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a ball bearing is a type of rolling-element bearing which uses balls to maintain the separation between the moving parts of the bearing.

Ball Bearing

a ball bearing is a type of rolling-element bearing which uses balls to maintain the separation between…

An illustration of boys carrying crates.

Boys Carrying Crates

An illustration of boys carrying crates.

"... a farmer with a crowbar, as shown, can move a rock which with his hands alone he could not stir." —Quackenbos 1859

Crowbar and Stone

"... a farmer with a crowbar, as shown, can move a rock which with his hands alone he could not stir."…

A vehicle that sustains itself in and propels itself through the air; an airplane, helicopter, glider, or the like.

Early Type Flying Machine

A vehicle that sustains itself in and propels itself through the air; an airplane, helicopter, glider,…

"[This illustration] represents a moveable pulley. A is the wheel. One end of the rope is fastened to a support at D, while the power is applied to the other at P." —Quackenbos 1859

Moveable Pulley

"[This illustration] represents a moveable pulley. A is the wheel. One end of the rope is fastened to…

A farm tool having one or more heavy blades to break the soil and cut a furrow prior to sowing

Motile Plow

A farm tool having one or more heavy blades to break the soil and cut a furrow prior to sowing

"A pulley is a grooved wheel, around which a rope is passed, and is either fixed or moveable." — Goodrich, 1844

Pulley

"A pulley is a grooved wheel, around which a rope is passed, and is either fixed or moveable." —…