# What are compressible gases

## Difference between compressible and incompressible liquids

### Key difference - compressible vs. incompressible fluids

Liquids are a subcategory of matter that includes gases and liquids. Gases and liquids are referred to as fluids due to their flowability, deformability when force is applied and high flowability. At the atomic level, liquids are made up of atoms or molecules that flow easily; They are not tightly packed, and liquid takes the shape of the container it occupies. The main difference between compressible and incompressible fluid is that A force applied to a compressible fluid changes the density of a fluid whereas A force applied to an incompressible fluid does not significantly change the density. Although almost all liquids are compressible, liquids are called incompressible fluids and gases are called compressible fluids.

### Important areas

1. What is compressible liquid?
- definition, properties
2. What is incompressible fluid?
Definition, properties
3. What is the difference between compressible and incompressible liquids?
- Comparison of the main differences

Key Terms: Liquid, Compressible Liquid, Incompressible Liquid, Liquid, Gas, Density, Mach Number ### What is compressible liquid?

In general, gases (and plasma = ionized gas) are called compressible liquids. Under normal temperature and pressure conditions, the volume or density of a liquid does not change. However, gases show a variation in volume (hence density), even if there are only slight fluctuations in temperature or pressure. To name a particular compressible fluid, it should show a significant change in density when a pressure or force is applied.

In the advanced area of ​​fluid dynamic properties, the ratio between the flow velocity and the speed of sound in the liquid for compressible liquids is greater than 0.3. This ratio is also called Do number.

At the molecular level, pressure on a gas affects the gas in all directions, which means that the gas molecules lead to a high degree of collisions. These collisions give the gas molecules more time to interact with each other, and there can be more attractive forces between the molecules. These forces of attraction reduce the movement of gas molecules. This leads to the compression of the gas. Figure 2: Gas molecules in a container

### What is Incompressible Fluid?

Liquids are known as incompressible liquids. The volume or density of liquids is not easily changed when pressure is applied to them. According to fluid dynamics, the ratio between the flow velocity and the speed of sound in the medium should be less than 0.3 so that a fluid is incompressible. Therefore, this ratio for liquids is less than 0.3, making it an incompressible liquid.

In contrast to gases, the molecules or atoms in liquids are more densely packed (not as densely as in solids). Pressure exerted on the liquid therefore does not change the density significantly. In other words, the volume of the liquid is not reduced with a pressure exerted on the liquid.

Although fluids are considered incompressible due to fluid dynamics, fluids are compressible even when pressurized, but the change in density or volume is too small to be calculated. Hence, it is considered an incompressible liquid. Illustration of liquid molecules in a container

### definition

Compressible liquid: Compressible liquid is a matter that can be compressed using external pressure.

Incompressible liquid:Incompressible fluid is a matter that cannot be compressed using external pressure.

### volume

Compressible liquid:The volume of the compressible fluid can be reduced by applying pressure to the fluid.

Incompressible liquid:The volume of the incompressible fluid cannot be reduced by applying pressure to the fluid.

### density

Compressible liquid:The density of the compressible fluid can be changed by applying pressure to the fluid.

Incompressible liquid: The density of the incompressible fluid cannot be changed when pressure is applied to the fluid.

### Mach number

Compressible liquid:The value of Do number should be greater than 0.3 for a compressible liquid.

Compressible liquid:The value of Do number should be less than 0.3 for an incompressible fluid.

### Conclusion

A liquid is a substance that can flow easily. A liquid has no particular shape and takes the shape of the container in which it is located. There are very weak forces of attraction between the molecules of the liquid. Gas and liquid phases are considered liquids mainly because of their fluidity. Gases are called compressible liquids, while liquids are called incompressible liquids. The main difference between compressible and incompressible fluids is that a force applied to a compressible fluid changes the density of a fluid, while a force applied to an incompressible fluid does not change the density significantly.

##### References:

1. Chang, Raymond, and Kenneth A. Goldsby. Chemistry. New York: McGraw-Hill, 2016. Print.
2. "Compressible liquid". The free dictionary. Farlex, n.D. Netz.