“Vacuum” means the complete absence of matter. In order to create vacuum conditions, pressure within a given space must be lower than the surrounding environment. The quality of the vacuum is dependent upon several factors, including the number of particles within a given space. The inertia of moving particles exerts pressure, so fewer particles means lower pressure. Scientists have given up on the idea that a perfect vacuum is even possible; space is the most ideal vacuum we know of, but hydrogen atoms, energy waves and other moving particles are still present.
Imperfect as they are, we create vacuums for various applications and processes: sealed chambers that help researchers and manufacturers with tasks including leak testing, stress testing, degassing, drying, distillation, permeability testing, coating, specific gravity d