Mechanical Comprehension Study Guide for the ASVAB

Mechanical Motion

• Questions may include topics such as:
  • Systems of pulleys
  • Systems of gears
  • Rotating wheels and disks
  • Cam and cam followers
  • Cranks and pistons

Mechanical Advantage

• Definition: Amplification of a force via a machine.
• Output force can be larger than the input force.
• Calculation:
  • Using force of effort and weight/load force:
    • MA = Load force / Effort force
  • Using distances:
    • MA = Distance load travels / Distance effort travels

Simple Machines

• Amplify only one force.
• Examples: Gears, inclined planes, levers, pulleys, screws, wedges, wheels and axles.

Gears

• MA is the ratio of the number of teeth of the driven gear to the driving gear.

Inclined Plane

• Easier to move objects by distributing work over a longer distance.
• MA is the slope length over the vertical rise.

Lever

• Three classes:
  • Class 1: Fulcrum between load and effort (e.g., seesaw).
    • MA = Distance from fulcrum to effort / Distance from fulcrum to load
  • Class 2: Fulcrum at one end with load closer (e.g., wheelbarrow).
    • Calculated similarly to Class 1
  • Class 3: Fulcrum at one end with effort closer.
    • MA = Load force / Effort force

Pulley

• MA is the ratio of the effort distance to the load distance.
• Multiple ropes: MA = Number of ropes attached.

Screw

• MA is effort distance to load distance.

Wedge

• Example: Axe.
• MA = Length of wedge / Width or height of wedge.

Wheel and Axle

• MA = Effort distance (radius of handle) / Load distance (radius of blade).

Compound Machines

• Composed of multiple simple machines.
• MA is the product of MAs of individual machines.

Structural Support

• Involves the strength or weakness of frameworks/columns.
• Consider distribution of structure in relation to support type/quantity.
• E.g., weight distribution among people carrying a load.

Properties of Materials

• Heat Conduction: Ease of conducting heat. Metals are good conductors.
• Flexibility: Ability to bend without breaking.
• Malleability: Ability to be reshaped into a new form.

The Physics Connection

• Requires understanding of fundamental physics.
• Important concepts:
  • Force (F = ma)
  • Action/reaction
  • Equilibrium
  • Pressure
  • Types of force: friction, gravity, magnetism, etc.
  • Work and energy
• Some questions require calculation.

Tips For Success

• Force needed is never more than the object's weight (excluding friction).
• Choose answers with mechanical explanations.
• Mechanical changes have both positives and negatives.