OCR GCSE Combined Science A key terms

The overall movement of particles in one direction, after taking movement in both directions into account.

The overall resistance of a combination of components, considered as a single resistance.

A nerve cell specialised to carry electrical impulses.

Having zero net electric charge.

An atom with equal numbers of positively charged protons and negatively charged electrons, giving it no overall electrical charge.

A reaction between an acid and a base. When an acid reacts with an alkali, hydrogen ions react with hydroxide ions to form water.

The condition in which a solution has equal concentrations of hydrogen ions and hydroxide ions. At room temperature, its pH is approximately 7.

A solution that is neither acidic nor alkaline, with a pH of 7.

The mains wire that completes the operating circuit back to the supply. It is close to earth potential and has blue insulation.

A particle in an atom’s nucleus with no electrical charge and relative mass approximately 1.

The unit of force. A resultant force of 1 N gives a mass of 1 kg an acceleration of $1\text{ m/s}^2$.

An instrument used to measure force in newtons, commonly using the stretching of a spring.

An object remains at rest or continues moving with constant velocity unless acted on by a non-zero resultant force.

The relationship between resultant force, mass and acceleration: $F = ma$. Acceleration is in the direction of the resultant force.

Whenever two objects interact, they exert equal and opposite forces on each other.

The movement of nitrogen between organisms and non-living stores such as the atmosphere and soil.

Gases containing nitrogen and oxygen, often written collectively as $\mathrm{NO_x}$, formed when nitrogen and oxygen react at high temperatures.

A very unreactive, colourless gaseous element in Group 0.

A solvent other than water, such as hexane.

A disease that cannot be transmitted between organisms, even if an infection contributed to its development.

A force that acts between objects without them touching, such as the attraction or repulsion between magnets.

A system in which substances can enter or leave the material being studied, for example through the opening of a flask.

A metal other than iron, such as copper or aluminium.

An electrode whose material takes part in an electrolysis reaction; also called an active electrode.

A circuit component whose current–potential difference graph is not a straight line over the range being considered.

A relationship represented by a graph that is not a straight line: its gradient changes.

An element that typically conducts heat and electricity poorly and is brittle when solid. Non-metal atoms can gain electrons to form negative ions or share electrons when bonding.