jack


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jack:

see pompanopompano
, common name for fishes of the genus Trachinotus, members of a large and important family (Carangidae) of mackerellike fishes, abundant in warm seas around the world.
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; tunatuna
or tunny,
game and food fishes, the largest members of the family Scombridae (mackerel family) and closely related to the albacore and bonito. They have streamlined bodies with two fins, and five or more finlets on the back.
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.

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 machinehydraulic machine,
machine that derives its power from the motion or pressure of water or some other liquid. Hydraulic Engines

Water falling from one level to a lower one is used to drive machines like the water wheel and the turbine.
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.

Jack

 

a naval flag that is raised daily on the bow of first-class and second-class ships only when they are at anchor. It is flown with the ensign (usually from 8 A.M. until sunset). The jack of warships of the Soviet Union is a red flag on which is depicted a five-pointed star in white outline with the hammer and sickle in the center.


Jack

 

a mechanism for lifting heavy piece loads during repair, assembly, or loading and unloading operations. Jacks are characterized by small dimensions and light weight (usually not more than 1 percent of the lifting capacity), low speed (0.01-0.25 m/min), and a lifting height of 0.15-1.0 m. However, special-purpose jacks may have a lifting capacity of several hundred tons and may lift loads to a height of several meters. A jack can raise loads smoothly, stop them accurately, and hold them at a given height. They are classified according to the type of drive as manual and electric and according to the principle of operation and their design features as rack-and-pinion, screw, and hydraulic.

The main part of a rack-and-pinion jack is the load-carrying rack, with a load-supporting pan for the load and with the lower end (foot) bent at a right angle in order to lift loads with a low-slung bearing surface. According to the type of transmission mechanism, rack-and-pinion jacks are divided into rack-and-lever and gear types. In rack-and-lever jacks the rack is advanced by a rocking drive lever; in the gear types it is advanced by means of a pinion rotated by a drive crank. Jacks with a load capacity of up to 6 tons have a one-step transmission, those with a capacity of 6-15 tons have a two-step transmission, and those with a capacity of more than 15 tons have a three-step transmission. Loads that have been lifted by the jack are held up by locking devices. The efficiency of a rack-and-pinion jack with a single-gear drive is 0.85; with a double-gear drive, it is 0.7.

The main part of a screw jack is a screw with a swiveling load-supporting pan; the screw is rotated by a crank. Jacks having sliding carriages that are also equipped with a screw are used to move loads horizontally. The load is held in position by the self-braking action of the screw, thus ensuring a high degree of operating safety. The load capacity of screw jacks usually does not exceed 20 tons, but special jacks are made with capacities of 100 tons and higher and with lifts of up to 2 m. The efficiency of screw jacks does not exceed 0.3-0.4.

Hydraulic jacks may have either periodic action with manual drive or continuous action with mechanical drive. In the periodic-action type, a plunger that supports the load is raised by a working fluid, which is forced into the lower cavity of the housing by a piston pump operated by a hand lever and equipped with intake and delivery valves. The load is lowered by letting the working fluid pass from the housing into the pump reservoir. In the continuous-action type the working fluid is forced into the space above the piston, so that it is not the piston but the housing—together with the load, reservoir, and pump—that is raised. The housing and piston are interconnected with return springs. If the cylinder is supported from below in its extreme upper position and the bypass valve is opened, the piston will rise under the action of the spring forces, and the fluid will flow into the reservoir. Supports are then put under the piston again, and the operating cycle is repeated without shifting the jack. Hydraulic jacks combine the advantages of the screw and rack-and-pinion types. They have high efficiency (0.75-0.80), smooth motion, accurate stopping, automatic braking, compactness, and large load capacity (up to several hundred tons). Their drawbacks are low speed and small lift height per operating cycle.

REFERENCES

Kifer, L. G., and I. I. Abramovich. Gruzopod”emnye mashiny, 2nd ed., part 1. Moscow, 1956.
Mashinostroenie: Entsiklopedicheskii spravochnik, vol. 9. Moscow, 1949. Pages 857-63.

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)
(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.

jack

jack, 2
1. A portable machine, variously constructed for exerting great force for moving a heavy body through a short distance. Also see hydraulic jack; jackscrew.
2. An electrical receptacle into which a plug, 7 is inserted to make electrical contact between communication circuits.

jack

jackclick for a larger image
A device to lift aircraft off the ground. Jacks are used for undercarriage retraction, wheel change, rigging checks, etc.

jack

1
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

jack

2
Archaic a drinking vessel, often of leather

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 and sockets.
References in classic literature ?
This evening he was particularly careful not to neglect his duty, for he had just come from a conference with the boy's father and mother in which it had been impressed upon him that he must exercise the greatest care to prevent Jack visiting the music hall where Ajax was being shown.
Kneeling upon him, Jack tore strips from a sheet and bound the man's hands behind his back.
Long Jack, a basket at his feet and mittens on his hands, faced Uncle Salters at the table, and Harvey stared at the pitchfork and the tub.
But Jack Pumpkinhead grew a lot of things in his garden besides pumpkins, so he cooked for them a fine vegetable soup and gave Dorothy, Ojo and Toto, the only ones who found it necessary to eat, a pumpkin pie and some green cheese.
Mebbe this is a case where a hunch after the draw is better'n the hunch before," Kearns remarked; "wherefore duty says, 'Lift her, Jack, lift her,' and so I lift her another five thousand.
Each day he spent from an hour to two hours in the cage, watching the rehearsing, with nothing for him and Jack to do save stand vigilantly on guard.
Each time Ozma has carved me a new head just like the old one, and as my body is by far the largest part of me, I am still Jack Pumpkinhead, no matter how often I change my upper end.
Steady there; don't be such an ass, Jack," says the captain; "we haven't got the best wicket yet.
Because if it was, I'd take the lead with you, Jack, and be as wise as Begone, dull Care
He's in the hospital now,' said Jack Hopkins, 'and he makes such a devil of a noise when he walks about, that they're obliged to muffle him in a watchman's coat, for fear he should wake the patients.
You're not Bodymaster for life, Jack McGinty, and by God
Jacks said, "I have not come here to gratify any personal curiosity.