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Water in three states: liquid, solid (ice), and gas (invisible water vapor in the air). Clouds are accumulations of water droplets, condensed from vapor-saturated air. Video demonstrating states of water present in domestic life. Water is a chemical compound with the chemical formula H 2O. A water molecule contains one oxygen and two hydrogen atoms that are connected by covalent bonds. Water is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its solid state, ice, and gaseous state, steam (water vapor). Safe drinking water is essential to humans and other lifeforms even though it provides no calories or organic nutrients. Chemical and physical properties Impact from a water drop causes an upward "rebound" jet surrounded by circular capillary waves. Water is the chemical substance with chemical formula H 2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. The major chemical and physical properties of water are: Related:  Common connotations of BLUE

Ice A glacier is made from ice, itself resulting from snow accumulation. Frozen water in the form of an ordinary (household) ice cube. The white zone in the center is due to tiny air bubbles. Ice is water frozen into a solid state. Ice is used for a wide range of applications including cooling, winter sports and the art of ice sculpting. The word is derived from Old English īs, which in turn stems from Proto-Germanic isaz. Characteristics Crystal structure of hexagonal ice. As a naturally-occurring crystalline inorganic solid with an ordered structure, ice is considered a mineral.[2] It possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H-O-H. The result of this process is that ice (in its most common form) floats on liquid water, which is an important feature in Earth's biosphere. When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C. Hail

Fire The ignition and extinguishing of a pile of wood shavings Slow motion fire sequence 1000 frame/s The fire maps show the locations of actively burning fires around the world on a monthly basis, based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Fire in its most common form can result in conflagration, which has the potential to cause physical damage through burning. Physical properties Chemistry Fires start when a flammable and/or a combustible material, in combination with a sufficient quantity of an oxidizer such as oxygen gas or another oxygen-rich compound (though non-oxygen oxidizers exist that can replace oxygen), is exposed to a source of heat or ambient temperature above the flash point for the fuel/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a chain reaction. Fire can be extinguished by removing any one of the elements of the fire tetrahedron. Flame The glow of a flame is complex. Heat

Sky The sky (or celestial dome) is everything that lies a certain distance[clarification needed] above the surface of the Earth, including the atmosphere and outer space. In the field of astronomy, the sky is also called the celestial sphere. This is an imaginary dome where the sun, stars, planets, and the moon are seen to be traveling. During the day A greater proportion of blue light scattered by the atmosphere relative to red light. Civil, nautical, and astronomical twilight. Dawn is the beginning of morning twilight. Except for light that comes directly from the sun, most of the light in the day sky is caused by scattering, which is dominated by a small-particle limit called Rayleigh Scattering. Scattering also occurs even more strongly in clouds. The sun is not the only object that may appear less blue in atmosphere. Sky luminance distribution models have been recommended by the International Commission on Illumination (CIE) for the design of daylighting schemes. Dusk and dawn

Air (disambiguation) Air is the name given to the Earth's atmosphere. Air may also refer to: Donna Air, British actressGlen Air (born 1978), Australian rugby league player Sadness A detail of the 1672 sculpture Entombment of Christ, showing Mary Magdalene crying. In childhood[edit] Sadness is a common experience in childhood. Acknowledging such emotions can make it easier for families to address more serious emotional problems,[3] although some families may have a (conscious or unconscious) rule that sadness is "not allowed".[4] Robin Skynner has suggested that this may cause problems when "screened-off emotion isn't available to us when we need it... the loss of sadness makes us a bit manic".[5] Sadness is part of the normal process of the child separating from an early symbiosis with the mother and becoming more independent. Every time a child separates just a tiny bit more, he or she will have to cope with a small loss. Neuroanatomy[edit] Coping mechanisms[edit] A sad adolescent When some individuals feel sad, they may exclude themselves, in doing so they take time to recover from this feeling. Pupil empathy[edit] Pupil size may be an indicator of sadness.

Land Map showing Earth's land areas, in shades of green and yellow. Land rising from the sea. Land, sometimes referred to as dry land, is the solid surface of the Earth that is not permanently covered by water.[1] The division between land and water is one of the most fundamental separations on the planet. Land can also have a strong cultural value, as the vast majority of human activity occurs in land areas that support agriculture, habitat, and various natural resources Some life forms (including terrestrial plants and terrestrial animals) have developed from predecessor species that lived in bodies of water from specialized to exist on land. The demarcation between land and water varies by local jurisdiction. Etymology and terminology[edit] A contiguous area of land surrounded by ocean is called a landmass. A country or region may be referred to as the motherland, fatherland, or homeland of its people. History of land on Earth[edit] Artist's impression of the birth of the Solar System

Winter Winter (/ˈwɪntər/) is the coldest season of the year in temperate climates, between autumn and spring. It is caused by the axis of the Earth in the respective hemisphere being oriented away from the Sun. Different cultures define different dates as the start of winter, and some use a definition based on weather, but when it is winter in the Northern Hemisphere it is summer in the Southern Hemisphere, and vice versa. In many regions, winter is associated with snow and freezing temperatures. Cause[edit] The tilt of the Earth's axis relative to its orbital plane plays a big role in the weather. During winter in either hemisphere, the lower altitude of the Sun causes the sunlight to hit that hemisphere at an oblique angle. Meteorological reckoning[edit] Animation of snow cover changing with the seasons Accumulations of snow and ice are commonly associated with winter in the Northern Hemisphere, due to the large land masses there. Astronomical and other calendar-based reckoning[edit]

Aether Aether, æther or ether may refer to: Metaphysics and mythology[edit] Science and engineering[edit] aether theories in alchemy, natural philosophy, and very early modern physics that suppose a "fifth element" luminiferous aether, in early physics considered to be the medium through which light propagatesether, a class of chemical compounds, or specifically: diethyl ether, which has the common name "ether" Games[edit] Music[edit] Artists[edit] Albums[edit] Songs[edit] Other[edit] See also[edit] Ethernet, a computer communications technology

Police A police force is a constituted body of persons empowered by the state to enforce the law, protect property, and limit civil disorder.[1] Their powers include the legitimized use of force. The term is most commonly associated with police services of a state that are authorized to exercise the police power of that state within a defined legal or territorial area of responsibility. Police forces are often defined as being separate from military or other organizations involved in the defense of the state against foreign aggressors; however, gendarmerie are military units charged with civil policing. As police are often interacting with individuals, slang terms are numerous. Many slang terms for police officers are decades or centuries old with lost etymology. Etymology History Ancient policing In Ancient Greece, publicly owned slaves were used by magistrates as police. In the Roman Empire, the Army, rather than a dedicated police organization, provided security. Medieval policing

Pearl The most valuable pearls occur spontaneously in the wild, but they are extremely rare. These wild pearls are referred to as natural pearls. Cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those that are currently sold. Imitation pearls are also widely sold in inexpensive jewelry, but the quality of their iridescence is usually very poor, and often, artificial pearls are easily distinguished from genuine pearls. Pearls have been harvested and cultivated primarily for use in jewelry, but in the past they were also stitched onto lavish clothing. Pearls have also been crushed and used in cosmetics, medicines, and in paint formulations. Whether wild or cultured, gem quality pearls are almost always nacreous and iridescent, as is the interior of the shell that produces them. Etymology[edit] A pearl being extracted from an akoya pearl oyster. A black pearl and a shell of the black-lipped pearl oyster. Definition[edit] Physical properties[edit]

Royal family A royal family is the immediate family of a king or queen regnant, and sometimes his or her extended family. The term imperial family appropriately describes the family of an emperor or empress, while the terms ducal family, grand ducal family or princely family are more appropriate to describe the relatives of a reigning duke, grand duke, or prince. However, in common parlance members of any family which reigns by hereditary right are often referred to as royalty or "royals". It is also customary in some circles to refer to the extended relations of a deposed monarch and his or her descendants as a royal family. A dynasty is sometimes referred to as "the House of ...". As of July 2013, there are 26 active sovereign monarchies in the world – kings, queens, sultans, emperors, emirs and others – who rule or reign over 43 countries in all.[1] Members of a royal family[edit] The Royal Family of France in classical costume during the reign of Louis XIV. Current royal families[edit]

Star For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. Once the hydrogen in the core of a star is nearly exhausted, almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime and, for some stars, by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Binary and multi-star systems consist of two or more stars that are gravitationally bound, and generally move around each other in stable orbits. Observation history Historically, stars have been important to civilizations throughout the world.

Boy A boy is a young male human, usually child or adolescent. When he becomes an adult he's described as a man. The most apparent thing that differentiates a boy from a girl is that a boy typically has a penis while girls have a vagina. However, some intersex children with ambiguous genitals, and genetically female transgender children, may also be classified or self-identify as a boy. The term "boy" is primarily used to indicate biological sex distinctions, cultural gender role distinctions or both. The latter most commonly applies to adult men, either considered in some way immature or inferior, in a position associated with aspects of boyhood, or even without such boyish connotation as age-indiscriminate synonym. Etymology The word "boy" comes from Middle English boi, boye ("boy, servant"), related to other Germanic words for boy, namely East Frisian boi ("boy, young man") and West Frisian boai ("boy"). Characteristics of boys Uses of the term "boy" and related terms Military