Akita Entrance Science key terms

The rate at which an object's position changes in a stated direction, expressed as displacement divided by time. Because direction is included, it differs from speed, which has magnitude only.

The rate at which velocity changes with time, including speeding up, slowing down, or changing direction. It is measured in metres per second squared and is caused by a net force.

The rule that the net force on an object equals its mass multiplied by its acceleration (F = ma). A larger force or smaller mass produces a greater acceleration in the direction of the net force.

The single combined effect of all forces acting on an object, found by adding them as vectors. If the net force is zero, the object's motion does not change.

A contact force that opposes relative sliding or attempted sliding between surfaces. It converts kinetic energy into thermal energy and depends on the surfaces and the normal force.

The energy an object possesses because of its motion, calculated as one half of mass times speed squared. Doubling the speed quadruples the kinetic energy.

Stored energy that depends on an object's position or configuration, such as height in a gravitational field or stretch in a spring. It can be converted into kinetic energy.

The principle that energy cannot be created or destroyed, only transferred or transformed between forms. In a closed system the total energy stays constant, though some may spread as heat.

The number of complete wave cycles passing a fixed point each second, measured in hertz. Frequency is inversely related to wavelength for waves travelling at a fixed speed.

The distance between two consecutive corresponding points on a wave, such as crest to crest. It is inversely proportional to frequency when wave speed is constant.

The bending of a wave as it passes from one medium into another where its speed differs. The change in speed causes a change in direction unless the wave enters along the normal.

The rate of flow of electric charge through a conductor, measured in amperes. It requires a complete circuit and is driven by a potential difference.

The potential difference between two points in a circuit, measured in volts. It represents the energy transferred per unit charge and is what pushes current through a conductor.

A measure of how strongly a component opposes the flow of electric current, measured in ohms. For a fixed voltage, higher resistance means less current.

The smallest unit of an element that retains that element's chemical properties. It consists of a nucleus of protons and neutrons surrounded by electrons.

An atom or group of atoms that has gained or lost electrons, giving it a net electrical charge. Positive ions form when electrons are lost and negative ions when they are gained.

A chemical bond formed when two atoms share one or more pairs of electrons. It typically joins non-metal atoms and produces molecules rather than charged lattices.

The electrostatic attraction between oppositely charged ions, usually a metal cation and a non-metal anion. It forms a lattice of alternating charges rather than discrete molecules.

Two or more atoms held together by covalent bonds, forming the smallest unit of a substance that keeps its composition. Water and carbon dioxide are common examples.

The amount of a substance containing 6.02 x 10^23 representative particles, known as Avogadro's number. 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, found by summing atomic masses. It converts between mass and moles in stoichiometric calculations.

The reactant that is used up first in a chemical reaction and therefore determines the maximum amount of product formed. Others are left over in excess.

A scale from 0 to 14 describing the concentration of hydrogen ions in a solution. Values below 7 are acidic, 7 is neutral, and above 7 is basic.

The reaction between an acid and a base that produces a salt and water. The hydrogen ions of the acid combine with the hydroxide ions of the base.

A process in which a substance loses electrons, often by gaining oxygen or losing hydrogen. It always occurs together with reduction in a redox reaction.

A process in which a substance gains electrons, often by losing oxygen or gaining hydrogen. It is the partner process to oxidation in any redox reaction.

A substance that increases the rate of a reaction by providing a lower-energy pathway, without being consumed. It does not change the overall energy released or the equilibrium position.

The minimum energy colliding particles need for a reaction to occur. A catalyst lowers this barrier, so more collisions succeed and the reaction proceeds faster.

A thin, selectively permeable layer of phospholipids and proteins surrounding a cell. It controls which substances enter and leave and separates the cell from its surroundings.

The net movement of particles from a region of higher concentration to a region of lower concentration, driven by random motion. It requires no energy input from the cell.

The movement of water molecules across a partially permeable membrane from a region of higher water concentration to one of lower water concentration. It is passive and important for cell water balance.

A protein that speeds up a specific biochemical reaction by lowering its activation energy. Its activity depends on temperature and pH because its shape can be altered.

The process in which plants use light energy to convert carbon dioxide and water into glucose and oxygen. It occurs mainly in chloroplasts and stores energy in chemical bonds.

The series of reactions in cells that release energy from glucose, using oxygen in aerobic cases and producing carbon dioxide and water. The energy is captured in ATP.

The green pigment in chloroplasts that absorbs mainly red and blue light for photosynthesis. It reflects green light, which is why most leaves look green.

A type of cell division producing two genetically identical daughter cells, used for growth and repair. Chromosomes are copied and separated before the cell splits.

A two-stage cell division that produces four genetically varied gametes, each with half the normal chromosome number. It creates variation through independent assortment and crossing over.

One of the alternative versions of a gene found at the same position on a chromosome. An organism's combination of alleles determines the traits it expresses.

The observable characteristics of an organism, resulting from its genotype interacting with the environment. Two organisms with the same phenotype may have different genotypes.

The process by which individuals with traits better suited to their environment tend to survive and reproduce more, so those traits become more common over generations.

The theory that Earth's rigid outer shell is broken into plates that move slowly over the mantle. Their interactions cause earthquakes, volcanoes, and mountain building.

A boundary where two tectonic plates move toward each other. Oceanic crust may subduct beneath another plate, forming trenches and volcanic arcs, or continents may collide to raise mountains.

The shaking of the ground caused by a sudden release of stored elastic energy along a fault. Its location and size are recorded by seismographs.

The set of processes that transform igneous, sedimentary, and metamorphic rock into one another through melting, cooling, weathering, burial, and heat and pressure.

The breakdown of rock in place by physical, chemical, or biological processes. The resulting fragments can later be eroded and transported to form sediment.

Rock formed when layers of sediment are compacted and cemented over time. It often contains fossils and shows distinct bedding, unlike igneous or metamorphic rock.

The warming of a planet's surface because certain atmospheric gases absorb and re-emit outgoing infrared radiation. Without it Earth would be far colder than it is.

The fraction of incoming solar radiation reflected by a surface. Ice and snow have high albedo, while oceans and forests have low albedo and absorb more energy.

The process in which a collapsing cloud of gas and dust formed a rotating disk, with the Sun condensing at the centre and planets accreting from the surrounding material.

The attractive force between any two objects with mass, increasing with mass and decreasing with distance. It keeps planets in orbit and causes objects to fall toward Earth.

A testable, specific prediction about the relationship between variables, stated before data are collected. A good hypothesis can be supported or rejected by evidence.

The factor that the experimenter deliberately changes or selects in an investigation. Its effect is observed by measuring the dependent variable.

The factor that is measured or observed in an experiment, expected to respond to changes in the independent variable. It provides the data used to judge the hypothesis.

A factor kept constant across all trials so that it cannot affect the outcome. Holding such factors constant makes it possible to attribute changes to the independent variable.

A comparison group that does not receive the experimental treatment and is otherwise treated identically. It shows what would have happened without the change being tested.

The consistency of a measurement when it is repeated under the same conditions. Taking repeated readings and averaging them generally improves reliability.

How close a measured value is to the true value. It is improved by calibrating instruments and correcting systematic errors, not simply by repeating measurements.

The difference between a measured value and the true value, arising from instrument limits, technique, or random variation. It can be reduced but never entirely eliminated.

A simplified representation of a system or process used to explain observations and make predictions. Models are always approximations and are revised when evidence contradicts them.

A concise statement, often mathematical, describing a consistent pattern observed in nature without explaining why it occurs. It can be used to predict outcomes of similar situations.