Ballistic Pendula The first ballistic pendulum was invented in 1742 by Benjamin Robbins to measure the explosive energy of gunpowder. There are 2 pendula (or pendulums) on display, which were donated by the Health & Safety Establishment at Buxton, where they were used for testing mining explosives. They were erected at the Royal Gunpowder Mills in May 2007. The Ballistic Pendula Exhibition is located across from the Mad Lab. The Ballistic Pendulum This large pendulum uses a prototype mortar of 5 tons, which was made in 1856, probably for naval use. The actual pendulum is modern. How It Works The barrel, which has a 45mm bore and is mounted on rails, has a known weight of charge of propellant or explosive inserted into it. The barrel is then sealed with clay and rolled forward until it is 2 inches from the muzzle of the mortar. The charge is fired by an electrical detonator from a remote location and the amount of swing on the mortar pendulum is measured and by calculation gives the power of the charge. As the charge fires, the barrel recoils backwards on its track, away from the swinging mortar, ready for the next test. The Ballistic Mortar The age of this small mortar is not known, but it seems likely that it was made especially for the pendulum, which is modern. How It Works The mortar is filled with a known weight of propellant/explosive charge, and a steel plug of known weight is inserted into the barrel of the mortar. The mortar is fired using an electrical detonator, set off remotely, shooting the steel plug into a bank of sand. The mortar recoils, pushing a pointer up the curved scale, which can then be read off to give the power of the fired charge.