SIFT Mechanical Comprehension: Gears, Levers and Pulleys
The Mechanical Comprehension Test (MCT) is computer-adaptive and runs 15 minutes; the number of questions varies by examinee (SIFT FAQ V2.0). It covers how simple machines, fluids and basic electricity behave.
Most questions reduce to a handful of rules you can learn in an evening and apply in under a minute each. Try five below.
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Format and timing
| Mechanical Comprehension (MCT) | |
|---|---|
| Questions | varies (computer-adaptive) |
| Time limit | 15 minutes |
| Scoring | adaptive; too few answered brings a penalty |
| Our timed set | 20 questions in 15 minutes (our length) |
Source: SIFT FAQ V2.0. The 20-question length is ours; the real test adapts to you.
Scoring on an adaptive subtest
Each question is chosen from your earlier answers, so two candidates can see different numbers of questions at different difficulty. Answer too few before the 15 minutes run out and a penalty may be applied; guess randomly at the end and you'll usually do worse. Plan on no skipping and no going back.
Your MCT result goes into the one SIFT score (20–80; 40 qualifies for Army aviation), combined through a proprietary, compensatory formula. Any SIFT score in our app is an estimate.
What it tests
Physical intuition plus a few formulas: gear direction and speed, levers and mechanical advantage, pulleys, inclined planes, hydraulics, pressure and buoyancy, center of gravity and simple circuits. Aviation candidates will meet these ideas again: a helicopter's main rotor transmission is a gear train that turns fast engine speed into slower rotor speed.
The technique: name the principle, then compute
Before any arithmetic, name the rule the question is built on. Gears in mesh alternate direction. A lever balances when force times distance is equal on both sides. A pulley system's advantage equals the number of rope segments holding the load. Once the rule is named, the numbers usually take seconds.
Three worked examples
1. Gear train. Gear A (20 teeth) turns clockwise at 60 rpm and drives gear B (40 teeth), which drives gear C (10 teeth). Which way and how fast does C turn? Meshing gears alternate: A clockwise, B counterclockwise, C clockwise. Speed scales inversely with teeth: B turns 60 × 20/40 = 30 rpm, and C turns 30 × 40/10 = 120 rpm. Shortcut: a middle gear like B never changes the overall ratio, so C = 60 × 20/10.
2. Lever. A 6-foot bar rests on a pivot 2 feet from a 150-pound load. What downward push at the far end balances it? The load arm is 2 feet and the effort arm 4 feet. Balance: 150 × 2 = F × 4, so F = 75 pounds. The trap answer, 300, divides the wrong way: a longer effort arm means less force, not more.
3. Pulleys. A block and tackle has four rope segments holding up the moving block. Ignoring friction, what pull lifts a 200-pound load? 50 pounds, or 200 ÷ 4. The price: to raise the load 1 foot, you pull 4 feet of rope. Count only the segments that hold up the moving block.
Traps
- Direction in long gear chains. Count along: odd-numbered gears turn like the first, even-numbered ones the other way.
- Bigger gear, faster turn. It's the reverse: the gear with more teeth turns slower.
- Force vs distance. Mechanical advantage cuts the force and multiplies the distance; ignoring friction, work in equals work out.
- Belts. An open belt keeps the direction; a crossed belt reverses it.
- Random answers at the 15-minute mark. The FAQ advises against them on adaptive subtests.
Pacing
Fifteen minutes is short. Our timed set runs 20 questions in that time, 45 seconds each, which is a fair working pace: about 10 seconds to name the principle and 30 to apply it. A question that takes more than a minute deserves your best reasoned choice and a move on.
Practice it here
We don't imitate adaptivity: our MCT practice is fixed-length, with a timed set of 20 questions in 15 minutes. Each setup is described in words, and every explanation names the principle. Start in practice mode, then the timed set. The Navy's OAR has its own adaptive mechanical test; see OAR Mechanical Comprehension for fluids, gases and circuits.
How to solve a SIFT mechanical comprehension question
- Picture the setup and name the principle it tests: gears, lever, pulley, fluid or circuit.
- Write the one rule that applies, such as force times distance equal on both sides.
- Settle the direction first: which way it turns, which side goes up.
- Plug in the numbers; most questions need one multiplication or division.
- Sanity-check: a machine that lowers the force raises the distance; it can't lower both.
- Commit and move on; don't plan on going back.
FAQ
How many questions are on the SIFT Mechanical Comprehension Test?
It varies. The MCT is computer-adaptive with a 15-minute limit, so question counts differ between examinees (SIFT FAQ V2.0).
What topics are on SIFT mechanical comprehension?
Simple machines such as gears, levers, pulleys and inclined planes, plus fluids, pressure and basic electricity, at an introductory physics level.
Is there a guessing penalty on SIFT mechanical comprehension?
The rule differs from Simple Drawings: answering too few questions before time expires can bring a penalty, and random guessing at the end usually does more harm. Keep a steady pace.
Is your mechanical practice adaptive?
No. Our MCT practice is fixed-length, 20 questions in 15 minutes in timed mode. We don't imitate the adaptive engine.
Know where you stand in 15–20 minutes
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Take the free diagnosticUpdated 2026-10-04. Facts are checked against primary sources — see methodology.