What is Fluids?

Fluids are anything that can flow — this includes liquids like water and juice, and gases like air and steam. Unlike solids, fluids don’t have a fixed shape. They take the shape of whatever container they’re in. For example, water in a glass looks different than water in a bottle — it changes shape, but not its amount. Fluids can move, be poured, and even create pressure (like water pushing out of a hose or air filling a balloon). So, fluids are materials that can flow and move freely, and we use them all the time in daily life.

Fluids — which include liquids and gases — are one of the main states of matter, but studying how they flow and behave under pressure or temperature has helped scientists discover other, more unusual states of matter, like plasma and superfluids. For example, when gases are heated to extremely high temperatures, their atoms break apart and form plasma — a super-hot, glowing fluid found in stars and lightning. And when certain liquids are cooled to very low temperatures, they can become superfluids, which flow with zero resistance — they can even climb up walls or stay in motion forever without slowing down! So, while fluids are a basic form of matter, they open the door to understanding more advanced and exotic forms of matter in science.