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How do mechanisms change the type, direction and size of motion in a product?

Mechanical devices that transmit and convert motion, including the four types of motion (linear, rotary, reciprocating, oscillating), levers and the three classes of lever, linkages that change direction or magnitude of movement, cams and followers that convert rotary to reciprocating motion, and how mechanisms are selected to produce a required movement in a product.

A focused answer to the Edexcel 9DT0 content on mechanical devices, covering the four types of motion, the three classes of lever, linkages that change direction or magnitude of movement, and cams and followers that convert rotary to reciprocating motion.

Generated by Claude Opus 4.813 min answerUpdated 2026-06-02

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Quick answer

Mechanisms change the type, direction or size of motion. The four types of motion are linear (straight line), rotary (turning), reciprocating (back and forth in a line) and oscillating (swinging to and fro about a pivot). Levers pivot about a fulcrum to change force and movement; the three classes are set by the order of fulcrum, load and effort (first class: fulcrum in the middle, like a seesaw; second class: load in the middle, like a wheelbarrow, giving force advantage; third class: effort in the middle, like tweezers, giving movement advantage). Linkages connect parts to change the direction or magnitude of motion (a reverse-motion linkage flips direction). A cam and follower converts rotary motion into reciprocating or oscillating motion, with the cam profile shaping the rise, dwell and fall.

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What this dot point is asking

Edexcel wants you to know the mechanical devices that transmit and convert motion: the four types of motion, the three classes of lever, linkages that change the direction or size of movement, and cams and followers that convert rotary to reciprocating motion, and to select a mechanism to produce a required movement.

The answer

The four types of motion

Levers and the three classes

Linkages

A linkage joins rigid links with pivots to change the direction or magnitude of motion. A reverse-motion linkage makes the output move opposite to the input; a bell crank changes the direction of motion through an angle (for example 90 degrees); a push-pull (parallel) linkage keeps two parts moving together. Linkages are used in folding products, controls and toys.

Cams and followers

A cam is a shaped rotating part; a follower rests on its edge and moves as the cam turns, converting rotary motion into reciprocating or oscillating motion. The cam profile controls the movement: a pear cam gives a dwell (follower stays still) then a rise and fall; an eccentric (off-centre circle) gives smooth continuous rise and fall; a snail (drop) cam gives a gradual rise then a sudden drop (and works in only one direction).

Effort needed on a second-class lever

A wheelbarrow carries a $600$ N load whose centre is $0.40$ m from the wheel (fulcrum). The handles are $1.2$ m from the wheel. Find the effort needed to lift it.

step 1: Apply the lever law

$\text{effort} \times \text{effort arm} = \text{load} \times \text{load arm}$ , so $\text{effort} \times 1.2 = 600 \times 0.40$ .

step 2: Solve for the effort

$\text{effort} = \dfrac{600 \times 0.40}{1.2} = \dfrac{240}{1.2} = 200$ N.

step 3: Find the mechanical advantage

$\text{MA} = \dfrac{600}{200} = 3$ , so the wheelbarrow lets a $200$ N effort lift a $600$ N load, a force advantage of $3$ .

Examples in context

A wheelbarrow and a bottle opener are second-class levers that multiply force, while scissors are a first-class lever and tweezers a third-class lever that trades force for movement and control. Folding pushchairs and desk lamps use linkages to change the direction of motion and keep parts parallel. Cams appear throughout products: the camshaft in an engine opens the valves, a cam in a mechanical toy or automaton lifts and drops a figure, and an eccentric drives a smooth reciprocating action. Selecting the right mechanism, and using the lever law to size the effort or find the mechanical advantage, are the core skills Edexcel tests here.

Try this

Q1. State the four types of motion. [2 marks]

Cue. Linear, rotary, reciprocating and oscillating.

Q2. A first-class lever has the load $0.20$ m from the fulcrum and the effort $0.80$ m from the fulcrum. What effort balances a $400$ N load? [2 marks]

Cue. $\text{effort} = \dfrac{400 \times 0.20}{0.80} = 100$ N.

Q3. Explain what a cam and follower mechanism does. [2 marks]

Cue. It converts the rotary motion of the shaped cam into reciprocating (or oscillating) motion of the follower, with the cam profile setting the pattern of rise, dwell and fall.

Exam-style practice questions

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

Edexcel 20194 marksA wheelbarrow is an example of a second-class lever. Explain what this means and the advantage it gives.

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Award marks for the arrangement of load, effort and fulcrum and for the advantage.

In a second-class lever the load is between the fulcrum and the effort. In a wheelbarrow the fulcrum is the wheel, the load (the contents) sits in the barrow between the wheel and the handles, and the effort is applied at the handles.

Because the effort is further from the fulcrum than the load, the effort arm is longer than the load arm, giving a mechanical advantage greater than 1, so a smaller effort lifts a larger load. Markers reward correctly placing load between fulcrum and effort and explaining the mechanical advantage (force multiplied because the effort arm is longer).

Edexcel 20216 marksExplain how a cam and follower mechanism works and how the cam profile controls the movement, using an example.

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Extended-response item marked on levels (correct mechanism, role of the profile and a sensible example).

A cam is a specially shaped rotating component; as it turns, a follower resting on its edge rises and falls, converting the cam's rotary motion into reciprocating (up and down) or oscillating motion of the follower.

The cam profile (its shape) controls the movement: the radius at each angle sets the follower height, so a pear-shaped cam gives a dwell (the follower stays still over the round part) then a rise and fall; an eccentric (off-centre circle) gives smooth continuous rise and fall; a snail (drop) cam gives a gradual rise then a sudden drop. The amount of rise depends on the difference between the largest and smallest radius.

Example: in an engine, cams on the camshaft open and close the valves; in an automaton, a cam lifts a figure. A strong answer links rotary input to reciprocating output and explains how the chosen profile shapes the motion (dwell, rise, fall), with an example.

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Sources & how we know this

Pearson Edexcel A-Level Design and Technology: Product Design (9DT0) specification — Pearson Edexcel (2017)