Levers, Linkages, Cams and Followers
Mechanisms change the size, direction and type of movement - and this topic carries most of the exam's calculation marks. Master mechanical advantage, velocity ratio and gear ratios with worked examples.
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Mechanisms do the maths ⚙️
A **mechanism** changes movement: its **size**, its **direction**, or its **type** (turning a motor's spin into a straight push, say). Levers, linkages, cams, pulleys and gears are the building blocks. This is also the topic that carries **most of the exam's calculation marks**, so alongside naming parts you will practise the three formulae that come up again and again: **mechanical advantage**, **velocity ratio** and **gear ratio**.
Four types of motion 🔄
Every mechanism turns one type of motion into another. Learn the four exact names.
Match each motion to an example 🔗
- Linear
- Reciprocating
- Rotary
- Oscillating
- A lift moving straight up a shaft
- A piston moving back and forth in a cylinder
- A wheel spinning on an axle
- A pendulum swinging side to side
Class 1 levers ⚖️
In a class 1 lever, such as a seesaw, what sits between the effort and the load? (The fulcrum is the pivot point.)
- The fulcrum
- The load
- The effort
- Nothing - all three are at the same point
The three formulae 🧮
Learn these exactly - most of the calculation marks depend on them: - **Mechanical advantage (MA) = load / effort** (a ratio of forces, no units).\n- **Velocity ratio (VR) = distance moved by effort / distance moved by load** (a ratio of distances).\n- **Efficiency = (MA / VR) x 100%**.\n- For gears and pulleys, **ratio = driven / driver** (teeth or diameter). Always **show your working**: write the formula, substitute the numbers, then give the answer.
Calculate mechanical advantage ➗
An interactive activity.
Mechanical advantage vs velocity ratio 🆚
This is the confusion examiners see most. MA and VR are both ratios, but of completely different things.
Force or distance? 🎯
Which quantity is a ratio of distances or gear teeth, rather than a ratio of forces?
- Velocity ratio
- Mechanical advantage
- The load
- The effort
Match each component to its job 🧩
- Bell crank
- Idler gear
- Bevel gear
- Rack and pinion
- Changes the direction of a force through an angle
- Reverses the direction of rotation without changing the overall ratio
- Transfers drive between shafts at an angle, changing the plane of rotation
- Converts rotary motion into straight-line linear motion
Calculate the gear ratio 🔢
An interactive activity.
Calculate the output speed 📈
An interactive activity.
Design the drive 🧭
An interactive activity.
Show your working ✍️
An interactive activity.
The grade-9 habit 🌟
Two habits win the calculation marks here. First, **keep MA and VR separate in your head**: MA is **load / effort** (forces), VR is a ratio of **distances or teeth**. Muddling them is the single most common error. Second, for gears always reason from **driven over driver**: more teeth on the **driven** gear means a **slower** output shaft but **more torque**, and an **idler** gear only flips the direction, never the ratio. Write the formula, substitute, then answer with the right unit - method marks are there even if the final number slips.