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Kostas UŠPALIS ON THE AMBIGUOUS USE OF PHYSICS TERMS For a scientific term to be good and convenient to use, it must be unambiguous, linguistically correct, correspond as closely as possible to the content of the concept, and be short, euphonious, etc. The most important feature of a good term is its unambiguity: one term must correspond to one concept, and each term must describe only one concept (concept ⇄ term). In contrast to the language of belles-lettres, synonymy in terminology is not an advantage but a drawback. Clearly, for a term to be entirely good, unambiguity alone is not enough; it must also meet the other requirements mentioned. But even if the other requirements are met, an ambiguous term is a bad one—it cannot properly fulfil its purpose and may sometimes cause confusion. Conversely, an unambiguous term, even if it is of poor quality in other respects, can be used as a last resort without causing any confusion. Nevertheless, quite a few basic physics terms are often used ambiguously by us, especially when they are used in several branches of science. I will mention a few basic physics terms that are used ambiguously and consider ways to avoid this ambiguity. Characteristic, an international word, is often used by physicists in at least several senses: description, characteristic quantity, characteristic dependence (curve), etc. Here, the polysemy can be avoided by using a Lithuanian term that corresponds to the intended meaning. Characteristic might perhaps be used in only one, most widespread sense—that of a characteristic curve (for example, volt-ampere characteristic). Power. It should be used only in the sense of work done per unit time (change in energy per unit time). To describe the ability of some device or material, the term capacity should be used (the two terms are distinguished in all languages), e.g., absorptivity, reflectivity, resolving power. Speed should be used only in the sense defined from the very beginning of physics instruction at school—the distance travelled per unit time. To describe the rate of various phenomena, the term rate should be used; if the phenomenon is periodic, the term frequency should be used. 41 Impulse is the product of a physical quantity and the time interval during which the action described by that quantity takes place, e.g., force impulse, current (intensity or voltage) impulse, light pulse, sound pulse. It is incorrect to call momentum (mv or E/c) an impulse. Only the change in momentum is equal to the impulse of the force that caused that change. Concentration is the ratio of the amount of an independent component (constituent) of a system (mixture, solution, alloy) to the amount of the entire system. It is expressed as a percentage. It is a dimensionless quantity. Recently, in solid-state physics and even in secondary-school textbooks, we have begun to confuse it with particle (number) density—the number of particles per unit volume, a dimensional quantity. Modulus is a physical quantity describing the deformation of a body—the proportionality coefficient between the deformation of the body (elongation, angle) and the force deforming it (the reciprocal of the deformation coefficient), e.g., elastic (Young’s) modulus, shear modulus, torsion modulus. When one says modulus of force, modulus of pressure, it should be understood that the deformation caused by that force or pressure is meant. The term modulus, borrowed from mathematicians and referring to the magnitude (algebraic, complex, or vector), should not be used in physics literature (secondary-school textbooks) instead of absolute value of a quantity. It should be noted that in other branches of science (construction engineering, electronics) the term modulus has other meanings as well, but they should not be used in physics. Moment. This is the product of a physical quantity and some power of the distance from a reference point (ORn). E.g., moment of force rF, moment of momentum rp, electric dipole moment er, moment of inertia mr2 (second moment of mass). The expression time moment is also often used. According to the general meaning of moment, this should be the product of time and distance, tr. But time moment is used to mean a very short period or a point on the time axis. The term should not be used in physics with these meanings. A short period should be called an instant, and a point on the time axis simply time. For example, instead of saying at the initial moment, one should say at the initial time, at the beginning, at the moment of firing—at the time of firing (for an instant), momentarily—instantaneously (suddenly). Transition is a change in the state of a system. This is an ineuphonious and polysemous term. FTŽ suggests replacing it, according to the meaning, with three terms— 42 sions: 1) surface – when the aggregate state of a system or its principal properties change, 2) jump – when the state of a system (particle) changes very abruptly (instantaneously), so that the duration of the change is negligible, 3) interface – a small region between regions of differing conductivity (in semiconductor physics). Radius. This is a very common word both in everyday language and as a scientific term. But it is ambiguous: 1) in geometry, it is the distance from the center; 2) in physics, it is emitted light (a stream of photons). Usually, the meanings are easily distinguished from the context. But sometimes they cause difficulties when radius is used in both senses in the same sentence. For example: Small-radius stars (dwarfs) emit more short-wavelength rays than large-radius stars (giants), or When an electron jumps between small-radius orbits closer to the nucleus, shorter rays are emitted. Of course, ambiguity here can be avoided by replacing radius in the geometrical sense with another word, and expressing the physical meaning of “shorter rays” as “light of shorter wavelengths.” Still, it would be better if we had another term for the geometric radius, for example, spoke, as was once proposed. Structure. Physicists often use this international term in two senses: 1) a particular item under investigation (object) – an entity, a specimen; 2) the way the item under investigation is put together – composition. Therefore, to avoid ambiguity, it is better to use the Lithuanian terms entity and composition. The examples given show that quite different quantities with different dimensions are often referred to by the same term, for example: velocity and speed, power and capacity, concentration and density, a point in time and the moment of a physical quantity. These are the simplest examples of ambiguous terminology. Many more uncertainties arise from ambiguous terms when describing more complex concepts in specialized fields, especially those borrowed from or translated out of other languages. Authors and translators of textbooks (especially those for secondary schools) should pay more attention to ambiguous terminology and consult more often with terminology specialists—physicists and linguists. 43