Many people have played with the incredibly fun, and apparently explainable solid/liquid substance known as oobleck. Oobleck is made up of starch in water, and exhibits an apparent change in states when it is hit by a fast moving object: it goes from liquid to solid. This can be explained by the startch which was added to the water. Starch is an extremely long chain of glucose. This length means that when a substance hits the substance quickly, the friction between the molecules becomes so great that it does not moving; creating a temporary solid.
However, length is only one possible reason for the exhibition of this trait. Intramolecular properties between compounds in calcium Carbonate (CaCO3) also make this happen. Some people are trying to use this property in the common compound by creating fluid armor, which would be flexible, and light, but would solidify as soon as it is impacted with a fast moving object, such as a knife or a bullet.
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