The acoustic impedance of a material is defined as the product of its density and velocity of acoustic waves.
A map projection is a systematic transformation of the latitudes and longitudes of locations from the surface of a sphere or an ellipsoid into locations on a plane
During the data projection process, distortions of at least one of the geographical features are introduced: shape, area, direction, distance. Compared to their prevailing properties, the projections are distinguished in equidistant, equivalent and conform, depending on whether they maintain distances, areas or angles.
When interposing a material between charged bodies, the electrical force changes considerably. The electric force is maximum in the vacuum and therefore any other material, called dielectric, has the property of attenuating the force between the electric charges.
The relative dielectric constant (εr) is defined as the ratio between the electrical force in the vacuum and the electrical force in a substance.
The velocity of electromagnetic waves in the vacuum is equal to c = 3 * 108 m/s while in a homogeneous and isotropic medium it is calculated by the following formula:
v = c /
The elastic waves propagate only in the presence of matter; the perturbation consists of a displacement of the particles that constitute the material and the propagation is due to the characteristics of stiffness and elasticity of the medium.
Flow of electric charges, resulting in the application of an electric potential difference to a conducting body. The electric charges in motion can be of different nature. In liquids and gases, the electric current is constituted by positive charges and by negative charges (positive ions and negative ions), while in the metallic conductors the current is due only to the negative charges, the electrons.
Is the measure of the capacity of the material to oppose to the flow of electric current and is measured in ohms * meter. Most of the rocks have electrolytic conductivity since, with the exceptions of some metallic minerals, almost all minerals are insulating. Conductivity is therefore essentially due to interstitial water and is a function of porosity, water content and amount of salts dissolved in water. The presence of fluids in the subsoil causes rocks and soils, traversed by the current, to behave relatively like good conductors of electricity.
The set of known electromagnetic radiations is called electromagnetic spectrum and covers a very wide frequency range: from a minimum of 50 Hz, to the frequency of the waves emitted by the current, up to a maximum of 1023 Hz, the frequency of gamma rays. The infrared band (IR) is generally divided into near, middle, far and extreme infrared, and covers the wavelength range between 700nm and 1mm.
The geophone is a sensor capable of detecting the movements of the ground solicited by an earthquake or artificial actions, transforming the received signal into an electrical impulse
The gravitational field is a modification of the space caused by the presence of a mass; any other mass placed in the gravitational field generated by a body is attracted to it. The attraction force between the two masses is proportional to the ratio of the masses and inversely proportional to the square of their distance. Every body in free fall is subject to an acceleration, independent of its mass, which on the earth's surface is equal to 9.81 m / s2
The hydrophone is a sensor capable of detecting acoustic signals in water or other fluids
An inertial measurement unit is an electronic system based on inertial sensors, such as accelerometers and gyroscopes, which allows to define the attitude of an aircraft, ie the roll, yaw and pitch angles.
The infrared or IR radiations emitted by a body is caused by the thermal agitation of atoms and molecules; their intensity and frequency are related to the absolute temperature of the body.
In the vacuum the light moves with a speed equal to 299.792.458 m / s. In the air the speed is lower and differs from that in the vacuum of only 3 parts out of 1000. For both these speeds the approximate value of 300.000 m / s is often used.
Is a measure of how much a material will become magnetized in an applied magnetic field. Mathematically, it is the ratio of magnetization M (magnetic moment per unit volume) to the applied magnetizing field intensity H. This allows a simple classification of most materials' response to an applied magneticThe materials are divided into: Diamagnetic (the material reacts to the H field with a very weak magnetization opposed to H), paramagnetic (the material reacts to the H field with a very weak H-magnetization) and ferromagnetic (the material reacts to the H field with a very strong magnetization in agreement with H). In ferromagnetic substances magnetization can exist even in the absence of external fields.
Reflection, which follows a simple law, occurs at plane boundaries. The angle between the direction of motion of the oncoming wave and a perpendicular to the reflecting surface (angle of incidence) is equal to the angle between the direction of motion of the reflected wave and a perpendicular (angle of reflection).
The phenomenon of refraction occurs when the wave crosses the surface that separates different materials and consists in a change in the direction of propagation. The angle of refraction depends on the angle of incidence and the indices of refraction of the two media. The relationship between these magnitudes is called Snell's law of refraction.
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