Thermodynamics: The Physics of Heat
HEAT – Summary Notes
Things we think we know and can reasonably assume about the nature of heat:
- Heat MOVES
- Heat will move, from areas of high temperature to areas of lower temperature
- A consequence of #2 means all objects that are in contact will tend towards the same temperature if the system is isolated and there is no exchange of heat with the ‘outside’.
- Every individual material has some amount of heat, even an ice cube.
- Every individual material has a different rate at which it can change its temperature.
- Objects that can change their temperature quickly are said to have a high heat conductivity or thermal conductivity, and are called CONDUCTORS of heat.
- Objects that can not change their temperature quickly are said to have a low heat conductivity or thermal conductivity, and are called INSULATORS of heat.
- Objects can respond to an increase in heat by: (this is not a complete list, can you think of more?)
- Rising in temperature
- Our sensation of warmth:
- Is partly based on how quickly the object we are touching takes our heat or gives us heat, i.e. its thermal conductivity.
- Is partly based on how quickly our hand takes heat or gives heat as well.
- Is partly based on the relative difference in temperature between our hand (or skin) and the object we are sensing, i.e. the difference in initial temperature between our hand and the object. If we are warmer than the object, the object will feel cool and vice versa.
- A consequence of this is that our sensation of warmth is highly dependent upon RELATIONS between things inside us and things outside us. The state of the sensing organ when it senses is just as important as the thing it is sensing!
- Does not give us an absolute report of the temperature of an object according to a thermometer, because our sensation of warmth is not solely a sensation of temperature! (See note i. above)
- A thermometer really responds to warmth just like our hands do: it undergoes an internal change in time, based upon:
- the relative conductivities of itself and the object it is measuring
- the initial difference between the thermometer itself and the object