The hairy force.
One of the fundamental forces of biology, found in trees and other plants. Not usually associated with backpacking, but it does explain how all those trees got out there, and how they keep going.
A very smart person described capillary action as the "phenomenon of a liquid such as water spontaneously creeping up thin tubes and fibers", and that's pretty good. Trees especially are chock full of hairlike little tubes, and water, as you may or may not have guessed, likes to creep around inside those tubes where it's always dark and quiet and you can't see what's happening.
This is how water, as things go a not especially intelligent molecule, climbs from deep in the ground way up high, 300 feet (100 m) or more in the air, inside giant redwood trees, in one unbroken column of molecules. You can think of water as having tiny little hands all over itself, hands that grab onto the cell walls inside the capillaries, and onto other water molecules, though it's not teensy fingers that do the work but van der Waals forces.
They are the natural forces that attract water molecules to other water molecules and to many other things, something like a secret handshake discovered by a Dutch physicist named Johannes Diderik van der Waals. So now you also know what physics is good for.
When one water molecule at the top of a tree evaporates and flies away into the sunny sky on its tiny wings, it pulls the next water molecule behind it up one step, and that one pulls the one behind it and so on, and you can get dizzy thinking about it. This gets water and nutrients to the top of even the highest tree. If you were tall enough and had a really small ear you could bend over and place it at the top of a tree and listen to the water molecules pop loose one after another and go whizzing off into space, each emitting its own tiny squeak of joy.
So what is the connection to backpacking then?
Well, aside from providing us all with nice forests full of trees to hike around in, and some grassy meadows, capillary action is what gets us out of bed in the morning. Pay attention sometime and you'll learn how it works. You'll be lying there half conscious inside your sleeping bag. Then one eye will pop open all by itself and whether or not you want to you'll see that the day is bright and sunny and warm, a great day for continuing your backpacking trip.
Then before you know it the force of sunlight working on the top of your head will just sort of suck you right out of your tubular sleeping bag and there you'll be before you know how it even happened, standing upright, awake, and ready to go.
All hairy and gross around the edges maybe.
Possibly stinky, with a few desperate eye boogers hanging on, but pretty much ready to go.
And that's how capillary action relates to backpacking. It is nature's alarm clock.
So, as long as you're up, why not have a bath while there's still time?
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See if that helps.