Temperature Is a property of an object which determines the direction of net heat flow when an object is placed in contact with some other object. Heat is a form of energy while temperature gives an indication of “hotness” or “coldness”

On a molecular level the temperature of a body is a measure of the average kinetic energies of the molecules of the body

A change in temperature can cause certain physical properties of substances to vary: Volume of a liquid or gas E.m.f. between the ends of two different wires joined Electrical resistance of a metal The pressure of a constant volume of gas

Instruments used to measure temperature change: Thermometers: Laboratory thermometers: mercury in glass, alcohol in glass Clinical thermometers Thermocouples

The centigrade scale/the Celsius scale In order to express temperatures a scale and a unit of temperature was used and defined temperatures of: - 0°C lower fixed limit and 100°C upper fixed limit (the 100 equal parts is the fundamental interval)

The Kelvin For measurements and calculations in Science we convert °C to Kelvin: + 273 to the °C value

Theories of heat Caloric theory: -heat was considered to be an invisible fluid called caloric -temperature changes in a body was due to the addition or removal of caloric -temperature was directly dependant on the amount of caloric it contained - Supported by experiments involving mixture of 2 materials at different temperatures that become same temperature

Theories of heat Caloric theory failed in that -a material did not necessarily gain weight if it gained temperature 2 bodies supplied with the same amount of heat do not reach same temperature Addition of heat does not produce a temperature rise (melting, boiling) Friction generates heat…where was this coming from?

The kinetic theory seemed to have the answers: Rumford observed that heat was produced by friction in canon boring due to the work being done by horses which powered the boring machines The kinetic theory explains that the heat content of a body is the sum of the kinetic energy of the individual particles of matter contained in a body Heat is a form of energy measured in Joules (name given by scientist who proved using experiments)

NOT all materials provided with the same amount of heat energy for the same length of time has the same temperature rise, such as if wood is receives the same amount of heat energy that an equivalent piece of iron receives which do you think will show a higher rise in temperature? Different materials have different heat capacities Heat capacity and Specific Heat capacity are not the same Heat capacity is the amount of heat required to raise the temperature of a body (for a specific material) by 1K Specific heat capacity, c is defined as the quantity of heat which is needed to raise the temperature of 1 kg of a body by 1K or 1 °C Specific heat capacity includes the mass of the material

Three major methods of heat transfer in materials Conduction – mostly in solids Convection – mostly in fluids Radiation – mostly in a vacuum or gases

Convection By the variation of density of the material a convection current is set up such that the less dense fluid rises and the more dense fluid sinks to below

Radiation Transfer of heat energy via electromagnetic waves because the energy travels in a combination of electric and magnetic waves. This energy is released when these waves are absorbed by an object. For example, energy traveling from the sun to your skin, you can feel your skin getting warmer as energy is absorbed.