how water can defy gravity

Question

I recently soaked my sons onesie overnight in water and oxiclean. The legs and feet were sticking out of the bowl onto the counter. The next morning most of the water had traveled up and out though the legs (this bowl was not short either, it was part
Of our salad spinner.)

In: 142

Answer 1

It happens due to osmotic pressure.

An object such as a rock on a hill has potential energy. Push the rock and it falls to the bottom of the hill, releasing that energy. Once at the bottom, the energy is exhausted. To get more energy out, you have to push the rock back up the hill.

Porous materials have a similar potential energy that creates osmotic pressure. When liquid is applied, this potential energy tries to make the two sides of the material balance, such that they have equal liquid on both sides. This potential energy pulls the liquid through the material in all directions, including up.

Once the liquid permeates the porous material, the potential energy is exhausted. To get more energy out, you have to replenish that potential energy. Evaporation adds energy, which dries out the material and restores that energy.

So long as there is energy to evaporate the liquid, this process can pull up more liquid indefinitely. This is what allows trees to pull water out of the ground and up to their leaves where it evaporates.

EDIT: As was pointed out in a reply, I have confused osmotic pressure with capillary action.

It is not osmotic pressure that causes this. Capillary action gets its energy from a tendency for dry materials to pull at water (adhesion), some more than others. This is why some surfaces get wet all over and some “bead up” and make separate droplets. The surfaces that bead up have low adhesion so the water’s tendency to clump together (cohesion) overrides adhesion and makes a shape closer to a sphere.

With capillary action, high adhesion combined with small tubes (effectively it focuses adhesion onto a smaller area) allows adhesion to overcome cohesion and gravity.

Other than that, what I said above applies. The adhesion contains potential energy that overcomes gravity but gets “used up” by becoming wet. Any additional tendency to rise is caused when evaporation dries out the material at the top, refilling the pool of potential energy.