Mechanical Comprehension
What is being tested
Mechanical comprehension asks you to predict how simple physical systems behave: levers, pulleys, gears, inclined planes, and basic force and motion. You do not need advanced physics - you need clear mental models.
Concepts to master
- Levers: moment = force × distance from the pivot. Balance occurs when moments on each side are equal.
- Pulleys: a single fixed pulley changes direction only; movable pulleys and multiple supporting rope sections reduce the effort needed.
- Gears: meshed gears turn in opposite directions; a larger gear turns more slowly than a smaller one it drives.
- Inclined planes and wedges: a gentler slope needs less force but over a longer distance.
- Friction and stability: lower centre of gravity and wider base mean greater stability.
- Pressure: force spread over area; smaller area gives greater pressure for the same force.
Traps
Questions often swap 'force' and 'distance' - a machine may reduce force while increasing the distance moved. Direction questions (which way does the gear turn?) trip candidates who forget that meshed gears reverse. Watch for 'effort' vs. 'load' labels and for diagrams where the pivot is not where you assume.
Rule of thumb
For any lever or balance question, compute force × distance on each side of the pivot and compare the two products.
Worked example
A lever has a pivot with a 20 N load 0.5 m from it. How much effort is needed 1.0 m from the pivot on the other side? Moments balance: 20 × 0.5 = effort × 1.0, so effort = 10 N. The lever halves the force but the effort end moves twice as far - energy is conserved, not multiplied.