Mechanical / Spatial Reasoning
This section tests physical intuition and mental rotation: gears, pulleys, levers, moments, and folding or rotating 3D shapes. No specialist physics is required, but basic principles must be applied accurately.
Principles
- Meshing gears turn in opposite directions; an open belt or chain drive turns pulleys in the same direction.
- Gear ratio equals teeth ratio; a larger gear turns more slowly with greater torque.
- A fixed pulley changes direction but gives no force advantage. A movable pulley halves the ideal effort.
- Lever: moment = force × perpendicular distance from the fulcrum. Balance when moments are equal.
- Nets: opposite faces of a cube never touch; track a marked face by folding edges systematically.
Worked example: a lever has a 30 N load 2 m from the fulcrum. How much effort is needed at 3 m on the other side? Load moment = 30 × 2 = 60 N·m. Effort × 3 = 60, so effort = 20 N. The longer arm gives mechanical advantage; the trap is using the load’s distance for the effort.
Traps that cost marks
- Assuming a fixed pulley reduces the force needed.
- Forgetting that meshing gears reverse direction.
- Using total lever length instead of distance from the fulcrum.
- Losing track of a face during net folding.
- Ignoring that a crossed belt reverses direction.