14 & 15 Particle Model & Forces and Matter

Absolute Zero

The lowest possible temperature. At this temperature the particles have no kinetic energy and so are completely stationary.w

Change in Thermal Energy

The product of mass, specific heat capacity and temperature change of a substance.

Chemical Changes

Changes to the chemical structure of a substance. The substance does not usually restore its original properties when the changes are reversed.

Condensation

The changing from vapour state to a liquid state, when a substance is cooled.

Density

The mass per unit volume of an object.

Evaporation

The changing from liquid state to a vapour state, when a substance is heated.

Freezing

The changing from a liquid state to a solid state, when a substance is cooled.

Gas Temperature

The temperature of a gas is directly proportional to the average kinetic energy of its molecules.

Gas

A state of matter in which the particles are spread apart to have a high kinetic energies. Any intermolecular forces acting between the particles are very weak.

Internal Energy

The energy stored stored by the atoms and molecules that make up a system. It is equal to the sum of the total kinetic and potential energies of the particles in the system.

Kelvin

The SI unit of temperature, based on an absolute temperature scale. To convert from degrees Celsius to degrees Kelvin, subtract 273 degrees.

Latent Heat

The energy required for a substance to change state.

Liquid

A state of matter in which the particles are in contact, but can flow over each other. Intermolecular forces act between the particles.

Melting

The changing from solid state to liquid state, when a substance is heated.

Pascals

The unit of pressure, equal to a force of one Newton acting perpendicular to an area of one metre squared.

Physical Chnages

Changes to the physical properties of a substance which can be reversed. Changes of state are physical changes since substances can restore their original properties when the changes are reversed.

Pressure of a Gas

The perpendicular force per unit area acting on the surfaces of a container as a result of the gas particles colliding with it.

Pressure

The force acting perpendicular to a surface, per unit area.

Solid

A state of matter in which the tightly packed together and can only vibrate about their fixed positions. Strong intermolecular forces act between the particles.

Specific Heat Capacity

The amount of energy needed to increase the temperature of one kilogram of a given substance by one degree Celsius.

Specific Latent Heat of Fusion

The amount of energy needed to change the state of one kilogram of a substance from solid state to liquid state, whilst held at constant temperature.

Specific Latent Heat of Vaporisation

The amount of energy needed to change the state of one kilogram of a substance from liquid state to vapour state, whilst held at constant temperature.

Specific Latent Heat

The amount of energy needed to change the state of one kilogram of a substance, whilst held at constant temperature.

Sublimation

The direct changing of a substance from a solid state to a vapour state, without passing through the liquid phase.

Temperature

A measure of the average kinetic energy of the particles in a substance. An increase in temperature will result in an increase in the particles’ kinetic energies and velocities.

Thermal Insulation

The addition of an insulating material to reduce the heat loss from a system.

Atmosphere

The thin layer of air surrounding the Earth, which gets less dense with increasing altitude. The pressure also decreases with increasing altitude.

Distortion

The changing of an object’s size or shape as a result of a deforming force.

Elastic Distortion

A non-permanent deformation for which the object will return to its original shape when the deforming forces are removed.

Elastic Limit

The force beyond which an object will no longer deform elastically, and will instead deform plastically.

Floating

An object will float if the volume of liquid it displaces has a greater weight than that of the object itself. The upthrust acting on the object is greater than its weight.

Fluid

A liquid or gas.

Hooke’s Law

The extension of a spring is directly proportional to the force applied to it, up to the limit of proportionality. The constant in this relationship is known as the spring constant.

Limit of Proportionality

The point beyond which the extension of an elastic object is no longer directly proportional to the force applied to it.

Linear Relationship

A relationship between two variables where if one variable increases, so does the other by the same factor. They produce straight lines when plotted.

Plastic Distortion

A permanent deformation for which the object will no longer return to its original shape when the deforming forces are removed.

Pressure in a Liquid Column

Equal to the product of the height of the column, the density of the liquid and gravitational field strength.

Sinking

An object will sink if the volume of liquid it displaces has a lower weight than that of the object itself. The upthrust acting on the object is lower than its weight and so there is a resultant downwards force.

Spring Constant

A measure of a spring’s stiffness. The higher the spring constant, the smaller the extension is for a give force.

Upthrust

The upward force acting on an object in a fluid, due to it experiencing a greater pressure below it than above it. It is equal to the weight of the fluid displaced by the object.

Weight

The force acting on an object due to gravity. It is equal to the product of the object’s mass and the gravitational filed strength at its location.