Temperature is the thermodynamic magnitude that shows the thermal energy of one body in relation to that of another. This thermodynamic property describes only a macroscopic state.
According to molecular theory, temperature is defined as the measure of the average kinetic energy of the molecules that compose it. That is, the movements of the particles within it.
On the other hand, it can be defined according to statistical mechanics, as the derivative of energy in relation to entropy in constant volume.
Being of macroscopic magnitude, it has an exclusively statistical character. This means that it makes no sense to talk about the temperature of an isolated molecule or atom, but of the whole.
WHAT ARE THE TEMPERATURE SCALES?
The three most common scales for measuring temperature are:
- The Celsius scale . Measured in degrees centigrade.
- The Kelvin scale . Measured in Kelvin degrees (currently Kelvin )
- The Fahrenheit scale . Measured in degrees Fahrenheit .
SCALE CELSIUS AND KELVIN SCALE
The Celsius scale is the most used scale to express temperature. Almost everyone uses the Celsius scale ( degree Celsius ) to measure most measurements. The variation between one degree and the next on a Celsius scale is the same variation as on a Kelvin scale .
The difference between the Celsius and Kelvin scales is in fixing its null point:
- On the Celsius scale, 0ºC corresponds to the water freezing point.
- On the Kelvin scale, 0 degrees corresponds to the minimum level that a body could theoretically reach.
Kelvin scale intervals are measured in Kelvin, but were previously called Kelvin degrees .
However, there are some countries, mainly the United States, where the Fahrenheit scale is still used in everyday life. It is a historic scale. In it, the freezing point of water is 32 ° F and the boiling point of water is 212 ° F.
|description||Kelvin||Degrees Celsius||Degrees Fahrenheit||Rankine degrees|
|Absolute zero||0 0||-273.15||-459.67||0 0|
|Melting water temperature||273.15||0 0||+32||491.67|
|Boiling water temperature||373.15||100||+212||671.67|
|Human body temperature||310.15||37.||+98.6||558.27|
Ambient temperature is the temperature of the outside air. The maximum recorded was 56.7 degrees Celsius. Registered at Furnace Creek station, located in the well-known “Death Valley” of the USA. The recorded minimum is -93 degrees Celsius in Antarctica.
UNITY IN THE INTERNATIONAL SYSTEM OF MEASURES
The unit of measurement in the International System of Units (SI) is the kelvin. Kelvin is therefore the unit used by scientists. It is often seen as a Kelvin grade .
TRIPLE POINT OF WATER
The International System of Units (SI) defines a scale and unit for thermodynamic temperature based on the triple point of water.
WHY DO WE FEEL COLD AND HOT ?
Thermal sensation is called the sensation of cold or heat that a person feels according to a combination of meteorological parameters.
The physiological sensation is generated when there is an exchange of thermal energy between body temperature and that of other bodies.
If we touch an object at a lower temperature, heat flows from our body to the object. We feel cold. If the object is a good conductor of heat, the heat flows more quickly. Then we will have the thermal sensation that the object is even colder.
RELATIONSHIP BETWEEN TEMPERATURE AND THERMODYNAMICS
It is one of the main properties studied in a thermodynamic system . In thermodynamics , differences in thermals between different regions of matter are especially important. These differences allow the movement of heat from one region to another.
IS THE TEMPERATURE EQUAL TO THE THERMAL ENERGY?
The molecules of all material substances are always in continuous motion. They can be in vibration or agitation, due to the multiple interactions they suffer within the body.
As a consequence of this random agitation, the atoms and molecules of matter have a certain internal energy , since they have kinetic energy in the form of movement. They also have potential energy due to the forces exerted between the particles.
The internal energy is also known as the thermal energy of the bodies.
On the other hand, the temperature is the magnitude that allows to register the average value of the thermal energy of a body.
HOW IS THE TEMPERATURE MEASURED?
Different measurement systems depend on the application or whether very high or very low values are to be measured. However, the best known and most used tool is the thermometer.
To determine the temperature of a system, it must be in thermodynamic equilibrium. Variations in the thermal state of a body cause changes in some macroscopic properties:
- Evolution of electrical resistance.
- Creation of electromotive forces.
- Pressure changes.
- Volume changes in a gas, etc.
Consequently, variations in these properties allow them to be used in the construction of instruments that detect temperature variations.
Previously, the mercury thermometer was used to measure body temperature. It is currently out of use due to its danger.
WHAT DOES THIS MEAN IN THERMAL EQUILIBRIUM ?
When two systems are in thermal equilibrium , they have the same temperature. The extension of this principle fundamentally justifies the use of the thermometer and establishes the principles of its construction for its measurement.
In a more fundamental approach, the empirical definition is derived from the thermal equilibrium conditions, which are expressed in the zero principle of thermodynamics .