Mechanical Comprehension (MC)
Mechanical Comprehension (MC) is applied physics — how machines and forces work. Most questions come with a diagram of a mechanism you have to reason about. It needs understanding, not heavy math.
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Simple machines
Levers (three classes; mechanical advantage = effort arm ÷ load arm, so a longer effort arm needs less force); pulleys (a fixed pulley only changes direction, giving a mechanical advantage of 1; each supporting rope in a movable/compound system adds to the advantage); plus inclined planes, wedges, screws and the wheel-and-axle, which trade distance for force.
Gears
Gear speed is inversely proportional to the number of teeth — a small gear driving a large one turns the large one slower but with more torque. Meshed gears spin in opposite directions; an idler gear between two gears makes them turn the same way.
Force, work and balance
Work = force × distance (a machine never reduces total work — it trades force for distance). Torque = force × distance from the pivot; balance a beam or seesaw with equal moments on each side. A support closer to a load carries more of it.
Fluids and materials
Pressure = force ÷ area; Pascal's principle means a larger piston produces a greater output force in a hydraulic system. Know friction, density and buoyancy, and center of gravity/stability.
Key takeaways
- Simple machines (levers, pulleys, gears) are the biggest block.
- Fixed pulley = MA 1 (direction only); movable pulleys multiply force.
- Balance problems: effort × its arm = load × its arm.
Start a free Mechanical Comprehension practice set — timed, with a worked explanation after every question.
Go to Mechanical Comprehension practiceFree sample Mechanical Comprehension questions
A few sample questions with worked answers. Our free Mechanical Comprehension practice set has 268 questions in total — every one with a full explanation.
- A.Rise to the same level in all of them ✓
- B.Stay only in the first container
- C.Be highest in the widest container
- D.Be highest in the narrowest container
- A.240 lb ✓
- B.60 lb
- C.15 lb
- D.180 lb
- A.40 lb
- B.16 lb ✓
- C.20 lb
- D.160 lb
- A.in opposite directions ✓
- B.in the same direction
- C.in no direction
- D.in random directions
- A.second-class lever ✓
- B.pulley
- C.first-class lever
- D.third-class lever
Mechanical Comprehension cheat sheet
The formulas and facts worth memorising for this subtest. See all ASVAB cheat sheets →
- Mechanical advantage = output ÷ input force = effort arm ÷ load arm (lever)
- Balance a lever/seesaw: effort × its arm = load × its arm
- Fixed pulley: MA = 1 (direction only); each supporting rope in a movable system adds to the MA
- Gears: speed ∝ 1 ÷ number of teeth (bigger gear = slower, more torque); meshed gears turn opposite ways
- Work = force × distance (a machine trades force for distance, not total work)
- Pressure = force ÷ area; hydraulics/Pascal: a bigger piston gives more output force
- Buoyancy: upward force = weight of displaced fluid (water ≈ 62.4 lb/ft³)
- Center of gravity: extending a load shifts it; a wider, lower base is more stable