Liquid vs Fluid
When you are sick and your doctor suggests you to take more fluids, what do you infer? Similarly when you buy brake oil to be used in your car and the container has brake fluid written over it, what do you make out of the term? This and other common usage of the term fluid are very confusing which is why people find it hard to differentiate between a fluid and a liquid. This article attempts to remove this confusion by high lighting the features of both of them and pointing out their differences.
A fluid is anything that flows. So naturally it includes both liquids and gases. A liquid is defined as a substance that occupies the shape of the container in which it is placed though keeping its volume. A gas on the other hand takes both the shape as well as the volume of the container. Thus it is clear that all liquids are fluids but not all fluids are liquids as fluids also contain substances in gaseous state.
All matter is either solid, liquid, or gas. But fluid is a subset of matter that includes liquids, gases, plasma, and even some plastic solids. However, the common usage of the term fluid creates an impression that it is a synonym for liquid and does not include gases. When plaster is being made by adding water to cement, it is in a fluid state but becomes a solid once it has been applied over a brick wall.
Liquid is one of the three phases of matter. It flows and takes the shape of the container in which it is placed. Surface tension is one of the most important characteristics of liquids which is responsible for the feeling of wetness when one touches a liquid with bare hands.
So, the difference between liquids and fluids boils down to their viscosity as fluids have a higher viscosity such as oils than liquids. Fluids can be gases also whereas liquids arte altogether different than gases.
What about dry sand, flour, baking soda, ground coffee beans, salt… these are all solids, yet they flow and fill a container because they are made of tiny grains or crystals. Could one say that they are fluid but not liquid?