The primary difference between fluid and liquid is that fluid is a general term for any substance that can flow, including both liquids and gases while, a liquid is a specific state of matter with a definite volume but no fixed shape, and is a subset of fluids.
What is Fluid?
A fluid is a substance that lacks a definite shape and easily deforms under external pressure. It includes both liquids and gases and is commonly used in applications like clutches and couplings to transmit power.
Definition of Fluid in Physics:
In physics, a fluid is defined as a substance that continuously deforms or flows when subjected to shear stress or external forces. Fluids, including liquids, gases, and plasmas, are characterized by their inability to resist shear forces, meaning they have zero shear modulus.
Everyday Examples of Fluids:
- A patient suffering from severe dehydration needs fluids urgently.
- Rooftop tanks store fluids such as oil, kerosene, and gas.
- Household cleaning fluids are kept out of children’s reach.
- The stomach produces gastric fluids to aid in digestion.
- We observed a viscous fluid oozing from the trunk of a tree.
What is Liquid?
Liquids are a state of matter characterized by the absence of a fixed structure and a defined volume. They take on the shape of the container they are placed in. Unlike gases, liquids have stronger intermolecular forces that keep their molecules close together, though not as tightly as in solids. This allows liquids to flow and adopt the shape of their container while maintaining a consistent volume.
The properties of liquids include:
- Fixed Volume: Liquids have a set volume but no fixed shape.
- Low Compressibility: Liquids are nearly incompressible.
- Molecular Proximity: Molecules in a liquid are relatively close to one another.
- Boiling Points: Liquids typically have boiling points above room temperature under standard conditions.
Fluid vs Liquid
The major difference between fluid and liquid is given below:
| Aspect | Fluid | Liquid |
|---|---|---|
| Definition | A state of matter that can flow due to pressure differences. | A state of matter that flows and takes the shape of its container. |
| Viscosity | Important for describing flow characteristics. | Affects flow; less viscous than solids, more than gases. |
| State | It can be both liquid and gas. | It specifically refers to the liquid state. |
| Compressibility | Can be either compressible or incompressible. | Incompressible. |
| Density | Varies based on compressibility. | Density remains relatively constant with pressure. |
| Volume and Shape | No fixed shape, conforms to container shape. | Fixed volume but no fixed shape; conforms to container. |
| Types | Includes both liquids and gases. | A subset of fluids. |
| Behavior under stress | possess deformation under applied stress. | possess viscosity and does not flow easily. |