Solid, in physics and chemistry, one of the three states of matter. The other two states of matter are gas and liquid. A solid tends to maintain its shape without a container. Some solids are harder than others. True solids are crystalline; that is, the atoms of which they are composed are arranged in definite, three-dimensional patterns. They have definite melting temperatures. Some substances, such as glass and tar, that appear to be solid are amorphous—they do not have a crystalline atomic structure. These substances soften and melt over a range of temperatures; they are not true solids.
About 90 percent of Americans consume some form of caffeine every day: It's our most popular drug by far. What's so special about this stimulant?
Most of us have heard the talk about oysters and chocolate, and maybe you've read an article about the stimulating effects of ginseng. But garlic, licorice and cucumber? Learn about the history of aphrodisiacs and whether they've been proven to be effective.