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jack, mechanical device

jack, mechanical device used to multiply a relatively small applied force so that it can lift and support heavy loads, or sometimes, move massive objects into a desired position. The lever jack, often used in lifting automobiles, has a lever combined with a ratchet; the lever is used to lift the load a small distance and the ratchet prevents the load from falling back while the lever is reset so that the process can be repeated. In the screw jack the load is moved or lifted by the turning of a screw; the pitch of the screw threads is arranged so that friction is sufficient to hold the load in place when the torque applied to the screw is released. In yet another form of jack a hydraulic device is used. See hydraulic machine.

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jack, in zoology

jack: see pompano; tuna.

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jack

In practical mechanics, portable hand-operated device for raising heavy weights through short distances, exerting great pressures, or holding assembled work firmly in position. The ratio of the load to the amount of force applied to the handle can be made quite high by using a gear or screw to regulate the upward extension. A ratchet allows a heavy weight to be raised in short successive stages. Though limited by the requirements of portability and ease of manual operation, jacks may lift, or exert a force of, several tons. A familiar example is the automobile jack, used to raise one end of a car to change a tire.

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jack

Any of more than 150 species of fishes (family Carangidae, order Perciformes) found in temperate and tropical portions of the Atlantic, Pacific, and Indian oceans and occasionally in fresh or brackish water. Though body size and shape vary greatly, many species have small scales that create a smooth appearance, a laterally compressed body, rows of large spiky scales along the side near the tail fin, and a deeply forked tail. Many have a bluish green, silvery, or yellowish sheen. Jacks are important commercially and are favoured sport fishes. See also amberjack.

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jack

A socket, receptacle or port. The term is widely used in the telephony and audio/video worlds; for example, the Registered Jack-11 (RJ-11) is the common telephone wall outlet. Microphones plug into phono jacks on amplifiers. In networking, "port" is the preferred term as in "the switch has 24 RJ-45 ports." However, people coming from the telephony world might say "the switch has 24 RJ-45 jacks." See audio jack, RJ-11, RJ-45 and plugs & sockets.

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jack¹

1. a sailor

2. the male of certain animals, esp of the ass or donkey

3. a mechanical or hydraulic device for exerting a large force, esp to raise a heavy weight such as a motor vehicle

4. one of four playing cards in a pack, one for each suit, bearing the picture of a young prince; knave

5. Bowls a small usually white bowl at which the players aim with their own bowls

6. Electrical engineering a female socket with two or more terminals designed to receive a male plug (jack plug) that either makes or breaks the circuit or circuits

7. a flag, esp a small flag flown at the bow of a ship indicating the ship's nationality

8. Nautical either of a pair of crosstrees at the head of a topgallant mast used as standoffs for the royal shrouds

9. a part of the action of a harpsichord, consisting of a fork-shaped device on the end of a pivoted lever on which a plectrum is mounted

10. any of various tropical and subtropical carangid fishes, esp those of the genus Caranx, such as C. hippos (crevalle jack)

11. one of the pieces used in the game of jacks

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jack²

Archaic a drinking vessel, often of leather

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jack [jak]

(electricity)

A connecting device into which a plug can be inserted to make circuit connections; may also have contacts that open or close to perform switching functions when the plug is inserted or removed.

(mechanical engineering)

A portable device for lifting heavy loads through a short distance, operated by a lever, a screw, or a hydraulic press.

(mineralogy)

sphalerite

(textiles)

A frame in lace-manufacturing equipment that has horizontal bars to support fixed vertical wires, against which bobbins containing the yarn can freely revolve.

An oscillating lever that raises the harness of a dobby loom.