SITEEE key terms

The net force on a body equals the rate of change of its momentum; for constant mass this is written F = ma, so acceleration points along the net force and is inversely proportional to mass.

The total work done by all forces acting on a particle equals the change in its kinetic energy, allowing speed changes to be found from force and displacement without analysing time.

When no net external force acts on a system, its total linear momentum remains constant because internal forces occur in equal and opposite pairs, so collisions and explosions conserve momentum.

A body's resistance to angular acceleration about a chosen axis, equal to the sum of mass times the square of distance from the axis for all its particles; it depends on axis and mass distribution.

Oscillation in which the restoring acceleration is proportional to displacement from equilibrium and directed toward it, producing sinusoidal motion whose period does not depend on amplitude.

The junction rule states that charge entering a node equals charge leaving it; the loop rule states that potential differences around any closed circuit loop sum to zero, both resting on conservation laws.

The emf induced in a circuit equals the negative rate of change of magnetic flux through it; the minus sign, Lenz's law, means the induced current opposes the change producing it.

When light travels from a denser to a rarer medium at an angle beyond the critical angle, it is entirely reflected back inside instead of refracting out; optical fibres rely on this.

The emission of electrons from a metal surface struck by light of frequency above a threshold value, regardless of intensity; it shows light delivers energy in discrete quanta called photons.

If a system at equilibrium is disturbed by a change in concentration, pressure or temperature, the position of equilibrium shifts in the direction that partially counteracts that disturbance.

The mixing of atomic orbitals of comparable energy on the same atom to give an equivalent set of hybrid orbitals, which explains observed molecular shapes and bond angles.

A measure of how strongly an atom attracts the shared electron pair of a covalent bond; differences between bonded atoms create polar bonds and decide whether a bond is mainly ionic.

A solution that resists large pH changes when small amounts of acid or base are added, typically made from a weak acid with its conjugate base or a weak base with its conjugate acid.

The enthalpy change when one mole of a compound is formed from its elements in their standard states at 298 K and 1 bar; these values are combined through Hess's law to find reaction enthalpies.

A bookkeeping charge assigned to an atom by assuming bonding electrons belong entirely to the more electronegative partner; changes in it identify oxidised and reduced species in redox reactions.

A planar, cyclic, completely conjugated ring is aromatic when it contains 4n + 2 pi electrons; rings with 4n electrons are antiaromatic, and non-conjugated or non-planar rings are not aromatic.

Solution properties that depend on the number of dissolved particles rather than their identity: vapour-pressure lowering, boiling-point elevation, freezing-point depression and osmotic pressure, all measurable for molar mass determination.

A scalar computed from a square matrix that signals whether the matrix can be inverted; it is nonzero exactly when the rows and columns are linearly independent.

The value a function's output approaches as the input approaches a specified point, whether or not the function is defined there; limits are the foundation of continuity and differentiation.

A function is continuous at a point when it is defined there, the limit at that point exists, and the limit equals the function's value; otherwise it has a removable, jump or infinite discontinuity.

The instantaneous rate of change of a function with respect to its variable, defined as the limit of a difference quotient; geometrically it gives the slope of the tangent line.

The limit of a sum of signed areas between a curve and the x-axis over an interval; the fundamental theorem evaluates it using any antiderivative of the integrand.

The probability that event A occurs given that event B has already occurred, written P(A|B) = P(A ∩ B)/P(B) with P(B) > 0; it revises likelihood using known information.

A selection of objects in which arrangement does not matter; the number of ways to choose r objects from n distinct objects is n! divided by r!(n − r)!.

For a conic, the ratio of the distance of a point from the focus to its distance from the directrix; below 1 gives an ellipse, exactly 1 a parabola, above 1 a hyperbola.

For a complex number z = a + bi, the conjugate is a − bi; multiplying the two gives the real number a² + b², which is used to divide complex numbers and find moduli.

If a function is continuous on a closed interval, differentiable inside it and takes equal values at both endpoints, then its derivative vanishes at some interior point.

Division of a eukaryotic nucleus that produces two daughter cells with the same chromosome number as the parent, underlying growth, tissue repair and asexual reproduction.

Two successive nuclear divisions that halve the chromosome number and reshuffle genes through crossing over and independent assortment, producing haploid gametes or spores.

The light-driven manufacture of carbohydrate from carbon dioxide and water inside chloroplasts, releasing oxygen; the light reactions supply ATP and NADPH for the Calvin cycle.

The synthesis of an RNA copy of a DNA segment by RNA polymerase, which reads the template strand and adds ribonucleotides to the growing RNA chain in the 5′ to 3′ direction.

The unequal survival and reproduction of individuals whose heritable variations suit the environment better, which gradually alters allele frequencies in a population over successive generations.

The net movement of water across a semipermeable membrane from a region of higher water potential to lower water potential, driven by differences in solute concentration.

A biological catalyst, usually a protein but sometimes RNA, that speeds a specific reaction by lowering its activation energy while binding substrates at a shaped active site without being consumed.

The maintenance of a steady internal environment around a set point by negative feedback loops that sense deviations and trigger corrective physiological responses.

Adenosine triphosphate, the universal energy carrier of cells; hydrolysis of its terminal phosphate bond releases free energy that drives endergonic reactions, active transport and mechanical work.

The particular set of alleles an organism carries for one gene or for many genes together, which interacts with the environment to produce the observable phenotype.