Capillary number

Capillary number is like a measure of how much a liquid moves when there are tiny, narrow spaces for it to go through. Imagine you have a bunch of little straws all stuck together, and you pour water into one end. The water might not go through the straws very quickly because the straws are so small and narrow. But if you pour oil into the straws, it might move more easily because oil is thinner than water.

Capillary number is like a way to figure out how fast or slow a liquid will move through those little spaces. Scientists use a special formula to calculate capillary number based on things like the thickness and stickiness of the liquid, and the size of the tiny spaces it needs to move through.

So basically, capillary number helps people who study liquids figure out how easily those liquids can move through tiny spaces or pores. And when they know that, they can learn more about how liquids behave in different situations.