ASVAB Subject Review: Friction, Power, Force, and Pressure

Vocabulary flashcards covering the concepts of friction, power units, mechanical force, pressure measurement, and basic machine elements like bearings and springs.

Friction

The resistance that one surface offers to its movement over another surface.

Rolling friction

A type of resistance that is always less than sliding friction.

Lubricants

Substances such as oil, grease, or soap used to decrease friction and cut down on wear.

Power

The rate of doing work, which always includes a time element.

Horsepower (hp)

The standard unit of power, defined as $33,000\,ft-lb$ of work done in one minute, or $550\,ft-lb/s$.

James Watt

The inventor of the steam engine who established the horsepower unit by experimenting with the work capacity of an average horse.

Force

A push or a pull exerted on, or by, an object.

Weight

A common term describing how much force or pull gravity is exerting on an object.

Pressure

Force per unit area, calculated using the formula $P = \frac{F}{A}$.

psi

The unit of measurement for pressure, standing for pounds per square inch.

Bourdon gage

A pressure-measuring device using a thin-walled metal tube bent into a C shape that tends to straighten when internal pressure increases.

Schrader gage

A sturdy gage recommended for fluctuating loads where a piston moves up a cylinder against the resistance of a spring.

Diaphragm-type gage

An instrument used for accurate measurements of comparatively slight pressures or small pressure differences.

Normal atmospheric pressure

The air pressure at sea level, which is approximately $14.7\,psi$ (rounded to $15\,psi$ in general contexts).

Aneroid barometer

A weather instrument containing a thin-walled metal box with a partial vacuum that measures atmospheric pressure changes.

Bearing

A support and guide that carries moving machine parts, maintaining their relationship to stationary parts while reducing friction.

Journal bearings

Sliding-type bearings used to guide and support revolving shafts, typically fitted with a liner of babbitt metal.

Thrust bearings

Bearings installed to resist axial thrust or force and limit axial movement on rotating shafts.

Springs

Elastic bodies that can be twisted, pulled, or stretched by force and return to their original shape when the force is released.

Equilibrator springs

Specific springs used to counterbalance a weight or thrust, such as gravitational or hydraulic forces.

Spiral springs

Also called clock or power springs, these are wound to store energy and gradually release it as they unwind.

Helical springs

The most common type of spring, which can be categorized into compression, extension (tension), or torsion types.