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
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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.
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.
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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.
Ummm, should one of us call the police?
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