A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy (an explosive device). Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. One specific example is a nuclear weapon. This employs chemical-based explosives to initiate a much larger nuclear-based explosion. Bombs have been in use since the 11th century in Song Dynasty China.