Mechanical Reasoning
What this domain measures
Mechanical reasoning items test intuitive physics rather than memorised formulas: levers, pulleys, gears, wheels and axles, pressure and force, fluid behaviour, and basic tool and machine principles. Most questions show a described or drawn setup in words and ask which way something moves, which side carries more force, or what happens when one part changes.
Core rules
- Levers: mechanical advantage equals effort arm length divided by load arm length, measured from the fulcrum. A longer effort arm lets a smaller effort lift a larger load.
- Pulleys: a single fixed pulley changes direction only, with no force advantage. Movable pulleys that share the load across multiple rope segments reduce the effort by roughly the number of supporting segments.
- Gears: meshed gears turn in opposite directions. The gear ratio is set by tooth counts, so a small gear driving a large gear slows the output and increases turning force.
- Pressure equals force divided by area. The same force spread over a larger area gives lower pressure; a smaller nozzle or piston area raises pressure.
- Fluids flow from higher pressure to lower pressure, and flow increases with a greater pressure difference or a wider opening.
- Friction and balance: an object at rest on a slope stays put when friction offsets the downhill component of its weight.
Worked example
A lever has its fulcrum 2 feet from a load of unknown weight and 6 feet from the point where 50 pounds of effort is applied. What load can be lifted?
Step 1 - mechanical advantage equals effort arm divided by load arm: 6 divided by 2 equals 3. Step 2 - load equals effort times mechanical advantage: 50 times 3 equals 150 pounds. Check - the effort moves three times as far as the load, so the force is multiplied by three, which is consistent with conservation of work.
Traps that cost marks
- Measuring lever arms from the end of the bar instead of from the fulcrum.
- Assuming any pulley gives a force advantage; a fixed pulley only redirects.
- Forgetting that meshed gears reverse rotation direction.
- Confusing force with pressure when area changes.
- Choosing the answer that feels strong rather than the one the ratio produces.