and how linkages change the direction or size of a motion. Levers are the simplest force-multiplying mechanism.
The answer
Levers and the three classes
A lever is a rigid bar that turns about a fixed point called the pivot (fulcrum). It has an effort (the force you apply) and a load (the force it moves). The class depends on the order of these along the bar.
A memory aid is "1-2-3 = pivot, load, effort in the middle": for a first-class lever the pivot is in the middle, for second-class the load, for third-class the effort.
The principle of moments
This is the equation you use to find an unknown force or distance on a balanced lever.
Mechanical advantage
A wheelbarrow and a bottle opener have a large mechanical advantage, letting a small effort move a large load. A third-class lever has an MA less than 1 (the effort is larger than the load) but gains speed and range of movement instead, which is why tweezers and the forearm are third class.
Linkages
Worked example: a balanced lever calculation
Examples in context
- Example 1. A wheelbarrow
- A second-class lever: the load (the barrow) sits between the wheel (pivot) and the handles (effort), giving a large mechanical advantage so a heavy load is lifted easily.
- Example 2. Scissors
- A first-class lever (two of them): the pivot is between the handles (effort) and the blades (load); long handles give more cutting force.
- Example 3. A folding clothes airer
- A linkage of pivoted bars lets the whole frame fold flat and open out, changing and guiding the motion of every arm together.
Being able to identify the lever class, calculate with moments, and find mechanical advantage lets you answer both the naming questions and the calculation questions CCEA sets.
Try this
Q1. Which class of lever has the pivot between the effort and the load? [1 mark]
- Cue. A first-class lever.
Q2. State the equation for a moment. [1 mark]
- Cue. Moment = force x perpendicular distance from the pivot.
Q3. A force of 40 N acts 0.3 m from a pivot. Calculate the moment. [2 marks]
- Cue. .
Q4. A lever balances a 100 N load with a 25 N effort. Calculate the mechanical advantage. [2 marks]
- Cue. .
Q5. Give one use of a reverse-motion linkage. [1 mark]
- Cue. Changing the direction of a motion (e.g. so an output moves opposite to the input), as in some toys and mechanisms.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksA lever has an effort of 20 N applied 0.6 m from the pivot. Calculate the load it can balance 0.2 m from the pivot on the other side.Show worked answer →
Use the principle of moments: for balance, clockwise moment equals anticlockwise moment (1).
Effort moment (1).
Load , so load (1).
So the lever balances a 60 N load, showing the lever gives a mechanical advantage of 3 (1).
CCEA style3 marksName the three classes of lever and give one example of each.Show worked answer →
First class: pivot between effort and load, e.g. a see-saw or a pair of scissors (1).
Second class: load between pivot and effort, e.g. a wheelbarrow or a bottle opener (1).
Third class: effort between pivot and load, e.g. tweezers or a fishing rod (1).
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Sources & how we know this
- CCEA GCSE Technology and Design specification — CCEA (2017)