DU Ka Unit (Science Unit) key terms

The rate at which an object changes its position in a stated direction, calculated as displacement divided by time. Unlike speed, it includes direction, so a change of direction changes velocity even at constant speed.

The rate at which velocity changes with time, whether by speeding up, slowing down, or turning. Measured in metres per second squared, it is positive for increasing speed and negative for slowing down.

The straight-line distance and direction from an object's starting point to its final point. It is a vector quantity, so a round trip returns a displacement of zero even though distance travelled is not zero.

The rule that the net force on a body equals its mass multiplied by its acceleration. Heavier objects need more force for the same acceleration, and force and acceleration point in the same direction.

A push or pull on an object that can change its motion, shape, or direction. It is measured in newtons and is a vector, so both size and direction matter when forces combine.

Energy transferred when a force moves an object along the direction of that force, calculated as force times displacement. The unit is the joule; a force perpendicular to motion does no work.

The rate at which work is done or energy is transferred, equal to work divided by time. Measured in watts, where one watt is one joule per second, it shows how quickly energy is used.

The capacity of a system to do work, existing in forms such as kinetic, potential, thermal, chemical, and electrical. In a closed system total energy is conserved, though it may change form.

The relationship stating that current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, written as V equals I times R, provided temperature stays constant.

The opposition a material offers to the flow of electric current, measured in ohms. It depends on the material, its length, its cross-sectional area, and its temperature.

The rate of flow of electric charge through a conductor, measured in amperes. One ampere equals one coulomb of charge passing a point each second; conventional current flows from positive to negative.

A scalar is a quantity with magnitude only, such as mass or temperature. A vector has both magnitude and direction, such as force or velocity, and vectors add by geometric rules rather than simple arithmetic.

The amount of substance containing exactly the same number of elementary particles as there are atoms in twelve grams of carbon-12, that number being Avogadro's constant, approximately 6.022 times ten to the twenty-third.

The mass of one mole of a substance, expressed in grams per mole and numerically equal to its relative molecular mass. It converts between mass in grams and amount in moles.

The calculation of quantities of reactants and products in a chemical reaction using the balanced equation. Mole ratios from the coefficients allow prediction of masses, volumes, or concentrations involved.

The reactant that is used up first in a reaction and therefore determines the maximum amount of product formed. Other reactants are said to be in excess and remain partly unreacted.

A measure of solution concentration equal to the number of moles of solute dissolved per litre of solution, written in moles per litre. It changes with temperature because solution volume expands when heated.

An acid donates protons or accepts electron pairs, while a base accepts protons or donates electron pairs. Their reaction produces water and a salt in a neutralisation process.

A scale from zero to fourteen expressing the acidity or alkalinity of a solution as the negative logarithm of hydrogen ion concentration. Values below seven are acidic, seven is neutral, and above seven is basic.

Oxidation is loss of electrons and reduction is gain of electrons; the two always occur together in a redox reaction. Oxidation states of the reacting elements change during the process.

The decomposition of a compound in solution or molten form by passing a direct electric current through it. Positive ions move to the cathode and negative ions to the anode, where products are discharged.

An arrangement of elements in order of increasing atomic number, grouped so that elements with similar chemical properties fall in the same column. Position reveals trends in size, reactivity, and bonding behaviour.

The number of protons in the nucleus of an atom, which uniquely identifies the element. In a neutral atom it also equals the number of electrons surrounding the nucleus.

One of two or more forms of the same element whose atoms have equal proton numbers but different neutron numbers. They share chemical behaviour but differ in mass and sometimes in nuclear stability.

The tendency of an atom in a molecule to attract shared electrons toward itself. It increases across a period and decreases down a group, and large differences between atoms produce ionic bonding.

A chemical bond formed when two atoms share one or more pairs of electrons. It is typically strong and directional, and it occurs mainly between non-metal atoms of similar electronegativity.

An equation in which the highest power of the unknown is two, written in the form a x squared plus b x plus c equals zero with a not zero. It has at most two real roots.

The expression b squared minus four a c in a quadratic equation. Its sign shows the nature of roots: positive gives two distinct real roots, zero gives equal roots, and negative gives no real roots.

A sequence in which each term after the first is obtained by adding a fixed constant called the common difference. Its nth term is a plus n minus one times d, and its sum has a standard formula.

A sequence in which each term after the first is found by multiplying the previous term by a fixed ratio. Terms grow or shrink rapidly depending on whether that common ratio exceeds or falls below one.

A permutation counts ordered arrangements of selected items, while a combination counts selections where order does not matter. The combination count equals the permutation count divided by the factorial of the number chosen.

A number between zero and one expressing how likely an event is, calculated as favourable outcomes divided by total equally likely outcomes. Zero means impossible and one means certain.

The product of all positive integers from one up to a given whole number, written with an exclamation mark. By convention the factorial of zero equals one, and factorials grow extremely fast.

The exponent to which a fixed base must be raised to produce a given number. Logarithms turn multiplication into addition and are the inverse operation of exponentiation.

The total obtained by adding the terms of a sequence, often written with sigma notation. Standard formulas exist for arithmetic and geometric series and for sums of squares and cubes.

The process of writing an expression as a product of simpler factors. For quadratics it often means finding two binomials whose product gives the original expression, which reveals the roots.

The process by which green plants and some other organisms use sunlight, carbon dioxide, and water to make glucose and release oxygen. It occurs mainly in chloroplasts and stores light energy as chemical energy.

The release of energy from glucose by cells, either with oxygen producing carbon dioxide and water, or without oxygen producing lactate or ethanol. It supplies the energy currency used for cellular work.

A protein that speeds up a specific biochemical reaction by lowering its activation energy. Each enzyme has an active site fitting particular substrates, and activity depends on temperature and pH.

A type of cell division producing two daughter cells with the same chromosome number as the parent. It is responsible for growth, repair, and asexual reproduction in body cells.

A reduction division producing four daughter cells, each with half the chromosome number of the parent cell. It occurs in the formation of gametes and creates genetic variation through crossing over and independent assortment.

A thread-like structure of DNA and protein found in the nucleus, carrying genes in a linear order. Humans have forty-six chromosomes in body cells, arranged as twenty-three pairs.

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

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 needs no energy input.

The net movement of particles from a region of higher concentration to one of lower concentration, driven by random motion. It continues until concentrations are equal and requires no energy.

A form of deductive reasoning with two premises leading to a conclusion, such as all A are B and all B are C, therefore all A are C. Validity depends on form, not on actual truth.

A question type that asks you to identify the relationship between one pair of items and apply the same relationship to another pair. The relationship must be consistent in both pairs.

A reasoning task requiring identification of the pattern governing a sequence of numbers, letters, or figures so the next term can be supplied. Patterns may involve differences, ratios, or alternating rules.

Drawing a specific conclusion that must follow from general statements accepted as true. If the premises are true and the reasoning is valid, the conclusion is guaranteed, unlike in inductive reasoning.