Dyson V7 Motorhead Cordless Vacuum – 5179374

The term cordless is generally used to refer to electrical or electronic devices that are powered by a battery or battery pack and can operate without a power cord or cable attached to an electrical outlet to provide mains power, allowing greater mobility. The term "cordless" should not be confused with the term "wireless", although it often is in common usage, possibly because some cordless devices (e.g., cordless telephones) are also wireless. The term "wireless" generally refers to devices that use some form of energy (e.g., radio waves, infrared, ultrasonic, etc.) to transfer information or commands over a distance without the use of communication wires, regardless of whether the device gets its power from a power cord or a battery. The term "portable" is an even more general term and, when referring to electrical and electronic devices, usually means devices which are totally self-contained (e.g., have built-in power supplies, have no base unit, etc.) and which may also use wireless technology.

Dyson may refer to:

• Dyson (surname), people with the surname Dyson
• Dyson (company), a Singaporean multinational home appliances company founded by James Dyson
• Dyson (crater), a crater on the Moon
• Dyson (operating system), a Unix general-purpose operating system derived from Debian using the illumos kernel, libc, and SMF init system
• Dyson sphere, a hypothetical megastructure that completely encompasses a star and captures most or all of its power output
• Dyson tree, a hypothetical plant suggested by physicist Freeman Dyson
  • Eufloria (formerly called Dyson), a video game based on the idea of Dyson trees
• USS Dyson (DD-572), a United States Navy destroyer in commission from 1942 to 1947
• NOAAS Oscar Dyson (R 224), an American fisheries and oceanographic research ship in commission in the National Oceanic and Atmospheric Administration since 2005
• Dysons, an Australian bus operator
• Dyson, a character in the Canadian television series Lost Girl
• The Charles H. Dyson School of Applied Economics and Management, often referred to as "Dyson"

A vacuum (pl.: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective vacuus (neuter vacuum) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum.

The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. But higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10⁻¹²) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm³. Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space.

Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Clemens Timpler (1605) philosophized about the experimental possibility of producing a vacuum in small tubes. 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 with mercury a tall glass container closed at one end, and then inverting it in a bowl to contain the mercury (see below).

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 development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.