Difference Between Fluid and Liquid

What is fluid? 

The fluid is a substance that can flow or deform continuously under the shear stress applied. A fluid is known as a type of matter that can flow from one place to another without any traits of rigidity. The shear stress condition is where the stress is parallel to the surface of the material. Consequently, the term fluid includes water and gas. It is a phase of matter that contains liquids, gases, plasma, and some types of plastic solids. The fluid lacks rigidity and cannot withstand shear force when applied to it. Even, shortly after that it flows and changes shape. There are intermolecular forces in the liquid that holds it together so that it has volume but no definite shape. 

There are, of course, differences between liquids and gases. Gasses are readily compact, while liquids are almost incompressible. The liquid has a certain duration, but the gas expands to fill every closed vessel holding it. However, when describing the mechanical behaviour of fluids, we only use the properties of liquids and gases connected with their ability to flow. The same fundamental laws, therefore, govern the static and dynamic behaviour of liquids and gases. Unlike solids, fluids can change shape quickly, so their mechanical behaviour cannot be defined as rigid body mechanics, as is the case for solids. 

What is liquid?

The liquid is a state of matter in which there is no defined structure and a fixed amount of matter. The shape of the jar in which it is placed is taken up by the liquid. In the case of the liquid, the particles have a strong intermolecular force on the gas particles. Owing to surface tension, the liquid always has a small surface area.

Liquids flow because intermolecular forces between molecules are weak enough to enable the molecules to travel relative to each other. The forces are intermolecular forces between the neighbouring molecules.

At the molecular level, liquids have certain gas and solid properties. Fluids are both liquid and gas, which means that the intermolecular forces cause the molecules to pass. The material does not have any fixed shape in the gas and liquid phase and instead retains the shape of the container in which it is contained.

Physical Properties of Liquid

  • Liquid volume is fixed but the shape is not shaped.

  • Liquids are almost incompressible.

  • Molecules are pretty close to each other in liquids.

  • The liquids have their boiling points, in normal conditions, above room temperature. 

The Difference Between the Fluid and the Liquid

The fluid is the state of a specific substance, while the liquid is one of the states of matter. The basic characteristic of fluids is the flow of fluids. You will need to mention its viscosity when describing a fluid material. Liquids, on the other hand, flow and are described as having volume with no fixed shape. 

All liquids are fluids but not all fluids are liquids. Fluids are described as something that can flow as a result of a pressure differential between two points. Liquids, on the other hand, are a subset of liquids. Liquids are incompressible liquids. There are fluids whose density does not change sharply with pressure.

Gasses are also fluids, which form compressible fluids. They do flow as a result of the difference in friction between two points, but at the same time, they can be compressed or extended. Their density is fluctuating with the pressure.

As a consequence, fluids consist of 2 mutually exclusive classes of compressible and incompressible fluids. Liquids are incompressible fluids and thus constitute a subset of the more general word fluid.





A form of matter that can flow from one place to another through any opening without showing any traits of rigidity.

A phase of matter which depends on the prevailing temperature and pressure of a particular substance.


It may or may not have some level of viscosity

It has volume but no shape

Reference to gas and liquid


No gas, only liquids


Water, honey, air, mercury, gasoline, etc.

Water, blood, milk, wine, coffee, etc.

Fun Facts

  • Gas pressure is measured in pascals.

  • During the process of becoming a butterfly, the entire caterpillar will break down into a liquid.

FAQs (Frequently Asked Questions)

1. Why is Liquid Incompressible?

Liquids are commonly referred to as incompressible. The molecules are so close together so they can hardly be pressed any further. Liquids can potentially compress under extremely high pressures, but not too much. Unlike oils, liquids have a clear surface that they do not need to assume the shape of their container.

2. Is Water a Liquid or Fluid?

Water is by far the most common material on Earth. Water density is usually comparable to that of a solid, which is far higher than that of a gas. Both liquid and solid are also known to be condensed matter. On the other hand, they are called fluids since liquids and gases can flow.