**speed up:**action of changing the speed of in one motion.**acoustics:**Part of physics that deals with sounds and related phenomena. Determination of harmonic interval ratios by discovering the properties of vibrating strings.**adiabata:**is the name given to the curve of the volume pressure diagram that expresses an adiabatic transformation, that is, with the amount of heat of the gas conserved.**adiabatic:**Thermodynamic transformation that takes place without the body or system losing or gaining any amount of heat. Coordinate curve, selected to represent pressure and volume or temperature and entropy of matter during an adiabatic process.**altitude:**Upright height of a place above sea level.**height:**Perpendicular distance from bottom to top; depth; thickness.**2**Distance between the lowest point and the highest point of something upright.**ampere:**Practical unit of electrical measurement corresponding to the intensity of an electric current that, with the electromotive force of 1 volt, travels a circuit with a resistance of 1 ohm.**ammeter:**Instrument for measuring electric current.**angstrom:**It is the measure commonly used to deal with quantities of the order of the atom or the spacings between two crystalline planes. 1 Å = 10^{-10}m**angle:**Figure formed by two straight lines starting from the same point.**anion:**Negatively charged ion.**light-year:**Astronomical length unit: distance traveled by light in one year. Approximately 9,463 x 10^{12}km.**approximation:**Calculation, not absolutely accurate, but as close as possible.**atmosphere:**Gaseous sphere that surrounds the Earth, consisting essentially of oxygen and nitrogen. Gas pressure unit equal to the pressure exerted by a vertical column of mercury, 76 cm high and 1 cm^{2}at 0 ° C at sea level. 1 atm. = 1.033 kg / cm^{2}.**friction:**Resistance that one body develops when another body moves over it. Friction.