Pe

Peak

Extreme value of a varying quantity, measured from the zero or mean value.

Peak Hold

The peak signal level for each frequency component is held for display.

Peak Pick

A parameter estimation technique where the peak value of the imaginary part of the frequency response function is used to estimate the mode shape value at that point.

Peak to Peak Value

The over-all amplitude of a signal measured from its lowest peak to its most highest peak.

Peak Value

The instantaneous maximum value of a waveform.

Pearl Ash

An old fashioned name for Potassium Carbonate.

Pearlite

A lamellar aggregate of ferrite and cementite.

Pearson Product Moment Correlation Coefficient

A dimensionless index that reflects the extent of a linear relationship between two data sets.

Peat

Partially carbonized vegetable material, usually found in bogs.

pebibyte

Equal to two to the power of fifty bytes.

Peck

An old unit of volume.

Pediment

In a classical-style building, the triangular segment between the horizontal entablature and the sloping roof.

Peen Hammer

A body hammer with a pein of triangular section with a fairly sharply shaped end.

Peening

The mechanical working of metals by means of hammer blows.

Peierls Stress

The stress required to move a dislocation.

Pein Hammer

A body hammer with a pein of triangular section with a fairly sharply shaped end.

Peltier Effect

The change in temperature produced at a junction between two dissimilar metals or semiconductors when an electric current passes through the junction.

Pendentive

A curved support shaped like an inverted triangle, used to support a dome.

Pendulums

There are a number of different forms of pendulum. The main characteristic being that when the mass is displaced from it's position of rest it will oscillate at a fixed frequency.

penetrant inspection

A method of nondestructive testing for determining the existence and extent of discontinuities that are open to the surface in the part being inspected.

Pennyweight

An old unit of mass equal to 24 grains.

Pentad

A period of 5 days.

Pentadecagon

A 15 sided polygon.

Pentagon

A polygon with five sides.

Pentane

C₅H₁₂

The fifth member of the paraffin series. Pentane exists in three isomeric forms.

Pentanol

C₅H₁₁OH

A colourless liquid at room temperature with a choking aroma.

penumbra

The transition region between the darkest shadow and full brightness.

Peptide

A short polymer made by linking together amino acid molecules.

Per Diem

A traditional unit of frequency equal to once a day.

Per Mensem

A traditional unit of frequency equal to once a month.

Perceived Colour

Also known as visual colour is the quality of light emission as conveyed by the human eye, combining the impressions of 3 types of light-sensitive cells which the eye contains.

Perfect Cube

An integer is a perfect cube if it is of the form m³ where m is an integer.

Perfect Number

A positive integer that is equal to the sum of its proper divisors.

Perfect Power

An integer is a perfect power if it is of the form mⁿ where m and n are integers and n>1.

Perfect Square

An integer is a perfect square if it is of the form m² where m is an integer.

Perfluoromethane

Alternative name for Tetrafluoromethane.

Periapsis

The point of an orbit nearest to the center of attraction of an orbiting body.

Pericentre

The point on a spacecrafts orbit at which it is nearest to the centre of mass of the system.

Perigee

The point of a satellite's orbit closest to Earth.

Perihelic Opposition

When the Earth passes between a planet and the Sun when the planet is at its closest from the Sun.

Perihelion

The point of closest approach for any object orbiting the sun.

Period

The time taken for a full cycle of motion in a system executing harmonic motion.

Periodic

A term used to refer to a pattern of motion which repeats exactly after a given interval or period.

Periodic Law

The properties of the elements are periodic functions of their atomic numbers.

Periodic Table

The most commonly used arrangement of the periodic system.

Peritectic

An isothermal reversible reaction in metals where a liquid phase reacts with a solid phase to produce a single, different, solid phase upon cooling.

Perl

An interpreted language optimised for scanning arbitrary text files.

Permangante of Potash

Old fashioned name for Potassium Manganate VII.

Permeability

1. passage or diffusion of a gas, vapor, liquid, or solid through a material without physically or chemically affecting it.
2. Term used to express various relationships between magnetic induction and magnetizing force; either absolute permeability or specific (relative) permeability.

Permeability of Free Space

μ₀ = 4πx10^-7 Hm^-1

Permeance

The property which determines the magnitude of magnetic flux in a material.

Permittivity

The proportionality constant between the dielectric displacement D and the electric field E.

Permittivity of Free Space

ε₀ = 8.85419x10^-12 Fm^-1

Permutations and Combinations

A permutation is a particular sequence of a given set of objects. A combination is the set itself without reference to order.

Perpendicular

At right angles to. A line at right angles to another line or to a plane.

Perspex

Tradename for Polymethyl Methacrylate Resin.

Pesticide

A chemical or biological agent that kills pests.

Peta

Prefix representing a multiplication of 10¹⁵

Petrol

A volatile, flammable liquid mixture of hydrocarbons, obtained from petroleum and used as a fuel for internal-combustion engines.

Petrol Engine

An internal-combustion engine in which the fuel is petrol that is drawn or injected into the cylinder along with air and ignited with an electric spark.

Petroleum

An oily, thick, flammable, usually dark coloured liquid that is a form of bitumen or a mixture of various hydrocarbons, occurring naturally in various parts of the world and often separated by distillation into petrol, naphtha, benzene, kerosene and paraffin.

Pewter

Tin-base white metal containing antimony and copper: 1 to 8% Sb and 0.25 to 3% Cu.