Capillary action means either of two things:
- When liquid moves through thin tubes.
- When liquid moves through something that is full of little holes (like a sponge).
Capillary action is a result of the surface tension of liquids.
An example of capillary action is what happens inside a drinking straw left in a cup of water. The force of adhesion which holds the water together and to the straw is a little stronger than gravity, so the water will rise inside the straw a little higher than the rest of the water.
Another example is what happens when putting a sponge in a puddle of water. The little bubbles in the sponge work like many straws gathered together. When the sponge is dipped in water, the water starts to go into the holes, and the bubbles that are inside the sponge pull on the water that they touch.