How does absorption work? Why is it that rubbing yourself with a towel mostly dries you off, but rubbing yourself with a banana or a rock doesn’t?

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Sorry if I got the flair wrong, I actually don’t even know what kind of science is at play here!

In: Chemistry
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There’s two forces involved. There are *cohesive* forces that bond the water to itself, and there’s *adhesive* forces that can connect the water to some other thing. The relative strength of these forces is the important part. (These properties are determined by the materials you’re using)

When you have low amounts of adhesion, then the water stays together, and doesn’t absorb into the material. This is the banana or rock example.

When you have high adhesion, then it overcomes the cohesive force, and it combines with your towel.

Think absorption like transfering matter from one body to another. How much rubbing works depends on how much the “receving” material can absorb (in this case) water. This property is called [hydrophilia](https://en.wikipedia.org/wiki/Hydrophile).

More “porous” objects (like sponges) absorb more water than more “compact” things (like steel), since there’s more “space” for the water to come through. In addition, the material is also relevant, because some materials interact with water molecules more easily than others.

* Surface area.
* A towel has lots of tiny little fluffy threads and each one has some surface area and can absorb some water.
* A banana (as compared to a towel) is very smooth and so have a very small surface area to absorb water.

In addition to the other comments, there is a term called [capillary action](https://en.m.wikipedia.org/wiki/Capillary_action) which is the ability of a liquid to flow into narrow spaces without help from external forces such as gravity, or even against them. This is why water for instance, can climb up a napkin or paper towel.

Not every liquid works the same way. Mercury for instance, does not absorb into sponges. [These ](https://youtu.be/PWCx3faQSfQ) two [videos](https://youtu.be/X3g3ODDP9dU) by Taofledermaus take a hit of a look into why that is. As he mentions in one of the videos, and two of the other comments mentioned, it’s not because sponges have holes. Making bigger holes doesn’t mean the mercury is absorbed, it just sits inside the holes. Sponges work because they have LOTS of teeny tiny, LITTLE holes, surrounded by tons and tons of fibers. Water can cling to all the little fibers and gets pulled up through the capillary action I mentioned earlier. Relatively speaking, at least. The spaces themselves are pretty small overall, but are large in comparison to the surrounding fibers. The water does need somewhere to go after all.