# Gr

**Graceful Graph**- A graph is said to be graceful if you can number the n vertices with the integers from 1 to n and then label each edge with the difference between the numbers at the vertices, in such a way that each edge receives a different label.
**Grad Operator**- The del or grad operation means to take the derivative with respect to distance, in 3 dimensions.
**Grade**- Grade is used to define an angle, grade of sandpaper, amongst others..
**Grade of a Slope**- The pitch of a slope, and is often expressed as a percent tangent, or rise over run.
**Graded Index Fibre**- An optical fibre whose core refractive index decreases from its centre out to its edge.
**Gradient**- The rate of change of a quantity.
**Graduation Mark**- The marks that define the scale intervals on a measuring instrument are known as graduation marks.
**Graham′s Law**- The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
**Grain**- An individual crystal in a poly-crystalline metal or alloy.
**Grain Coarsening**- A heat treatment that produces excessively large austenitic grains.
**Grain Size**- For metals, a measure of the areas or volumes of grains in a polycrystalline material, usually expressed as an average when the individual sizes are fairly uniform.
**gram**- The CGS unit of mass equal to 10
^{-3}kg. **gramme**- Older spelling of gram, the CGS unit of mass equal to 10
^{-3}kg. **Grana**- Stacks of thylakoids in chloroplasts.
**Granularity**- The basic size of units that can be manipulated.
**Graph**- A pictorial presentation of the relation between two or more variables.
**Graph Completeness**- A graph is complete if any two of its vertices are connected by exactly one edge. A complete graph with N vertices is often denoted as KN.
**Graph Paper**- Paper that is printed with fine lines making up a regular grid.
**Graph Theory**- The mathematics of complicated networks.
**Graphene**- An allotrope of carbon, whose structure is one-atom-thick planar sheets of sp
^{2}-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. **Graphic Level Recorder**- A device for recording signal level in dB vs. time on a tape. The level in dB vs. angle can be recorded also for directivity patterns.
**Graphic Statics**- A method of analyzing a structure by visual diagrams rather than algebraic formulas.
**Graphical User Interface**- Abbreviated to GUI and pronounced "gooey". It is the programming code defining the operation and graphics displayed on a computer monitor.
**Graphics Card**- An expansion card which the PC uses to control the output graphics.
**Graphite**- An amorphous form of carbon, made of carbon atoms bound hexagonally in sheets.
**Gravimetric Energy Density**- Weight based energy density.
**Gravitational Collapse**- When a massive body collapses under its own weight.
**Gravitational Confinement**- The containment of nuclei under the influence of a gravitational field.
**Gravitational Constant**- G = 6.67x10
^{-11}Nm^{2}kg^{-2} **Gravitational Field**- The space surrounding an object where each location is assigned a value equal to the gravitational force experienced by one unit of mass placed at that location.
**Gravitational Interaction**- The interaction of particles due to their mass/energy.
**Gravitational Mass**- The property of a particle that determines the strength of its gravitational interaction with other particles.
**Gravitational Potential**- The worrk done in bringing a unit mass from infinity to that point. The assumption being that the gravitational potential is zero at infinity.
**Gravitational Potential Energy**- The work done by the force of gravity when an object falls from a particular point in space to the location assigned the value of zero.
**Gravitational Redshift**- The decrease in the frequency of electromagnetic waves due to a gravitational field.
**Gravitational Wave**- Ripple in the structure of space-time which may occur individually or as continuous radiation.
**Gravitationally Bound**- Objects held in orbit about each other by their gravitational attraction.
**Graviton**- The carrier particle of the gravitational interactions; not yet directly observed.
**Graviton Decoupling**- An epoch, early in the life of the universe, in which a density was reached such that gravitons no longer constantly interacted with other particles.
**Gravity**- One of the forces of nature. It is an attractive force exerted between two or more particles all of which have mass.
**Gravity Dam**- A dam constructed so that its great weight resists the force of water pressure.
**Gravity Separation**- Under the influence of gravity, separation of immiscible phases allows the denser phase to settle out.
**Gravity, Standard Acceleration due to**- g = 9.80665 ms
^{-2} **Gravity Wave**- A wave disturbance caused by the acceleration of masses.
**Gray**- This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material.
**Grease**- A lubricant composed of an oil or oils thickened with a soap, soaps or other thickener to a semisolid or solid consistency.
**Grease Gun**- A tool which is used for lubrication tasks.
**Great Circle**- A circle on the surface of a sphere whose centre is the centre of the sphere.
**Great Year**- Or Platonic Year, the period of one complete cycle of the equinoxes around the ecliptic, about 25800 years.
**Greater Than**- An inequality that says the variable on the left is greater than the variable to the right of the inequality.
**Greater than or Equal to**- An inequality that says the variable on the left is greater than or equal to the variable to the right of the inequality.
**Greatest Common Divisor**- The greatest common factor of two numbers is the largest number that divides into both numbers evenly, with no remainder.
**Greatest Common Factor**- The greatest common factor of two numbers is the largest number that divides into both numbers evenly, with no remainder. For example, the greatest common factor of 60 and 84 is 12.
**Greatest Lower Bound**- The greatest lower bound of a set of real numbers, is the largest real number that is smaller than each of the numbers in the set.
**Greek Alphabet**- The Greek alphabet from alpha to omega.
**Green Vitriol**- Hydrated Iron II Sulphate.
**Greencap Capacitor**- A type of polyester capacitor that the manufacturer dips in green paint to make it distinctive from all other capacitors.
**Greenhouse Effect**- The 'greenhouse effect' is caused by certain gases in the atmosphere trapping heat radiated from the Earth.
**Greenhouse Gases**- The three most powerful long lived greenhouse gases in the atmosphere are: Carbon Dioxide (CO
_{2}), Methane (CH_{4}) and Nitrous Oxide (N_{2}O). **Greenockite**- Mineral, main source of cadmium sulphide.
**Greenwich Mean Time**- Local mean time at the Greenwich meridian.
**Gregorian Calendar**- This calendar modifies the Julian calendar for greater precision.
**Gresley, Sir Nigel**- One of Britain′s most famous steam locomotive engineers, who rose to become Chief Mechanical Engineer of the London and North Eastern Railway - LNER.
**Grid**- A tesselation of congruent squares sometimes used to measure distance.
**Grid Based Energy Storage**- Energy storage system connected to the electricity grid that is designed to smooth supply and demand requirements.
**Grid Bias**- A constant fixed potential applied between the grid and the cathode of a vacuum tube to establish an operating point.
**Grid Current**- The current that flows in the grid-to-cathode circuit of a vacuum tube.
**Grid Gap Tuning**- A method of changing the centre frequency of a resonant cavity by physically changing the distance between the cavity grids.
**Grid Leak Bias**- A self-bias provided by a high resistance connected across the grid capacitor or between the grid and cathode.
**Grille**- A facing across a duct opening, often rectangular in shape, containing multiple parallel slots through which air may be delivered or withdrawn from a ventilated space.
**Grinder**- Mechanical device used to smooth metals.
**Grinding Ratio**- Measure of the grinding performance defined as the volume of metal removed divided by the volume of grinding wheel worn away in the operation.
**Grit Size**- Specified size of the abrasive particles in grinding wheels and other abrasive tools. Determines metal-removal capability and quality of finish.
**Grommets**- The design of grommets is critical to the acoustic performance of any partition such as engine bay bulkhead.
**Gross**- One hundred and forty four pieces of something.
**Gross Error**- Undetected mistakes that cause a measurement to be very much farther from the mean measurement than other measurements.
**Gross Vehicle Weight**- The maximum loaded weight, including the vehicle itself, passengers, and cargo, for which a vehicle is designed and as specified by the manufacturer.
**Ground**- To connect some point of an electrical circuit or some item of electrical equipment to earth or to the conducting medium used in lieu thereof.
**Ground Clearance**- Distance between underside of a vehicle and the ground.
**Ground Clearance Line**- A curved line in the vehicle side view representing a group of planes above which specific vehicle components are to be located.
**Ground Clutter**- Unwanted echoes, from surrounding land masses, that appear on a radar indicator.
**Ground Constants**- The characteristics of the earth which affect surface propagation and ground reflection of an electromagnetic wave.
**Ground Effect**- The aerodynamic modification of the airflow beneath a vehicle caused by its close proximity to the ground.
**Ground Loop**- An alternative path in which voltage can travel.
**Ground Plane**- The earth or negative rail of a circuit. A large or significant mass that presents the effect of earth (ground) to a signal.
**Ground Plane Antenna**- A type of antenna that uses a ground plane as a simulated ground to produce low-angle radiation.
**Ground Potential**- Zero potential with respect to the ground or earth.
**Ground Reflection Loss**- The loss of RF energy each time a radio wave is reflected from the surface of the earth.
**Ground Screen**- A series of conductors buried below the surface of the earth and arranged in a radial pattern. Used to reduce losses in the ground.
**Ground Source Heat Pump**- The heat is collected using a fluid that flows through pipes laid in the ground.
**Ground State**- The lowest energy state of a system allowed by quantum mechanics.
**Ground Waves**- Radio waves which travel near the surface of the earth.
**Grounded Base**- A transistor amplifier circuit comparable to the grounded-grid (signal ground) tube circuit.
**Grounded Collector**- A transistor circuit comparable to the cathode-follower tube circuit. (Also called emitter follower.)
**Grounding**- Establishing an electric connection to the Earth in order to neutralize an object.
**Group**- A vertical column in the periodic table.
**Group Delay**- The rate of change of phase shift with respect to frequency.
**Group Index**- The ratio of the vacuum velocity of light to the group velocity in the medium.
**Group Velocity**- A group may be made up of a number of different frequencies, wavelengths and velocities that are superposed. Such a group would disperse with time if the wave velocity of each component is different.
**Grown Junction**- A method of mixing P-type and N-type impurities into a single crystal while the crystal is being grown.
**Growth**- Functions may grow monotonously or in jumps. Complexity of a system may grow exponentially with the system size.