ASVAB Review: Gears, Work, Friction, and Power

Vocabulary and concepts regarding mechanical gears, work calculations, types of friction, and power units based on ASVAB review materials.

Spur gears

Wheels with mating teeth cut in their surfaces so that one can turn the other without slippage.

Straight spur gears

Gears in which the mating teeth are cut so that they are parallel to the axis of rotation.

Pinion

The smaller of two gears of unequal size that are meshed together.

Helical spur gear

Also known as spiral gears, these have teeth cut slantwise across the working face so that each tooth has a leading end and a trailing end.

Thrust bearing

A special component placed at the end of a shaft to counteract the axial thrust generated by helical spur gears.

Internal gear

A gear with teeth on the inside of a ring pointing inward toward the axis of rotation, usually meshed with an external gear.

Sector gear

A portion of a gear used to save space and material when the motion of the pinion is limited.

Rack and pinion

A gear arrangement useful in changing rotary motion into linear motion.

Bevel gear

A type of gear used to connect shafts lying at an angle rather than parallel shafts.

Miter gear

A special case of bevel gear used to connect shafts at a $90$-degree angle, with gear faces beveled at $45$-degree angles.

Straight bevel gears

Bevel gears where the whole width of each tooth comes in contact with the mating tooth at the same time.

Spiral bevel gears

Gears with teeth cut to have advanced and trailing ends, providing smoother and quieter operation through progressive contact.

Worm and worm wheel

A gear combination where a threaded worm turns a wheel; a single-thread worm turns the wheel one tooth for each revolution.

Theoretical Mechanical Advantage (Gears)

Found by the formula $\text{M.A. (theoretical)} = \frac{T_o}{T_a}$, where $T_o$ is the number of teeth on the driven gear and $T_a$ is the number of teeth on the driver gear.

Work

Mechanical action performed when a resistance is overcome by a force acting through a measurable distance.

Foot-pound

The common unit of work, representing one pound of force applied through a distance of one foot.

Work Formula

$\text{WORK} = \text{FORCE} \times \text{DISTANCE}$.

Friction

The resistance that one surface offers to its movement over another surface, depending on the nature of the surfaces and the forces holding them together.

Rolling friction

A type of friction that is always less than sliding friction, utilized by ball and roller bearings.

Power

The rate of doing work, expressed as $\text{Power} = \frac{\text{Work}}{\text{Time}}$.

Horsepower (hp)

A standard unit of power equivalent to $33,000 \text{ foot-pounds}$ of work done in one minute.