Comprehensive preparation for the Armed Services Vocational Aptitude Battery
Understanding mechanical principles, physical forces, and devices
The Mechanical Comprehension (MC) section of the ASVAB tests your understanding of basic mechanical principles, physical forces, and how mechanical devices work.
Test Format: On the CAT-ASVAB (computerized version), you'll have 16 questions in 20 minutes. On the P&P-ASVAB (paper version), you'll have 25 questions in 19 minutes. While this section doesn't contribute to your AFQT score, it is important for qualifying for technical military occupational specialties.
| Machine Type | Description | Mechanical Advantage | Examples |
|---|---|---|---|
| Lever | Rigid bar pivoting around a fixed point | Effort arm ÷ Load arm | Crowbar, seesaw, scissors |
| Pulley | Wheel with grooved rim for rope/cable | Number of supporting rope segments | Flag pole, block and tackle |
| Inclined Plane | Sloped surface to raise objects | Length ÷ Height | Ramps, wedges, screws |
| Wheel and Axle | Wheel attached to central axle | Radius of wheel ÷ Radius of axle | Doorknob, steering wheel |
| Concept | Formula | Unit |
|---|---|---|
| Work | W = F × d | Joule (J) |
| Power | P = W ÷ t | Watt (W) |
| Kinetic Energy | KE = ½mv² | Joule (J) |
| Torque | T = F × d | Newton-meter (N·m) |
| Concept | Formula | Application |
|---|---|---|
| Pressure | P = F/A | Hydraulic systems, tire pressure |
| Hydrostatic Pressure | P = ρgh | Dams, diving, tanks |
| Buoyancy | Fbuoyant = ρgV | Ships, submarines, balloons |
| Flow Rate | Q = A × v | Pipe sizing, pump selection |
| Property | Description | Examples |
|---|---|---|
| Tensile Strength | Resistance to pulling forces | Cables, chains |
| Compressive Strength | Resistance to pushing forces | Columns, foundations |
| Shear Strength | Resistance to sliding forces | Bolts, rivets |
| Elasticity | Ability to return to original shape | Springs, rubber |
Problem: A first-class lever has its fulcrum 2 feet from the load and 6 feet from the effort. How much force is needed to lift a 300-pound load?
Solution:
Answer: 100 pounds of force required
Problem: A pulley system has 4 supporting rope segments. How much force is needed to lift a 200-pound crate?
Solution:
Answer: 50 pounds of force required
Problem: A 1,500-pound car accelerates from 0 to 60 mph in 8 seconds. What is the average force applied?
Solution:
Answer: Approximately 512 pounds
Problem: A block of wood (volume 0.1m³, mass 80kg). Will it float in water (density 1,000kg/m³)?
Solution:
Answer: Yes, it will float
Problem: A 20-tooth gear drives a 60-tooth gear. Driver rotates at 120 RPM. What is the driven gear's speed?
Solution:
Answer: 40 RPM
Pitfall: "Simple machines create energy"
Reality: They only transform or redirect forces
Pitfall: Confusing mass and weight
Correction: Mass is resistance to acceleration; weight is force of gravity
Pitfall: Confusing pressure and force
Correction: Pressure = Force ÷ Area
First Class: Fulcrum between Load and Effort
Second Class: Load between Fulcrum and Effort
Third Class: Effort between Fulcrum and Load
Inertia (1st Law)
Second Law (F=ma)
Reaction (3rd Law)
Down: Pressure increases with depth
All directions: Pressure acts equally
Density matters: Higher density = more pressure
This practice test contains 30 multiple-choice questions. Try to answer all within 20 minutes to simulate the ASVAB test conditions.
A first-class lever has its fulcrum 2 feet from the load and 8 feet from the effort. What is the mechanical advantage?
Answer: C) 4
MA = Effort arm ÷ Load arm = 8ft ÷ 2ft = 4
In a pulley system, mechanical advantage equals:
Answer: B) Number of supporting rope segments
The load is distributed among supporting rope segments.
A ramp is 12 feet long and rises 3 feet. What is its mechanical advantage?
Answer: B) 4
MA = Length ÷ Height = 12ft ÷ 3ft = 4
A gear with 15 teeth drives a gear with 45 teeth. Driver rotates at 120 RPM. What is driven speed?
Answer: A) 40 RPM
Speed ratio = Teeth on driver ÷ Teeth on driven = 15 ÷ 45 = 1/3
Driven speed = 120 RPM × 1/3 = 40 RPM
Which is a second-class lever?
Answer: B) Wheelbarrow
Second-class lever has load between fulcrum and effort.
Review the explanations for each question to understand the correct answers.