Saga Public High School Entrance Examination - Science key terms

How far an object travels in a given amount of time, calculated by dividing distance by time. It tells only how fast something moves, not the direction of that movement.

Speed in a stated direction. Because direction is part of it, a change of direction counts as a change in velocity even when the speed itself stays constant.

The rate at which velocity changes over time, whether the object speeds up, slows down, or changes direction. It is measured in metres per second squared and can be negative when motion slows.

A push or a pull acting on an object, measured in newtons. Forces can change an object's shape, speed, or direction, and several forces acting together can cancel out.

A resisting force that acts between surfaces in contact and opposes sliding or rolling. It converts kinetic energy into heat, and it can be reduced by lubricants or smooth surfaces.

Three rules describing how forces affect motion: objects stay at rest or in uniform motion unless a net force acts; force equals mass times acceleration; and every action has an equal and opposite reaction.

Energy an object stores because of its height above a reference level and its mass. It increases when the object is lifted and is released as motion when the object falls.

The energy an object possesses due to its motion, depending on both its mass and the square of its speed. Doubling the speed gives four times as much kinetic energy.

The principle that energy cannot be created or destroyed, only transferred between objects or changed from one form into another. The total amount in a closed system stays the same.

The flow of electric charge through a conductor, measured in amperes. It requires a complete circuit and a source of electromotive force such as a battery to keep it flowing.

The electrical potential difference between two points in a circuit, measured in volts. It is the push that drives current through components and is supplied by cells or generators.

How strongly a component opposes the flow of electric current, measured in ohms. For a fixed voltage, a larger resistance allows a smaller current to pass.

A magnet produced by winding a coil of wire around an iron core and passing current through it. Its magnetism can be switched off, and its strength grows with more turns or more current.

The region around a magnet or current-carrying wire where magnetic forces can be detected. Field lines run from north to south outside a magnet and never cross one another.

The number of complete waves passing a point each second, measured in hertz. A higher frequency means a shorter wavelength when the wave speed stays the same.

The distance between two matching points on consecutive waves, such as crest to crest, usually measured in metres. It relates to frequency and wave speed by the wave equation.

The maximum displacement of a wave from its resting position. A larger amplitude carries more energy, which is why a louder sound or brighter light has greater amplitude.

The smallest particle of an element that still has that element's properties. It consists of a nucleus of protons and neutrons surrounded by electrons, and atoms combine to form molecules.

A group of two or more atoms joined by chemical bonds, such as water or oxygen gas. Molecules are the smallest units of a compound that keep its chemical identity.

An atom or group of atoms that has gained or lost electrons, giving it a positive or negative charge. Positive ions are called cations and negative ones anions.

A shorthand notation showing which elements a substance contains and in what ratio, using symbols and subscript numbers. For example, H2O shows two hydrogen atoms bonded to one oxygen atom.

A written representation of a chemical reaction using formulas, with reactants on the left and products on the right. It must be balanced so that atoms are conserved.

The rule that the total mass of the substances taking part in a chemical reaction does not change. It explains why chemical equations must be balanced atom by atom.

Acids release hydrogen ions in water and turn blue litmus red; bases release hydroxide ions and turn red litmus blue. They neutralise each other to form a salt and water.

A scale from 0 to 14 expressing how acidic or alkaline a solution is. Values below 7 are acidic, 7 is neutral, and values above 7 are alkaline.

The reaction in which an acid and a base cancel each other's properties, producing a salt and water. The resulting solution is closer to pH 7 than either reactant was.

The smallest unit of life that can carry out all the processes of living things. Cells are bounded by a membrane and contain cytoplasm, and some have a nucleus and organelles.

A specialised structure inside a cell that performs a particular job, such as a mitochondrion releasing energy or a chloroplast carrying out photosynthesis. Different organelles suit different cell functions.

Cell division that produces two genetically identical daughter cells, used for growth and repair. The chromosomes are copied and then separated evenly before the cell splits.

Cell division that halves the chromosome number to produce gametes, each genetically different. When two gametes fuse at fertilisation, the normal chromosome number is restored.

A section of DNA that carries the instructions for one inherited characteristic or protein. Genes occur in pairs in body cells and are passed from parents to offspring.

One of the alternative versions of a gene, such as the tall or short version of a plant-height gene. An organism inherits one allele from each parent, and dominant alleles mask recessive ones.

Describes how alleles interact: a dominant allele shows its effect even when only one copy is present, while a recessive allele shows only when two copies are inherited.

The process by which individuals with inherited features suited to their environment survive and reproduce more successfully, so those features become more common in later generations.

A feature or behaviour of an organism that improves its chance of survival in its habitat. Adaptations arise over many generations through natural selection acting on inherited variation.

The gradual change in inherited characteristics of a population over many generations, often leading to new species. Its main mechanism is natural selection acting on variation.

A sequence showing how energy passes from one organism to another through feeding, starting with a producer. Arrows point from the organism eaten to the organism that eats it.

Producers make their own food by photosynthesis, while consumers obtain energy by eating other organisms. Producers form the base of every food chain and support all consumers above them.

A diagram of many interconnected food chains in an ecosystem, showing that most organisms eat several kinds of food. It is more realistic than a single chain and shows feeding relationships in a community.

The process by which green plants use light energy to convert carbon dioxide and water into glucose and oxygen. It takes place in chloroplasts and supplies the energy for nearly all food chains.

Weather is the day-to-day state of the atmosphere, while climate is the average pattern of weather over many years. A single cold day does not change a region's climate.

The force exerted by the weight of air pressing on a surface, measured with a barometer. Air moves from high-pressure to low-pressure areas, producing winds.

Rock formed when molten magma or lava cools and solidifies, either underground or at the surface. Its crystals are large if cooling was slow and small if it was rapid.

Rock formed from layers of sediment that are compacted and cemented over long periods, often containing fossils. Examples include sandstone and limestone, which may show visible strata.

Rock changed by intense heat or pressure deep underground, which alters its texture and mineral structure without melting it. Marble formed from limestone is a common example.

The spinning of Earth on its own axis once roughly every 24 hours, which causes day and night. It also makes the Sun and stars appear to move across the sky.

The orbit of Earth around the Sun, taking about one year, combined with a tilted axis. This produces the cycle of the seasons and changes the length of daylight.