Gears, Levers, and Pulleys: A Guide to Mechanical Reasoning

Mechanical reasoning is the ability to understand and apply basic principles of physics and mechanics. It's a test of your intuitive grasp of how physical objects and systems interact. These tests are commonly used in hiring for technical, engineering, and skilled trade roles, as they predict a person's aptitude for working with machinery and equipment. This guide will introduce you to the core concepts found in mechanical reasoning tests, including levers, gears, pulleys, and simple circuits, providing you with the knowledge to solve these visual physics puzzles.

1. Levers and Fulcrums

A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. The key principle is balancing torque (rotational force).

Formula: Force1 x Distance1 = Force2 x Distance2

This means a smaller force can lift a heavier weight if it is applied further away from the fulcrum. In a typical problem, you might be shown a seesaw with different weights at different distances and asked which way it will tilt. To solve, calculate the torque on each side (Force x Distance). The side with the greater torque will go down.

2. Gears and Cogs

Gears are wheels with teeth that mesh together. Understanding their interaction is crucial.

Direction of Rotation: When two gears mesh directly, they always rotate in opposite directions. If one turns clockwise, the one it's touching turns counter-clockwise. An odd number of gears in a chain means the first and last gears turn in the same direction. An even number means they turn in opposite directions.
Speed of Rotation: The speed of a gear is inversely proportional to its size (or number of teeth). A small gear will rotate faster than a large gear it is driving. If a 20-tooth gear drives a 40-tooth gear, the large gear will rotate at half the speed of the small one.

3. Pulleys and Belts

Pulleys are wheels on an axle or shaft that are designed to support movement and change of direction of a taut cable or belt.

Direction: If two pulleys are connected by a simple, un-crossed belt, they will rotate in the same direction. If the belt is crossed (in a figure-8 shape), they will rotate in opposite directions.
Mechanical Advantage: Complex pulley systems can reduce the amount of force needed to lift a heavy object. The mechanical advantage is generally equal to the number of rope segments supporting the load. If a 100kg weight is supported by 4 rope segments in a pulley system, the effort required to lift it is reduced to approximately 25kg.

4. Springs and Pressure

These questions test your understanding of pressure and tension.

Springs: A weight hanging on a spring will cause it to extend. Two identical springs supporting a weight side-by-side will each take half the load and extend less than a single spring would. Two springs in a series (one below the other) will both experience the full weight and the total extension will be greater.
Fluid Dynamics (Pressure): Pressure in a liquid is exerted equally in all directions. In a U-shaped tube, the liquid will be at the same level on both sides, regardless of the shape of the tube. If pressure is applied to an enclosed fluid (hydraulics), that pressure is transmitted to all parts of the fluid. This is how a small force on a small piston can generate a large force on a large piston.

Mechanical reasoning questions are about visualizing forces and movements. When you see a problem, try to mentally animate it. Trace the path of force from the input to the output. By understanding these core principles, you can systematically analyze and solve these practical physics challenges.