Balance of tradeThe balance of trade, commercial balance, or net exports (sometimes symbolized as NX), is the difference between the monetary value of a nation's exports and imports over a certain time period. Sometimes a distinction is made between a balance of trade for goods versus one for services. The balance of trade measures a flow of exports and imports over a given period of time. The notion of the balance of trade does not mean that exports and imports are "in balance" with each other.
Displacement currentIn electromagnetism, displacement current density is the quantity ∂D/∂t appearing in Maxwell's equations that is defined in terms of the rate of change of D, the electric displacement field. Displacement current density has the same units as electric current density, and it is a source of the magnetic field just as actual current is. However it is not an electric current of moving charges, but a time-varying electric field. In physical materials (as opposed to vacuum), there is also a contribution from the slight motion of charges bound in atoms, called dielectric polarization.
Conjugate diametersIn geometry, two diameters of a conic section are said to be conjugate if each chord parallel to one diameter is bisected by the other diameter. For example, two diameters of a circle are conjugate if and only if they are perpendicular. For an ellipse, two diameters are conjugate if and only if the tangent line to the ellipse at an endpoint of one diameter is parallel to the other diameter. Each pair of conjugate diameters of an ellipse has a corresponding tangent parallelogram, sometimes called a bounding parallelogram (skewed compared to a bounding rectangle).
Balance of paymentsIn international economics, the balance of payments (also known as balance of international payments and abbreviated BOP or BoP) of a country is the difference between all money flowing into the country in a particular period of time (e.g., a quarter or a year) and the outflow of money to the rest of the world. These financial transactions are made by individuals, firms and government bodies to compare receipts and payments arising out of trade of goods and services.
AreaArea is the measure of a region's size on a surface. The area of a plane region or plane area refers to the area of a shape or planar lamina, while surface area refers to the area of an open surface or the boundary of a three-dimensional object. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat.
Relative permittivityThe relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field. Permittivity is a material's property that affects the Coulomb force between two point charges in the material. Relative permittivity is the factor by which the electric field between the charges is decreased relative to vacuum.
Static electricityStatic electricity is an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is named in contrast with current electricity, where the electric charge flows through an electrical conductor or space, and transmits energy. A static electric charge can be created whenever two surfaces contact and or slide against each other and then separated.
Static clingStatic cling is the tendency for light objects to stick (cling) to other objects owing to static electricity. It is common in clothing, but occurs with other items, such as the tendency of dust to be attracted to, and stick to, plastic items. In clothing, static cling occurs from static electricity. An electrostatic charge builds up on clothes due to the triboelectric effect when pieces of fabric rub against each other, as happens particularly in a clothes dryer. The separate positive and negatively charged surfaces attract each other.
Triboelectric effectThe triboelectric effect (also known as triboelectricity, triboelectric charging, triboelectrification, or tribocharging) describes electric charge transfer between two objects when they contact or slide against each other. It can occur with different materials, such as the sole of a shoe on a carpet, or between two pieces of the same material. It occurs with differing amounts of charge transfer (tribocharge) for all solid materials and all contacts and sliding.
Antistatic deviceAn antistatic device is any device that reduces, dampens, or otherwise inhibits electrostatic discharge, or ESD, which is the buildup or discharge of static electricity. ESD can damage electrical components such as computer hard drives, and even ignite flammable liquids and gases. Many methods exist for neutralizing static electricity, varying in use and effectiveness depending on the application. Antistatic agents are chemical compounds that can be added to an object, or the packaging of an object, to help deter the buildup or discharge of static electricity.
Deformation (physics)In physics and continuum mechanics, deformation is the transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body. A deformation can occur because of external loads, intrinsic activity (e.g. muscle contraction), body forces (such as gravity or electromagnetic forces), or changes in temperature, moisture content, or chemical reactions, etc. Strain is related to deformation in terms of relative displacement of particles in the body that excludes rigid-body motions.
