How Will You Define Vacuum?
Vacuum is a completely empty space. In a vacuum pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal).
An “empty” room still contains air. Even the “empty” space between stars contains tiny amounts of gas. A perfect vacuum does not exist, but near-vacuums can be made. A vacuum can be created by removing air from a space using a vacuum pump or by reducing the pressure using a fast flow of fluid, as in Bernoulli’s principle.
As much as possible of the air is pumped out of a container, which is then sealed. Containers surrounded by a near-vacuum layer are used to keep food and other things warm or cool. They are called vacuum flasks.
Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, and then inverting it in a bowl to contain the mercury.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technologies has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.