ASVAB - Mechanical Knowledge

Pressure

Force (in pounds) / Area (in square inches)

Gravity

Physical property that draws objects toward the center of Earth. Generates a weight force when multiplied by an object’s mass.

Applied force

Force a person or another object applies to an object through contact

Tension

Transmitted through string, rope, etc when forces are acting on opposite ends

Friction

Resistance to the motion of two objects or surfaces that touch (opposite to object’s motion)

Recoil

Occurs when something regains its original form when an object exerting force on it is removed; it’s also referred to as a spring force

Law of universal gravitation

Every object in the universe attracts every other object in the universe

Centrifugal force

The apparent outward force on a mass when it is rotated (tangent to the circle)

Centripetal force

The force that keeps an object moving in a circular path (always points toward the center of the circle, perpendicular to the direction of motion of an object)

Which is less: rolling friction or sliding friction?

Rolling friction

Spring force (elastic recoil)

S_{f} = Spring Constant x Distance Displaced

Work

Work = Force x Distance

Power

P = W/t (measured in watts)

Mechanical Advantage

Mechanical Advantage = Resistance/Effort = Output Force / Input Force

Mechanical Advantage (Lever)

MA = (Effort Arm Length) / (Resistance Arm Length)

Mechanical Advantage (wheel and axle)

MA = (Wheel Radius) / (Axle Radius)

Mechanical Advantage (pulley)

MA = Number of rope segments supporting the load

Mechanical Advantage (plane)

MA = (Slope Length) / (Slope Height)

Mechanical Advantage (wedge)

MA = (Wedge Length) / (Wedge Thickness)

Mechanical Advantage (screw)

MA = (Circumference) / (Pitch of threads)

1st class lever

Fulcrum between effort and load (seesaw)

2nd class lever

Load between fulcrum and effort (wheelbarrow)

3rd class lever

Effort between fulcrum and load (shovel)

Load

Object or resistance you’re trying to move

Effort

Force you apply to move the load

Conservation of Work in Ideal Machines (gears, hydraulics, etc)

s_1t_1=s_2t_2