Query: “Temperature, like viscosity and density, and of course phone numbers, is not something that can be meaningfully averaged. ‘

Relevant passages:
Density <=SEP=> The density , or more precisely , the volumetric mass density , of a substance is its mass per unit volume . The symbol most often used for density is ρ ( the lower case Greek letter rho ) , although the Latin letter D can also be used . Mathematically , density is defined as mass divided by volume :   where ρ is the density , m is the mass , and V is the volume . In some cases ( for instance , in the United States oil and gas industry ) , density is loosely defined as its weight per unit volume , although this is scientifically inaccurate -- this quantity is more specifically called specific weight .   For a pure substance the density has the same numerical value as its mass concentration .  Different materials usually have different densities , and density may be relevant to buoyancy , purity and packaging . Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser .   To simplify comparisons of density across different systems of units , it is sometimes replaced by the dimensionless quantity `` relative density '' or `` specific gravity '' , i.e. the ratio of the density of the material to that of a standard material , usually water . Thus a relative density less than one means that the substance floats in water .   The density of a material varies with temperature and pressure . This variation is typically small for solids and liquids but much greater for gases . Increasing the pressure on an object decreases the volume of the object and thus increases its density . Increasing the temperature of a substance ( with a few exceptions ) decreases its density by increasing its volume . In most materials , heating the bottom of a fluid results in convection of the heat from the bottom to the top , due to the decrease in the density of the heated fluid . This causes it to rise relative to more dense unheated material .   The reciprocal of the density of a substance is occasionally called its specific volume , a term sometimes used in thermodynamics . Density is an intensive property in that increasing the amount of a substance does not increase its density ; rather it increases its mass .

Viscosity <=SEP=> The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress . For liquids , it corresponds to the informal concept of `` thickness '' ; for example , honey has a much higher viscosity than water .   Viscosity is a property of the fluid which opposes the relative motion between the two surfaces of the fluid in a fluid that are moving at different velocities . When the fluid is forced through a tube , the particles which compose the fluid generally move more quickly near the tube 's axis and more slowly near its walls ; therefore some stress ( such as a pressure difference between the two ends of the tube ) is needed to overcome the friction between particle layers to keep the fluid moving . For a given velocity pattern , the stress required is proportional to the fluid 's viscosity .   A fluid that has no resistance to shear stress is known as an ideal or inviscid fluid . Zero viscosity is observed only at very low temperatures in superfluids . Otherwise , all fluids have positive viscosity , and are technically said to be viscous or viscid . In common parlance , however , a liquid is said to be viscous if its viscosity is substantially greater than that of water , and may be described as mobile if the viscosity is noticeably less than water . A fluid with a relatively high viscosity , such as pitch , may appear to be a solid .

Population density <=SEP=> Population density ( in agriculture : standing stock and standing crop ) is a measurement of population per unit area or unit volume ; it is a quantity of type number density . It is frequently applied to living organisms , and most of the time to humans . It is a key geographical term .

Thermodynamic temperature <=SEP=> Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics .   Thermodynamic temperature is defined by the third law of thermodynamics in which the theoretically lowest temperature is the null or zero point . At this point , absolute zero , the particle constituents of matter have minimal motion and can become no colder . In the quantum-mechanical description , matter at absolute zero is in its ground state , which is its state of lowest energy . Thermodynamic temperature is often also called absolute temperature , for two reasons : one , proposed by Kelvin , that it does not depend on the properties of a particular material ; two that it refers to an absolute zero according to the properties of the ideal gas .   The International System of Units specifies a particular scale for thermodynamic temperature . It uses the kelvin scale for measurement and selects the triple point of water at 273.16 K as the fundamental fixing point . Other scales have been in use historically . The Rankine scale , using the degree Fahrenheit as its unit interval , is still in use as part of the English Engineering Units in the United States in some engineering fields . ITS-90 gives a practical means of estimating the thermodynamic temperature to a very high degree of accuracy .   Roughly , the temperature of a body at rest is a measure of the mean of the energy of the translational , vibrational and rotational motions of matter 's particle constituents , such as molecules , atoms , and subatomic particles . The full variety of these kinetic motions , along with potential energies of particles , and also occasionally certain other types of particle energy in equilibrium with these , make up the total internal energy of a substance . Internal energy is loosely called the heat energy or thermal energy in conditions when no work is done upon the substance by its surroundings , or by the substance upon the surroundings . Internal energy may be stored in a number of ways within a substance , each way constituting a `` degree of freedom '' . At equilibrium , each degree of freedom will have on average the same energy : where is the Boltzmann constant , unless that degree of freedom is in the quantum regime . The internal degrees of freedom ( rotation , vibration , etc. ) may be in the quantum regime at room temperature , but the translational degrees of freedom will be in the classical regime except at extremely low temperatures ( fractions of kelvins ) and it may be said that , for most situations , the thermodynamic temperature is specified by the average translational kinetic energy of the particles .