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How do levers and linkages change forces and motion, and what is mechanical advantage?

Levers and the three lever classes, mechanical advantage and the law of the lever, types of motion (linear, rotary, reciprocating, oscillating), linkages (reverse, parallel, bell crank) and how mechanisms change the size, direction and type of a force or motion.

A focused answer to Eduqas A-Level Product Design on mechanisms, levers and linkages: the three lever classes, mechanical advantage and the law of the lever, the four types of motion, and reverse, parallel and bell crank linkages, with a worked mechanical advantage calculation.

Generated by Claude Opus 4.812 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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Quick answer

A lever turns about a pivot (fulcrum) and changes a force or movement. The class depends on the order of effort, load and pivot: first class has the pivot in the middle (seesaw, pliers); second class has the load in the middle (wheelbarrow, nutcracker) and always multiplies force; third class has the effort in the middle (tweezers, forearm) and multiplies movement at the cost of force. Mechanical advantage is how much a mechanism multiplies force: $MA = \frac{\text{load}}{\text{effort}} = \frac{\text{effort distance}}{\text{load distance}}$ (no units). The law of the lever says effort times its distance equals load times its distance at balance. The four types of motion are linear, rotary, reciprocating and oscillating. Linkages (reverse motion, parallel, bell crank) change the direction or type of motion.

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What this dot point is asking
Levers and the three classes
Mechanical advantage and the law of the lever
Types of motion
Linkages

What this dot point is asking

Eduqas wants you to know the three lever classes, calculate mechanical advantage and apply the law of the lever, identify the four types of motion, and understand linkages that change the size, direction or type of a force or motion. Mechanisms are how products move and how forces are changed, combining technical knowledge with the applied maths of mechanical advantage, so they are examined as recall, a calculation and applied reasoning.

Levers and the three classes

Key fact

A lever is a rigid bar that turns about a pivot (fulcrum) to change the size, direction or distance of a force. The three classes are defined by the order of the effort (E), the load (L) and the pivot (P). First class: pivot in the middle (E-P-L), like a seesaw, scissors or pliers; it reverses direction and can give a mechanical advantage above or below one depending on the arm lengths. Second class: load in the middle (P-L-E), like a wheelbarrow, nutcracker or bottle opener; the effort arm is always longer, so it always multiplies force (mechanical advantage greater than one). Third class: effort in the middle (P-E-L), like tweezers, a fishing rod or the human forearm; the load arm is longer, so it multiplies movement and speed but needs more effort than the load (mechanical advantage less than one).

Mechanical advantage and the law of the lever

Definition

Mechanical advantage (MA) measures how much a mechanism multiplies force: it is the load divided by the effort, or equivalently the effort arm divided by the load arm, $MA = \frac{\text{load}}{\text{effort}} = \frac{\text{effort distance}}{\text{load distance}}$ . It has no units. An MA greater than one means the mechanism multiplies force (you lift a big load with a small effort); an MA less than one means it multiplies movement (a small movement of the load needs a larger movement of the effort, as in third-class levers). The law of the lever (the principle of moments) states that at balance, effort times effort distance equals load times load distance: $E \times d_E = L \times d_L$ . This lets a designer size a lever to lift a known load with an available effort.

Types of motion

Linkages

Calculating mechanical advantage of a lever

Identify effort, load and distances

A bottle opener is a second-class lever: the pivot is at the cap edge, the cap (load) is close to the pivot at $0.02$ m, and the hand (effort) is at $0.12$ m from the pivot.

Find the mechanical advantage from the arms

Mechanical advantage is the effort distance divided by the load distance: $MA = \frac{0.12}{0.02} = 6$ (no units). The opener multiplies the hand force six times.

Use the law of the lever to find the effort

If the cap needs a load of $90$ N to lift it, the effort required is $E = \frac{L}{MA} = \frac{90}{6} = 15$ N, so a gentle $15$ N pull opens it. (Equivalently $E \times d_E = L \times d_L$ gives $E \times 0.12 = 90 \times 0.02$ .)

State the design point

Conclude that the second-class lever multiplies force (MA of 6), so a small effort opens a stiff cap, and that moving the hand further out (a longer handle) increases the MA further. State that MA has no units and that load equals MA times effort, which is the relationship the marks reward.

Exam-style practice questions

Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Eduqas 20204 marksA lever has an effort applied 0.60 m from the pivot and lifts a load 0.15 m from the pivot. Calculate the mechanical advantage, and state what this tells you about the effort needed.

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A Component 1 mechanical advantage calculation. Marks for the method and the interpretation.

Mechanical advantage from the lever arms is the effort distance divided by the load distance: $MA = \frac{0.60}{0.15} = 4$ . A mechanical advantage of 4 (which has no units) means the lever multiplies the effort four times, so the effort needed is a quarter of the load: a 200 N load could be lifted with about 50 N of effort.

Award marks for the correct ratio and the interpretation that the effort is multiplied (load equals MA times effort, so effort equals load divided by MA). A common dropped mark is inverting the ratio or giving MA a unit.

Eduqas 20216 marksDiscuss the three classes of lever, giving a product example of each, and explain how the class affects the mechanical advantage. Refer to the position of the effort, load and pivot.

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A Component 1 extended question marked by levels of response. Reward the three classes, examples and the effect on mechanical advantage.

First class: pivot between effort and load (a seesaw, scissors, pliers); can give a mechanical advantage greater or less than one depending on arm lengths. Second class: load between pivot and effort (a wheelbarrow, a nutcracker, a bottle opener); always gives a mechanical advantage greater than one, so it multiplies force. Third class: effort between pivot and load (tweezers, a fishing rod, the human forearm); gives a mechanical advantage less than one, so it multiplies movement and speed at the cost of force.

A top answer names the classes by the order of effort, load and pivot, gives a product for each, and explains that second class multiplies force while third class multiplies movement, reaching a clear conclusion about choosing the class for the job.

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Sources & how we know this

Eduqas A Level Design and Technology specification (Product Design) — Eduqas (2017)