Capillary action is when a liquid climbs up a narrow tube without external force. Only some liquids and some solids do this, and others do the opposite. This might seem like perpetual motion, but it does take energy away from the liquid.

In capillary action, the liquid gets attracted to the solid tube, and since the tube is very thin, the all of the liquid in the tube gets visibly higher. The reason the liquid gets attracted to the tube is because it reduces the chemical potential of the liquid (in the case of water and glass), which is usually favorable even in other physics like a ball on a hill (in this case, the potential is gravitational potential energy).

In capillary repulsion, basically the same thing happens, but the liquid dislikes the solid tube.

One example of capillary action is water and glass, which stick together since they are both polar.

An example of capillary repulsion is mercury and glass, which repulse each other because glass is polar and mercury isn’t.

diagram of capillary action Non-scientific diagram of capillary action