Hokkaido Entrance Science key terms

In a system with no net external force, the total momentum vector stays constant before and after any collision or explosion. This lets you solve two-dimensional collision problems where kinetic energy alone is not conserved.

When only gravity and elastic forces do work, the sum of kinetic and potential energy stays constant. Friction and other non-conservative forces remove mechanical energy, converting it mainly into heat.

Motion at constant speed along a circle. The velocity direction changes continuously, so a centripetal acceleration v squared over r points toward the centre and the net force equals mv squared over r.

Oscillation in which the restoring force is proportional to displacement and points back toward equilibrium. Displacement follows a sine curve, and the period depends on mass and the force constant, not on amplitude.

Relates the angles of incidence and refraction when light crosses a boundary: n1 sin theta1 equals n2 sin theta2. Travelling from a denser to a rarer medium, the ray bends away and may undergo total internal reflection.

Overlapping coherent waves add together, giving bright and dark fringes where the path difference equals a whole or half number of wavelengths. This underlies Young's double-slit and thin-film problems.

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation. Like charges repel and unlike charges attract along the joining line.

A changing magnetic flux through a circuit induces an electromotive force. Faraday's law gives its magnitude, and Lenz's law states that the induced current opposes the change that produced it.

The energy needed to raise the temperature of one gram of a substance by one kelvin. Water's unusually large value explains why it heats and cools slowly, which moderates climate and body temperature.

The change in observed frequency when a source and an observer move relative to each other. Approach raises the observed frequency and recession lowers it; the sign of each velocity term depends on direction.

The amount of substance containing 6.02 times ten to the twenty-third particles. It connects mass, molar mass and gas volume at standard conditions, forming the basis of all stoichiometric calculation.

A reaction in which electrons transfer between species. Oxidation is loss of electrons and a rise in oxidation number; reduction is gain. Balancing uses electron counts or ion-electron half-equations.

The state of a reversible reaction in which forward and reverse rates are equal and concentrations remain constant. The equilibrium constant K depends on temperature only, not on initial amounts or pressure.

When a system at equilibrium is disturbed by a change in concentration, pressure or temperature, it shifts in the direction that partly cancels the change. A catalyst alters only the rate, not the position.

A solution of a weak acid with its conjugate base, or a weak base with its conjugate acid, that resists pH change when small amounts of strong acid or strong base are added.

Driving a non-spontaneous reaction with an external voltage. Oxidation occurs at the anode and reduction at the cathode; the products depend on the discharge order of ions and on the electrode material.

A carboxylic acid and an alcohol react under acid catalysis with heating to give an ester and water. The reaction is reversible, so removing the water shifts it toward the products.

Two molecules with the same connectivity but non-superimposable mirror images, usually because a carbon bears four different groups. The pair rotates plane-polarised light in opposite directions.

Properties of a dilute solution that depend on the number of dissolved particles rather than their identity: vapour pressure lowering, boiling point elevation and freezing point depression.

Plants use light energy in the thylakoid membranes to split water, produce ATP and NADPH, and release oxygen. The Calvin cycle then fixes carbon dioxide into carbohydrate.

Stepwise oxidation of glucose through glycolysis, the Krebs cycle and the electron transport chain, capturing energy as ATP. Oxygen is the final electron acceptor in aerobic cells.

Two successive divisions producing four haploid cells from one diploid cell. Crossing over in prophase I and independent assortment in metaphase I generate genetic variation in the gametes.

An organism carries two alleles for each gene, and these separate during gamete formation, so each gamete receives only one of the pair. This explains the ratios seen in monohybrid crosses.

Each parental strand acts as a template, so every new DNA molecule has one old and one new strand. Helicase unwinds the double helix and DNA polymerase adds nucleotides in the five-prime to three-prime direction.

RNA polymerase copies a DNA template into messenger RNA; ribosomes then read each three-base codon and assemble amino acids into a polypeptide, with transfer RNA delivering the matching amino acids.

A cluster of genes transcribed together from one promoter and regulated as a single unit. The lac operon is switched on by lactose and switched off when glucose is readily available.

A control mechanism in which a deviation from a set point triggers a response that reduces that deviation. It keeps body temperature, blood glucose and water balance within narrow limits.

A rapid reversal of membrane potential that travels along a neuron. Sodium channels open for depolarisation, potassium channels restore the resting potential, and the impulse propagates without losing amplitude.

The lithosphere is broken into rigid plates that move over the asthenosphere. Divergent, convergent and transform boundaries explain earthquakes, volcanoes, mountain belts and deep ocean trenches.

Body waves radiated by an earthquake. P waves are longitudinal and pass through solids and liquids; S waves are transverse, slower, and cannot travel through liquid, revealing the outer core's liquid state.

As magma cools, minerals crystallise in a sequence starting with high-temperature ones and are separated from the remaining melt. The residual magma becomes richer in silica and changes composition.

In an undisturbed sequence of sedimentary layers, younger layers lie above older ones. Combined with cross-cutting relationships and fossil succession, it gives the relative ages of rocks.

Planets move on ellipses with the Sun at one focus; the radius vector sweeps equal areas in equal times; and the square of the orbital period is proportional to the cube of the semi-major axis.

An apparent force caused by Earth's rotation that deflects moving air and water to the right in the Northern Hemisphere and to the left in the Southern, shaping prevailing winds and ocean currents.

Boundaries between air masses. At a warm front, warm air rides gently over cold air, giving wide cloud sheets and steady rain; at a cold front, steep lifting produces narrow bands of heavy showers.

A plot of stellar luminosity against surface temperature or spectral class. Most stars lie on the main sequence, while giants, supergiants and white dwarfs occupy separate regions reflecting different evolutionary stages.