What is the boundary between solid and liquid?

Question

Apparently a jar of peanut butter turned upside down will eventually settle on the bottom. (I just asked the question here: http://answers.yahoo.com/question/index;_ylt=AiBjbZA_AOrnS1uY_TYDupjsy6IX;_ylv=3?qid=20080806160734AAKoDfL).

Makes me wonder, how solid does a solid have to be, in order for it not to settle like peanut butter?

Sorry for the awkward phrasing, but I'm sure you can understand my question.

Answer 1

Glass (silicon dioxide) is a very very viscous liquid. Given enough time, all glass would settle like mush. But back to the question. Typical example of a solid is water ice. Aside from being able to sublime, that cube of ice will retain its shape and resist compression forever. That is the definition of a solid. Liquid water, aside from being able to evaporate, will have no shape but still resist compression forever. That is the definition of a liquid. To complete this picture, water vapor has no shape and can never resist compression. That defines a gas. Your example of peanut butter is a mixture of solids (mashed peanuts) and a liquid (oil). In other words, you have an emulsion that makes it a viscous liquid.

Answer 2

The glass answer is a misconception.

glass does not flow, the thick bottoms are usually from them setting the pieces that way (you wouldn't want to stick the thicker side at the top).

definition is that solids resist force and yes peanut butter is in-between as are most things since most thing will "flow" given enough pressure.

Added:

Again people, go to google, and type in "glass flow."

Answer 3

Glass will slowly flow, it takes centuries for a pane of glass to become noticeably thicker at the bottom. Does that make glass a liquid? No, it's classified as a solid.

So the border is a bit fuzzy, as so many things are in real life.

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