How do artillery shells know when to explode?

The do not know anything, but are detonated by one of a variety of devices. Old hollow cannon balls had a fuse, a burning wick permeated with gun powder. read more

The fuse would light, the “shell” cannon balls would fly and then explode at the estimated distance from the gun. Hopefully the gunner cut the fuse properly, and that the fuses all burned the same rate and the shell exploded over the enemy and not prematurely. read more

The explosive charge in an artillery shell is sufficiently stable that it won’t explode from the force of being fired, and generally won’t explode by itself from the force of impact either. It requires a fuze (trigger) that creates a small high-order explosion sufficient to explode the main charge. read more

There are several types of artillery shells. Some explode on impact, some explode after impact to allow penetration and some are time fuses so they can explode over a target. read more