Pi

pi
A letter of the Greek alphabet. The lowercase is used to denote the number of times the diameter of a circle can be divided into the circumference.
Pi Bonds
A type of covalent bond in which the electron density is concentrated around the line bonding the atoms.
Piano Hinge
Designed to extend for the length of the moving part to which it is applied.
Piano Wire
High quality steel wire used for making springs.

PiB
Abbreviation of pebibyte, equal to two to the power of fifty bytes.
Pica
An old print size that is approximately the same as 12 point.
Picaxe
The name of a UK-sourced microcontroller system based on a range of Microchip PICs.
Pick Hammer
A hammer with a round head for conventional planishing and a small pick-shaped head for working away in sharp or tight corners.
Picket Fence Effect
The true spectrum of the signal being analyzed may have peaks at frequencies between the lines of the FFT spectrum, and the peaks in the FFT spectrum will not be at exactly the correct frequencies.
Pickling
The chemical removal of surface oxides and other contaminants from a material by immersion in an aqueous acid solution.
pico
Prefix representing a multiplication of 10-12
picogram
A mass equal to 10-12g.
picolitre
A volume equal to 10-12l.
picometre
A distance equal to 10-12 metres.
picosecond
A period of time equal to 10-12 seconds.
Picture
Visual representation of something.
Pie Chart
A strong representation of data with the size of the slice representing the fraction of the total.
Piecewise Function
A function is piecewise-defined, if its rule is given by more than one other formula for different sets of input.
Pier
A large pillar used to support a roof.
Piezo Sounder
Small crystal element that can emit very high sound levels while requiring low current.
Piezoelectric
Any material which provides a conversion between mechanical and electrical energy.
Pig Iron
The intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux.

Pile
A long, round pole of wood, concrete, or steel driven into the soil by pile drivers.
Pile Driver
A machine that repeatedly drops a heavy weight on top of a pile until the pile reaches solid soil or rock or cannot be pushed down any farther.
Pillow Lava
Interconnected, sack-like bodies of lava formed underwater.
Pilot Balloon
A balloon that ascends through the atmosphere at a constant rate and is tracked by a theodolite in order to obtain timed data for the computation of the wind speed and wind direction at various levels in the upper air above the station.
Pilot Bit
A router bit with a bearing at the end of the cutter that rides against the edge the material or a template to guide the cut.
Pilot Hole
A starting hole for large drills to serve as a guide.
Pin Connection
In two dimensions, a pin connection restrains two translation degrees of freedom but does not restrain rotation.
PIN Diode
A diode with a wide, lightly doped near intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region.
Pin Spanner
A spanner with pins on forked ends, used to turn an adjustable cup on the bottom bracket of a bicycle.
Pinchbeck
A cheap bronze alloy.
Pine
Easily worked and used where moderate strength and durability are required. Turpentine is obtained from the pine.
Pinhole
A small, sharp-edge hole without a lens which can function as an aperture or eye lens.
Pinion
The smaller of two mating or meshing gears. Can be either the driving or the driven gear.
Pink Noise
A random-like signal in which power is proportional to the inverse of frequency.
Pinna
The exterior part of the ear.
Pint
A derived British unit of volume.
Pion
The least massive meson.
Pipe
A hollow cylinder following certain dimension rules.
Pipe Cutter
A hand tool for cutting metal pipes.
Piston
A cylindrical part which reciprocates in the cylinder bore of an engine and transmits the force of the gas pressure through the connecting rod to the crankshaft.
Piston Crown
The very top of the piston.
Piston Driven Wind Tunnel
A type of shock tunnel in which energy is created by a piston being fired or driven down a cylinder.
Piston Pin
A pin that rests in two bored holes in the piston and passes through the eye of the connecting rod, to join the two together flexibly.
Piston Ring
An open-ended ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.
Piston Skirt
The cylindrical part of the piston which sits within the bore.
Pit Saw
The main tool of the trade of the pre industrial age saw.
Pitch
Pitch is the distance between the teeth on a gear.
Pitch - Vehicle Dynamics
The motion of a vehicle in which the front moves up and down relative to the static position.
Pitch Angle
The angle, as seen from the side, between the longitudinal body axis of an aircraft or similar body and a chosen reference line or plane, usually the horizontal plane.
Pitch Circle
The effective working circle of a gear which would be obtained if a pair of gears were replacedwith disks that transmitted the same motion in the same package space through contact friction.
Pitch Pine
A softwood with a colour similar to Scots pine but with strong marked figure. This wood has a lot of resin.

Pitch Sensitivity
The magnitude of aerodynamic downforce can markedly alter with changes to front ground clearance as a result of pitch movements. This can affect the vehicle performance and feel of the vehicle.
Pitchblende
The most important Uranium ore.
Pitched Howe Truss
Structural framework for supporting loads over long spans.
Pitched Pratt Truss
Structural framework for supporting loads over long spans.
Pitot, Henri
French astronomer, engineer and mathematician who invented the Pitot Tube in 1732.
Pitot Tube
An open ended tube arrangement to face against the current of a stream of fluid used in measuring the velocity head of a flowing medium.
Pitting
Localized corrosion of a metal surface, confined to a point or small area, that takes the form of cavities.
Pivot Point
The point around which something turns.
Pixel
Single picture element of a detection device.