Why is it, when you try to wipe away drops of blood off of a surface, it leaves a behind a thin ring around it which is harder to clean?
In: Physics
Ummm, should one of us call the police?
I am no scientist but it makes sense that the edges would dry first. Even if the top of the middle of a blood drop dries out, the bottom of the middle would still be fluid. Hope that makes sense. & yes blood is sticky. Protein is sticky stuff.
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Because blood coagulates (changes from a liquid to solid as it dries). The outer edges of the blood dry first and stick to the surface. Other liquids that also do this are paints are milk.
I get this same effect when I spill coffee on the kitchen counter. If I don’t wipe it up immediately, when I do, a dark outline of the spill is left behind after the first swipe.
This suggests that the effect you asked about isn’t related to the specific composition of blood, but to fluids in general.
Jesus, how much blood do you have to clean up before you start to notice these things? With that being said, the outside of the blood puddle is coagulating from the oxygen, you leave it there long enough and the whole mess will harden.
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Blood when exposed to air tries to clot, the different components in the blood meant to close wounds bind together.
This happens faster at the edges.
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