The Clepsydra (pronounced “clep-see-drah”), more commonly referred to as the “water clock”, was among the earliest technological devices engineered for measuring time, predating mechanical clocks by over a millennia. The earliest known example of a clepsydra is from Ancient Egypt, constructed close to 1400 B.C., and attributed to an Egyptian court official named “Amenemhet” (pronounced “ah-men-ehm-het”). Clepsydra clocks operated using 1 of 2 primary designs; which includes both outflow and inflow setups. In an outflow clepsydra, water exited the chamber container through a small hole at the bottom, and the measurement of time was tracked by the continually lowered water level which was measured against internal markings. Inflow clepsydras reversed this design setup with water entering a marked container vessel, and the continually rising water level indicating the amount of time which had elapsed. The main challenge of the inflow and outflow designs was maintaining a consistent flow rate of water because as water drained, pressure dropped which slowed the drip rate and skewed the clocks accuracy. Ancient Greek engineer Ctesibius (pronounced “teh-sib-ee-us”) addressed this problem by introducing an overflow tank with a fixed water level, ensuring constant pressure and uniform water flow at all times. Ctesibius also added a float regulated valve system, an early feedback mechanism designed to stabilize inflow of water and prevent overflow, much the same as the float controlled fill valve (e.g. ballcock, float cup valve, diaphragm type inlet valve etc.) installed within toilets during the modern day. Subsequent future cepsydra designs implemented gears and escape mechanisms to convert water movement into mechanical energy/motion. Chinese engineers expanded further upon the concept of the clepsydra by introducing polyvascular systems, in which water flowed through multiple containment vessels in an effort to better regulate timing intervals. These innovations permitted water clocks to function independently of sunlight unlike sundials, the prevailing time keeping technology throughout history, and laid the foundation for regulated mechanical timekeeping which proceeded it. Despite limitations (e.g. temperature dependent viscosity, leakage and evaporation, the need for constant manual maintenance by human beings etc.), clepsydras remained in use for centuries and were the first controlled, replicable timekeeping systems in history only falling out of fashion during the late Middle Ages due to the ascendency of mechanical, pendulum and gear based clocks
During the modern day, soldiers use plastic explosives to blast through walls, similar to that of the gunpowder powered cannons of antiquity, but different in the sense that they can be directly applied and finely controlled. Despite these differences, the principle of both weaponry remains the same which is to create a powerful burst of kinetic energy to smash apart solid structures. Soldiers with explosive expertise during the modern day plant explosives in a lowercase “i” or “t” shape format by separating the explosives with a gap in the middle. This design ensures the explosive will blow a hole in the top and the bottom of the blast site, as well as the sides in some instances, leveraging the physics of the shockwaves produced to disrupt the wall and weaken it in the middle. Explosive experts don’t attach plastic explosives at the bottom of walls for two distinct reasons, the first being because the foundation upon the other side of the wall which cannot be viewed has the potential to be higher than the foundation facing the impending soldiers, which means that the explosives would be blasting into solid ground soil which is much less effective than blasting into walls made of concrete or otherwise, and the second being that explosives close to the ground create rubble directly next to the hole created, making forced entry more difficult, especially under siege conditions with active enemy combatants attempting to stop the breach. The main difference between Medieval gunpowder and modern day plastic explosive is the amount of material required to produce the same effect as plastic explosives are an entire order of magnitude more powerful than gunpowder, with 2 kilograms of plastic explosive equating to multiple barrels of gunpowder. Explosives are categorized as either “high explosives” or “low explosives” with high explosives having the front of the chemical reaction travel faster than the speed of sound and low explosives having the front of the chemical reaction produced travel slower than the speed of sound. To provide comparison, modern day C4 plastic explosives have a detonation velocity of 8,092 meters per second whilst gunpowder has a detonation velocity of just 171 – 631 meters per second