There are many things around us that are so taken for granted that it never occurs to us to give them a second thought until we look a little closer. Coffee stains are one such thing. When coffee dries it leaves stains that are dark at the edges and lighter inside. The explanation may not be obvious...
Not a very good explanation. They take for granted that liquid will rush to fill the areas of the drop where evaporation is happening faster rather than the drop just shrinking in size. This really should have been part of the explanation, too.
Not a very good explanation. They take for granted that liquid will rush to fill the areas of the drop where evaporation is happening faster rather than the drop just shrinking in size. This really should have been part of the explanation, too.