Keywords

Unit 5 Solids, Liquids and Gases - Keywords and Mixed Definitions

KEYWORD	DEFINITION
Density (g/cm3) or (kg/m3)	The mass, in kilograms, of one metre cubed of a substance.
Diffusion	Molecules moving from an area of high concentration to an area of low concentration.
Fluid	Any liquid or gas.
Mass (kg)	Amount of material in an object, measured in kilograms.
Pressure (Pa) or (N/m2)	The effect of a force spread out over an area.  Pressure = force / area.  p = F / A.
Brownian motion	The slow, random motion of large, visible particles such as smoke particles.  Explained by postulating much smaller, faster particles that are not visible, such as air particles, that collide with the large particles and make them move.
Kinetic Theory / Particle Model	A model of solids, liquids and gases that explains the observed properties of the materials by postulating that they are made up from lots of tiny, hard, incompressible spheres.  At higher temperatures the spheres move faster.
Kelvin (K)	The units of absolute temperature.  273K = 0oC.
Volume	The space occupied by an object in three dimensions, measured in m3. For cuboids, V = l x h x w.
Absolute Zero	The lowest possible temperature.  0K = -273oC.
Rigid Container	A container that will keep a fixed shape regardless of the pressure inside or outside it.  The volume is constant and the pressure is variable.  Examples are rigid metal cans and glass bottles.
Flexible Container	A container that changes its shape depending on the pressure inside or outside it.  The volume is variable and the pressure is constant.  Examples are syringes and pistons.
Ideal gas	A theoretical model of a gas that describes gas molecules by using the Kinetic Theory.  The molecules are assumed to collide elastically with the walls of the container they are in.