Valencian Community PAU General Sciences key terms

Any property of a body or system that can be measured and expressed as a number plus a unit, such as length, mass, time or temperature.

One of the seven base units agreed internationally (metre, kilogram, second, ampere, kelvin, mole, candela) from which all other units are derived by multiplication and division.

Technique of checking an equation by comparing the base dimensions of both sides; if the dimensions differ, the formula must be wrong, though matching dimensions do not prove it right.

The difference between a measured value and the true value, arising from the instrument's resolution, the observer, or random fluctuations; reported as absolute or relative uncertainty.

The digits of a measurement that carry real information, counted from the first non-zero digit; they show the precision of the instrument and set how many digits a result may keep.

Writing a number as a coefficient between 1 and 10 multiplied by a power of ten, which keeps significant figures clear and makes very large or very small quantities easy to compare.

The nearest power of ten to a quantity, used for quick comparison; two values differ by one order of magnitude when one is roughly ten times the other.

Motion along a straight line at constant velocity, so acceleration is zero and position changes linearly with time according to x = x0 + vt.

Straight-line motion with constant non-zero acceleration; velocity changes linearly with time and position quadratically, as in free fall near the Earth's surface.

Treating a two-dimensional motion as the superposition of independent motions along each axis, as in projectile motion where horizontal velocity is constant and vertical motion is accelerated.

The net force directed towards the centre of a circular path that keeps a body turning; its magnitude is mv²/r and it changes direction of velocity, not speed.

Newton's law stating that two point masses attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.

Energy stored because of a body's position in a gravitational field; near the Earth it equals mgh, while in general it is taken as -GMm/r.

Principle that the sum of kinetic and potential energy stays constant when only conservative forces act; with friction, part of it is transferred as heat.

Work is the energy transferred by a force along a displacement (W = F·d·cosθ); power is the rate of doing work, measured in watts.

The restoring force of an ideal spring is proportional to its extension and opposite in direction: F = -kx, where k is the spring constant in N/m.

Oscillation where acceleration is proportional to displacement and directed towards equilibrium; position follows a sine or cosine with fixed amplitude, period and phase.

A disturbance that transfers energy through space without transporting matter; described by amplitude, wavelength, frequency and speed, and classified as mechanical or electromagnetic, transverse or longitudinal.

Change in direction and speed of a wave when it passes from one medium to another with a different propagation speed, governed by Snell's law and the refractive indices involved.

The figure formed where rays converge (real) or from which they appear to diverge (virtual); located with the thin-lens or mirror equation using focal length and object distance.

Region around a charge where another charge experiences a force; the field vector at a point equals force per unit positive charge and points away from positive charges.

Electric potential energy per unit positive charge at a point, measured in volts; it is a scalar and equals the work needed to bring a unit charge from infinity.

For a conductor at constant temperature, current is proportional to potential difference across it: V = IR, where resistance is measured in ohms.

Generation of an electromotive force in a circuit when the magnetic flux through it changes, as described by Faraday's law and Lenz's law on the direction of the induced current.

Spontaneous emission of alpha, beta or gamma radiation from unstable nuclei as they decay towards stability; the activity falls exponentially with a characteristic half-life.

Fission splits a heavy nucleus into lighter ones, releasing energy; fusion joins light nuclei into a heavier one. Both convert a small mass defect into large amounts of energy.

The SI amount-of-substance unit, containing exactly 6.022×10²³ elementary entities; it links the mass of a sample to the number of particles it contains.

The mass of one mole of a substance in grams per mole, numerically equal to its relative molecular mass; used to convert between mass and moles.

Avogadro's number is 6.022×10²³ particles per mole; stoichiometry uses balanced equations and mole ratios to calculate masses, volumes or amounts of reactants and products.

The reactant that is used up first in a reaction and therefore fixes the maximum amount of product formed; the others remain partly unused in excess.

The actual mass of product obtained divided by the theoretical maximum, expressed as a percentage; values below 100% reflect side reactions, losses or incomplete conversion.

A homogeneous mixture of solute in solvent; concentration expresses how much solute is present per volume or mass, commonly as molarity (moles per litre).

An acid donates protons and a base accepts them (Brønsted) or they exchange electron pairs (Lewis); their reaction produces a salt and often water.

pH is the negative logarithm of hydrogen-ion concentration, so 7 is neutral at 25 °C; neutralisation is the reaction of an acid with a base to give salt and water.

Reaction in which electrons are transferred: the species that loses electrons is oxidised and acts as reducing agent, while the one that gains them is reduced.

The force holding atoms together in compounds: ionic by electron transfer, covalent by sharing pairs, and metallic by a shared sea of delocalised electrons.

The three-dimensional arrangement of atoms around a central atom, predicted from electron-pair repulsion (VSEPR) and determining properties such as polarity.

The ordered sequence of growth, DNA replication and division by which one cell gives two genetically identical daughter cells with the same chromosome number.

Two successive divisions producing four haploid cells, with crossing-over and independent assortment of chromosomes generating genetic variation in gametes.

DNA is a double helix of nucleotides whose sequence stores genetic information; replication copies it semi-conservatively before cell division.

Inheritance model based on discrete alleles: dominant and recessive traits, segregation of alleles in gametes, and independent assortment of genes on different chromosomes.

A permanent change in the DNA sequence, which may be silent, alter a protein, or affect regulation; it is the original source of new alleles in populations.

The set of chemical reactions in a cell, split into catabolism that releases energy by breaking molecules down and anabolism that consumes energy to build them.

Photosynthesis uses light energy to fix carbon dioxide into organic matter, releasing oxygen; respiration oxidises organic molecules to obtain ATP, carbon dioxide and water.

A community of organisms plus its physical environment; energy enters through producers and passes along trophic levels, losing most of it as heat at each step.

Theory that the lithosphere is divided into rigid plates moving over the asthenosphere, explaining earthquakes, volcanoes, mountain belts and the distribution of continents.

The continuous transformation of igneous, sedimentary and metamorphic rocks through melting, cooling, weathering, transport, deposition and metamorphism.

Erosion wears away and transports rock material by water, wind or ice; sedimentation deposits it in layers that may later harden into sedimentary rock.

The probability that a geological hazard such as an earthquake, landslide or volcanic eruption causes damage, combining the hazard with the vulnerability of exposed people and assets.

Cycle of observing a problem, forming a testable hypothesis, designing controlled experiments, analysing data and revising the hypothesis in the light of evidence.

A hypothesis is a falsifiable proposed explanation; variables are the factors measured (dependent) or deliberately changed (independent) while others are held constant.

A control group receives no treatment so the effect of the variable can be isolated; reproducibility means independent repetitions give consistent results under the same conditions.