Mechanical Comprehension
What is tested
Mechanical Comprehension tests levers, pulleys, gears, incline planes, pressure, buoyancy, and basic machines. The exam favors qualitative reasoning and simple mechanical advantage over memorized formulas.
Core rules
- Lever: mechanical advantage = effort arm ÷ load arm. Balance: effort × effort arm = load × load arm.
- Pulley: count rope segments supporting the movable load; a fixed pulley changes direction only.
- Gears: meshing gears turn in opposite directions; speed ratio is inverse to tooth count.
- Pressure in a fluid = density × gravity × depth; it acts in all directions and depends on depth, not container shape.
- Buoyancy equals the weight of displaced fluid. An object floats if its average density is less than the fluid's.
Worked example
A lever has a 2.0 m effort arm and a 0.5 m load arm. What effort lifts a 200 N load? Mechanical advantage = 2.0 ÷ 0.5 = 4. Required effort = 200 ÷ 4 = 50 N. The trade-off is distance: the effort end moves four times farther than the load.
Traps that cost marks
Counting the rope segment you pull; forgetting friction; assuming a bigger object always sinks; and confusing pressure with total force. In gear questions, read whether the question asks for direction, speed, or torque.