Some people may think that temperature and thermal conductivity are the same measurement, but they are not. Temperature is the measurement of the heat level of a particular material at a particular moment in time. This measurement is almost always in constant flux in any material. Thermal conductivity, on the other hand, is a universal property that quantifies the capability and tendency of a certain type of matter to transmit heat while at a specified temperature.
For instance, you can say that aluminum always has a thermal conductivity of 250 W/(mK) while holding a temperature of 25 degrees Celsius, but you cannot say that aluminum always has a temperature of 25 degrees Celsius.
The three most common ways of expressing temperature are by using the Fahrenheit (°F), Celsius (°C) and Kelvin (K) scales. Zero degrees Celsius is the temperature at which water freezes, while zero degrees Fahrenheit is the frigorific temperature that results from a mixture of ammonium chloride and ice. Zero degrees Kelvin lies at "absolute zero," the theoretical lowest possible temperature for all matter (−459.67°F or −273.15°C).
Physicists use many different representations to express thermal conductivity, but the most common representation is W/(mK). The "W" in this expression stands for "watts," a measurement for energy (or heat). The "m" stands for "meters," while the "K" stands for Kelvin. In order to calculate the thermal conductivity of a material, you must first multiply the heat of the sample with the distance through which the heat will be traveling. Divide this figure by the product of the surface area and the temperature gradient (difference in temperature).
In every field of science, temperature is a very fundamental measurement that can make huge differences. In chemistry, for instance, certain chemical reactions will not occur until the materials involved reach a certain temperature level. In physics, the temperature of a material will determine its state (solid, liquid, gas or plasma), and even within the bounds of a specific state, the temperature affects behaviors. For instance, matter generally contracts as it becomes colder and expands as it becomes hotter. When materials contract, they become harder and denser, and when they expand, the opposite occurs.
By showing their tendency to resist or absorb heat, the thermal conductivity of materials is an integral part of many engineering projects. For example, though most metals can handle high levels of heat without melting, they also conduct that heat very freely, such that less heat-resistant components that are nearby can receive damage. Engineers solve this problem by taking something with a low thermal conductivity level, such as a ceramic material, and placing it in between. Engineers must know the thermal conductivity of various materials in order to do this.
People use thermometers to measure temperature. There are two basic types of thermometers: solid- and liquid-based. Solid-based thermometers have a coil of two different types of metal put together. As temperatures change, the different thermal conductivity levels of the two metals cause the coil to ravel or unravel and move a dial. In liquid-based thermometers, a liquid such as alcohol or mercury expands or contracts within a tube that has temperature markings on it.
According to Calculator.org, the two main ways of calculating thermal conductivity are by using the steady-state method and the transient method. The steady-state method measures a material's conductivity at a given point once the entire sample is the same temperature, while the transient method uses multiple thermometer probes that track the rate of temperature change from the heat source.
Speculation in the measurement of heat and thermal conductivity deal mostly with absolute zero, as physicists have yet to witness a specimen of matter that actually exists at absolute zero. Some believe that nothing can exist below this temperature, while others say that matter simply passes into a different state of existence upon crossing this threshold.