Pair of pulleys attached to usually parallel shafts and connected by an encircling flexible belt (band) that can serve to transmit and modify rotary motion from one shaft to the other. Most belt drives consist of flat leather, rubber, or fabric belts running on cylindrical pulleys or of belts with a V-shaped cross section running on grooved pulleys. Another type of belt, used on some internal-combustion engines for connecting the crankshaft and camshafts, is the toothed (or timing) belt, a flat belt with evenly spaced transverse teeth that fit in matching grooves on the periphery of the pulley.

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In psychology, an urgent need pressing for satisfaction, usually rooted in some physiological deficiency or imbalance (e.g., hunger and thirst) and impelling the organism to action. Psychologists distinguish between drives that are innate and directly related to basic physiological needs (e.g., food, air, and water) and drives that are learned (e.g., drug addiction). Among the other drives psychologists have identified are achievement, affection, affiliation, exploration, manipulation, maternity, pain avoidance, sex, and sleep.

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