In summer, there is a lot of water vapor in the air. When water vapor meets cold popsicles, it liquefies to form small water droplets, that is, "white gas". Because white gas is small water droplets and its density is greater than that of air, the "white gas" emitted from popsicles moves downward.

At a certain temperature and pressure, the mass per unit volume of air is the air density. Under standard conditions (0℃, 1 standard atmospheric pressure (1atm)), the air density is about 1.29Kg/m? .

Extended data:

Variation law of density

Generally speaking, no matter what substance, no matter what state it is in, with the change of temperature and pressure, the volume or density will change accordingly. The relationship between temperature T, pressure P and density ρ (or volume) is called the equation of state. The volume of a gas varies significantly with the pressure it is subjected to and the temperature it is at. For an ideal gas, the equation of state is? Where r is a gas constant, equal to 287.14m2 (2* seconds).

If its temperature is constant, the density is proportional to the pressure; If its pressure is constant, its density is inversely proportional to its temperature. For general gas, if the density is not large and the temperature is far from the liquefaction point, its volume changes with pressure close to the ideal gas; For gas with high density, the above equation of state should also be corrected appropriately.

The density of a solid or liquid substance changes only slightly when the temperature and pressure change. For example, in the vicinity of 0℃, the temperature coefficients of various metals (the rate of change of object volume when the temperature rises 1℃) are mostly around 10-9. The pressure in deep water and underwater explosion can reach hundreds of atmospheres, or even higher (1 atmospheric pressure =101325pa), so the change of density with pressure must be considered.

R.H. Cole suggested the following equation of state: where p0 is the density of water at one atmospheric pressure. If n and b are taken as 7 and 3000 atmospheres, the error between the above formula and the measured data is in the range of several percent up to 105 atmospheres.

As far as the whole nature is concerned, extreme pressure will make the density of substances in some celestial bodies very different from the common density.

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