Quick Answer: An explosive is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material. The material may either be composed solely of one ingredient or be a mixture containing at least two substances. The potential energy stored in an explosive material may, for example, be: • chemical energy, such as nitroglycerin or grain dust • pressurized gas, such as a gas cylinder, aerosol can, or boiling liquid expanding vapor explosion • nuclear energy, such as in the fissile isotopes uranium-235 and plutonium-239__###newline###__ Explosive materials may be categorized by the speed at which they expand. Materials that detonate, in which the front of the chemical reaction moves through the material faster than the speed of sound, are called "high explosives."