Physical reasoning about machines, forces, fluids and structures.
Mechanical Comprehension measures your understanding of mechanical and physical principles applied to everyday situations: levers, gears, pulleys, inclined planes, friction, pressure, buoyancy, and how structures carry loads. Items often come with a simple diagram of a machine or a physical setup, and you choose the answer that follows from the mechanics.
This is a reasoning section rather than a formula section. You will rarely need to compute; you need to know what a machine does to force and distance, how pressure behaves in a fluid, and which way an object moves when forces are unbalanced. The most common failure is answering from intuition about how things feel rather than from the principle.
MC is not part of the AFQT, but it is one of the most valuable subtests for mechanical and maintenance jobs, and the line scores that use it are the reason many candidates study it even though it cannot affect eligibility itself.
Section 9 of 10 in our timed mock template. This subtest is not part of the AFQT; it feeds service component and line scores used for job qualification.
The shapes below are what our bank is written against, and what the section is built around. None of them are reproduced from the official test.
Specific, not generic: what the items in this topic test, and the one or two moves that solve most of them.
An object moves in the direction of the net force, and it keeps moving without a force once it is going - the everyday intuition that things naturally slow down is friction, not a law. Heavier objects have more inertia. Friction opposes motion and increases with how hard surfaces are pressed together, and it is largely independent of contact area, which surprises most test-takers.
12 original questions in this topic set.
Every machine trades force for distance. Mechanical advantage is output force over input force; a lever multiplies force when the effort arm is longer than the load arm, an inclined plane reduces the force needed by increasing the distance travelled, and a single fixed pulley changes only direction with no advantage at all. That last one is the most-tested exception, so know it cold.
12 original questions in this topic set.
Meshed gears turn in opposite directions, and speed is inversely proportional to tooth count: a 10-tooth driver turning a 30-tooth gear makes the large gear spin at a third of the speed with three times the torque. A belt connecting two pulleys makes them turn the same way, with speed inversely proportional to diameter. For block-and-tackle, count the rope segments actually supporting the load to get the ideal advantage.
12 original questions in this topic set.
Pressure in a static fluid depends on depth and density, not on the shape or width of the container, which is why a narrow deep column can exert more pressure than a wide shallow one. Buoyancy equals the weight of displaced fluid - a floating object displaces its own weight - so whether something sinks depends on density relative to the fluid. In flowing fluid, faster movement means lower pressure, and a constriction speeds the flow up. Hydraulics transmit pressure undiminished, so a small piston over a small area moves a large piston over a large area with multiplied force and reduced travel.
12 original questions in this topic set.
Triangles are rigid; rectangles rack. Loads create compression, tension, bending and torsion, and the strongest arrangement puts material where the stress is greatest. For stability, a lower centre of gravity and a wider base both help, and a tall narrow object topples when its centre of gravity moves outside its base.
12 original questions in this topic set.
Sampled from the Mechanical Comprehension bank below, spread across its topics so you can see the range. The correct option is marked, the method is written out, and the tempting wrong options are explained - the same format you get in the app the moment you answer.
A book lying on a level desk stays there, and a puck sliding on frictionless ice keeps its speed and heading. What is required to change either object's motion?
Newton's first law states that velocity changes only when an unbalanced external force acts, so with zero net force an object at rest stays at rest and a moving object continues in a straight line at constant speed.
Which simple machine is essentially an inclined plane wound around a cylinder?
A screw thread is a ramp wrapped into a helix: each turn drives the load forward by the pitch while the effort travels the whole length of the circle.
An open (uncrossed) belt connects a 5 cm driving pulley to a 15 cm pulley. How does the large pulley turn?
Both pulleys ride the same belt speed, so turning rate varies inversely with diameter: 5 / 15 = 1/3, and an uncrossed belt does not reverse direction.
Which property of a liquid describes how strongly it resists flowing?
Viscosity is internal friction between moving layers of fluid; honey and oil have high viscosity, water low, and both flow far more easily when warmed.
On the clock
MC is 16 items in 20 minutes on our template - about 75 seconds each, the second-most generous pacing on the test after Arithmetic Reasoning. Use the time to sketch; MC is where rushing costs the most.
Free Mechanical Comprehension practice on this site, graded instantly with explanations. Timed sections, wrong-answer review and the full library are in the app.