 # GCSE Physics # Matter - Equations and Definitions density (kg/m3) = mass (kg) / volume (m3) pressure due to a column of liquid (Pa) = height of column (m) × density of liquid (kg/m3) × gravitational field strength (N/kg) pressure (Pa) × volume (m3) = constant (for a given mass of gas and at a constant temperature)

Model - a theoretical construction, idea, explanation or analogy which helps us to explain processes.

Electron - a subatomic particle with a charge of -1 and mass in the order of 1/1800 a single proton.  (In standard units its mass is 9.11×10-31kg and its charge is -1.6×10-16C.)

Proton - a subatomic particle with a charge of +1 and mass 1u.  (A u is the unified atomic mass unit and is equal to 1.7×10-27kg, its charge is 1.6×10-16C.)

Neutron - a subatomic particle with a charge of 0 and mass 1u.

Plum-pudding model -  a model prevalent in the early twentieth century which explained the atom as having uniformly distributed positive charge throughout the atom, like the cake in a plum pudding, and the electrons being detachable like the plums randomly scattered throughout the pudding.  This was put forward by JJ Thompson at the end of the 19th Century.

Nucleus - a concentration of mass and charge at the centre of the atom in the order of 10-15m.

Nuclear model of the atom - a model which explains the atom as having a nucleus and electrons orbiting around it.

Bohr model of the atom - a model which ascribes a certain fixed amount of energy to the electrons which keeps them in fixed energy levels around the nucleus.  (This is the start of the fascinating world of quantum Physics which we will revisit later in GCSE and again at A Level.)

Mass - a measure of the physical matter that an object has, it has units kilograms (kg).

Kinetic Theory - a model of matter that assumes all matter is made of particles that have more or less kinetic energy and have attractive forces between them of varying sizes.

Volume - a measure of the three dimensional space an object occupies, it has units metres cubed (m3)

Density - how much mass there is in a given volume, units kilogram per metre cubed (kg/m3)

Solid - a low energy state of matter, with atoms or molecules vibrating around fixed positions and held by strong attractive intermolecular forces.  Has fixed volume and shape.

Liquid - a medium energy state of matter with atoms or molecules which can change position held together by medium strength intermolecular forces.  It has a fixed volume, but it can change shape.

Gases - a state of matter with particles of a high kinetic energy, atoms or molecules have weak intermolecular forces and so can be spaced very far apart, moving in random directions.  It has no fixed volume or shape.

Fluid - a liquid or a gas, i.e. a substance which can flow.

Pressure - the force per unit area acting on a surface.  It has units Pascals (Pa) or Newtons per metre squared (N/m2).

Gas Pressure - pressure caused by particles of a gas colliding with a wall of a container.  It is equal to the sum of all the forces involved in collisions over one metre squared of the container.

Absolute zero - the lowest temperature theoretically possible. If a material was at absolute zero the atoms or molecules of it would have zero kinetic energy.  It is equal to -273°C, or 0K.

Boyle's Law - pressure and volume are inversely proportional (for a fixed mass of gas at a constant temperature), i.e. if you double pressure you half the volume.

Charles' Law - volume is proportional to temperature (for a fixed mass of gas at a constant pressure), i.e. if you double temperature you'll double the volume.

Gay-Lussac's Law - pressure is proportional to temperature (for a fixed mass of gas at a constant volume), i.e. double pressure

Atmospheric pressure - pressure caused by the weight of the gas in the atmosphere acting upon the surfaces below.  This will be lower at higher altitudes because there will be less weight of air acting on the surface.  At sea level it is 100kPa, which is equivalent to the relative unit 1atm.

Liquid pressure - pressure caused by the weight of the liquid acting upon the surfaces below it.  This is proportional to the depth submerged in the liquid and the density of the liquid.

Upthrust - upwards force on an object due to it's being submerged in a fluid.  Equal in size to the weight of displaced fluid.

Weight - the force due to gravity acting on a mass.     