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(civil engineering) A narrow body of water between two piers.
(crystallography) The movement of one atomic plane over another in a crystal; it is one of the ways that plastic deformation occurs in a solid. Also known as glide.
(electricity) The difference between synchronous and operating speeds of an induction machine. Also known as slip speed. Method of interconnecting multiple wiring between switching units by which trunk number 1 becomes the first choice for the first switch, trunk number 2 first choice for the second switch, trunk number 3 first choice for the third switch, and so on.
(electronics) Distortion produced in the recorded facsimile image which is similar to that produced by skew but is caused by slippage in the mechanical drive system.
(fluid mechanics) The difference between the velocity of a solid surface and the mean velocity of a fluid at a point just outside the surface.
(geology) The actual relative displacement along a fault plane of two points which were formerly adjacent on either side of the fault. Also known as actual relative movement; total displacement.
(materials) A suspension of fine clay in water with a creamy consistency, used in the casting process and in decorating ceramic ware. Also known as slurry.
(naval architecture) To part from an anchor by releasing the shackles from the anchor chain. The reduction in the distance a propeller advances, per unit time, due to yielding of the fluid.

A numerical value used in describing the performance of electrical couplings and induction machines. In an electrical coupling, slip is defined simply as the difference between the speeds of the two rotating members. In an induction motor, slip is a measure of the difference between synchronous speed and shaft speed.

When the stator windings of an induction motor are connected to a suitable alternating voltage supply, they set up a rotating magnetic field within the motor. The speed of rotation of this field is called synchronous speed, and is given by Eq. (1) or
1.

2.
Eq. (2), where f is the line frequency and p is the number of magnetic poles of the field. The number of poles is determined by the design of the windings. In accord with Faraday's voltage law, a magnetic field can induce voltage in a coil only when the flux linking the coil varies with time. If the rotor were to turn at the same speed as the stator field, the flux linkage with the rotor would be constant. No voltages would be induced in the rotor windings, no rotor current would flow, and no torque would be developed. For motor action it is necessary that the rotor windings move backward relative to the magnetic field so that Faraday's law voltages may be induced in them. That is, there must be slip between the rotor and the field. See also Electromagnetic induction; Induction motor.

The amount of slip may be expressed as the difference between the field and rotor speeds in revolutions per minute or radians per second. However, the slip of an induction motor is most commonly defined as a decimal fraction of synchronous speed, as in Eq. (3) or Eq. (4).
3.

4.
Here n is the motor speed in revolutions per minute, ω is its speed in radians per second, and s is the slip, or more properly the per unit slip. Typical full-load values of slip for an induction motor range from 0.02 to 0.15, depending on rotor design. Slip is sometimes expressed in percent of synchronous speed, rather than per unit. If an induction machine is driven faster than synchronous speed, the slip becomes negative, and the machine acts as a generator, forcing energy back into the electrical supply line. See also Electric rotating machinery.

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