Chapter

Similar topics in Freebase

• 

  Asteroid

  Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are smaller than planets but larger than meteoroids. The term "asteroid" has historically been applied primarily to minor planets of the inner...
• 

  Country

  In geography, a country is a geographical region. The term is often applied to a political division or the territory of a state, or to a smaller, or former, political division of a geographical region. Usually, but not always, a country coincides with a sovereign territory and is associated with a...
• 

  Continent

  A continent is one of several large landmasses on Earth. They are generally identified by convention rather than any strict criterion, with seven regions commonly regarded as continents – they are (from largest in size to smallest): Asia, Africa, North America, South America, Antarctica, Europe,...
• 

  City

  A city is a relatively large and permanent settlement, particularly a large urban settlement. Although there is no agreement on technical definitions distinguishing a city from a town within general English language meanings, many cities have a particular administrative, legal, or historical status...
• 

  Electric current

  Electric current can mean, depending on the context, a flow of electric charge (a phenomenon) or the rate of flow of electric charge (a quantity). The electric charge that flows is carried by, for example, mobile electrons in a conductor, ions in an electrolyte or both in a plasma. The SI unit for...
• 

  Calendar date

  A date in a calendar is a reference to a particular day represented within a calendar system. The calendar date allows the specific day to be identified. The number of days between two dates may be calculated. For example, "24 October 2009" is ten days after "14 October 2009" in the Gregorian...
• 

  Density

  The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho). Mathematically: where: Different materials usually have different densities, so density is an important concept regarding buoyancy, metal purity and packaging. In some cases density...
• 

  Electromagnetic radiation

  Electromagnetic radiation (often abbreviated E-M radiation or EMR) is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the...
• 

  Electromagnetic field

  The electromagnetic field is a physical field produced by electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. Light is the electromagnetic field in a certain frequency range. At lower frequencies the electromagnetic field may be radio waves or...
• 

  Electric charge

  Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source...