The absorption, emission, or scattering of electromagnetic radiation by atoms or molecules is referred to as spectroscopy. A transition from a lower energy level to a higher level with transfer of electromagnetic energy to the atom or molecule is called absorption; a transition from a higher energy level to a lower level is called emission (if energy is transferred to the electromagnetic field); a…
Speech is defined as the ability to convey thoughts, ideas, or other information by means of articulating sound into meaningful words. Many animals can make sounds and some can tailor these sounds to a given occasion. They may sound an alarm that a predator is in the area, warning others of their species that something has trespassed into their territory. Animals may make soothing sounds to let of…
A sphere is a three dimensional figure that is the set of all points equidistant from a fixed point, called the center. The diameter of a sphere is a line segment which passes through the center and whose endpoints lie on the sphere. The radius of a sphere is a line segment whose one endpoint lies on the sphere and whose other endpoint is the center. A great circle of a sphere is the intersection …
Spider monkeys are slender, medium-sized monkeys with long limbs and very long tails. They live in trees, rarely coming down to the jungle floor. They are very adept at moving around in trees with the help of their prehensile tails; "prehensile" is a term that means their tails are well adapted for holding on to objects. These monkeys inhabit a territory ranging from southern Mexico …
The spiderwort family (Commelinaceae) is a small family of monocotyledonous (with one seed leaf) plants, found primarily in tropical and desert areas of the world. The family contains 38 genera and about 600 species. All members of the family are herbaceous, and are easily recognized by their simple, linear leaves, and large, brittle nodes. Their flowers are borne either on a terminal inflorescenc…
Spin, s, is the rotation of a particle on its axis, as the earth spins on its axis. The spin of a particle is also called intrinsic angular momentum. Angular momentum is momentum (mass times velocity) times the perpendicular lever arm (distance between point of rotation and application of force). An intrinsic property is one that depends on the essential nature of an object. The total angular mome…
Spina bifida is a congenital neural tube defect caused by problems with the early development of the spinal cord. The main defect of spina bifida is the failure of closure of the vertebral column (the bony column surrounding the spinal cord) during embryogenesis. Embryogenesis refers to the stages of a developing embryo after fertilization of the egg by the sperm. Without closure of the neural tub…
The best known species is Spinacia oleracea. Two varieties are grown extensively, one with smooth leaves and another wrinkled, savoy variety. Both of these can be purchased fresh at produce stores. In the food packing industry, the smooth-leaved type is usually canned or frozen before shipping, and the savoy variety is packaged and shipped fresh. Spinach grows best in cool, temperate weather. Cool…
The spiny anteaters, or echidnas, make up five of the six species in the order Monotremata. These are primitive mammals that lay eggs like reptiles but have hair and suckle their young. One species of spiny anteater, Tachyglossus aculeatus, lives in Australia, Tasmania, and New Guinea. A second, T. setosus, is slightly larger and resides only in Tasmania. The other three species (in the genus Zagl…
The spiny eel, belonging to the order Notacanthiformes and the family Notacanthidae, is an eel-like fish that grows to more than 3.3 ft (1 m) long and lives in the north Atlantic Ocean. It has a series of short, thick spines on its back, and there are about 20 slender spines preceding its anal fin on its underside. This fish is a benthic fish, meaning that it lives close to or on the bottom of the…
Spiny-headed worms, or arrow worms as they are also known, belong to the phylum Chaetognatha. Their bodies are shaped like a torpedo with distinct head, trunk, and tail regions, the latter which bears a pair of finlike projections that probably assist with balance. Although many spiny-headed worms can swim, they usually conserve their energy and instead drift with the water current. The body is us…
The spirometer is an instrument used in medicine to measure the volume of air inhaled and exhaled. The device is considered an essential tool in the detection of chronic obstructive pulmonary disease, which includes emphysema and chronic bronchitis. Chronic obstructive pulmonary disease was the fourth most common cause of death in the United States in 1993. In addition, spirometers are typically u…
Sponges are the most primitive multicellular organisms that possess no proper organs. All members of this phylum (Porifera) are permanently attached to another surface, such as rocks, corals, or shells. More than 10,000 species have been described to date. Although some species occur in freshwater, the vast majority are marine, living mainly in shallow tropical waters. A wide range of forms occur …
Spontaneous generation, also called abiogenesis, is the belief that some living things can arise suddenly, from inanimate matter, without the need for a living progenitor to give them life. Through the centuries, the notion of spontaneous generation gave rise to a wide variety of exotic beliefs, such as that snakes could arise from horse hairs standing in stagnant water, mice from decomposing fodd…
In zoology, spores are structures that are used by organisms to survive a period of unfavorable environmental conditions, and can subsequently regenerate into the adult form once the environment again becomes favorable for growth. Depending on the species, spores are asexual, resting bodies, which can be one-celled or multi-cellular. Many protozoans have a stage in their life cycle that involves t…
"What do they know of cricket who only cricket know?" queried the historian and political reformer C. L. R. James in the preface of Beyond a Boundary (1963), his lyrical exploration of political, social, and racial relations in the twentieth-century West Indies and British Empire. He answered throughout the book that those who only know sport really know nothing of value. Sport, he i…
Springtails are tiny insects in the order Collembola, a relatively ancient and primitive group in the sub-class of wingless insects known as Apterygota. Springtails have a fossil record extending back to the Devonian era, some 400 million years ago. Collembolans undergo complete metamorphosis, where the immature stages (nymphs) are tiny representations of the adult. Springtails are named for their…
Spruces are species of trees in the genus Picea, family Pinaceae. The natural range of spruces is the Northern Hemisphere, where these trees occur in boreal and cool-temperate climates. These climates are common at high altitudes on the slopes of mountains and at high latitudes towards the north, south of the arctic tundra. Spruces sometimes dominate the forests in which they occur, or sometimes t…
Squid is the common name for a group of marine mollusks (order Mollusca) with highly developed eyes and brain, and complex swimming behavior. About one-half the length (24-36 in; 60-90 cm) of the common North Atlantic species Loligo pealei consists of its streamlined cylindrical body, and the other half is its set of eight arms and two arm-like tentacles. These appendages are equipped with small s…
Squirrel fish, belonging to the order Beryciformes, are brightly colored, medium-sized fish that are active mostly at night. Squirrel fish live in rocky or coral reefs in tropical and warm temperate seas. Their most distinguishing characteristics are their large eyes and their ability to make sounds to ward off intruders. The order Beryciformes is composed of 15 families and about 150 species of m…
The squirrel family (Sciuridae) is a diverse group of about 50 genera of rodents, including the "true" or tree squirrels, as well as flying squirrels, ground squirrels, chipmunks, marmots, woodchuck, and prairie dogs. Members of the squirrel family occur in North and South America, Africa, Eurasia, and Southeast Asia, but not in Madagascar, New Guinea, Australia, or New Zealand. The …
Stalactites and stalagmites are speleothems formed by water dripping or flowing from fractures on the ceiling of a cave. In caves, stalagmites grow rather slowly (0.00028-0.0366 in/yr [0.007-0.929 mm/yr]), while in artificial tunnels and basements they grow much faster. Soda straw stalactites are the fastest growing (up to 40 mm/yr.), but most fragile stalactites in caves. Soda straw stalactites f…
The Standard Model is the complete catalogue of fundamental particles known to physicists at this time. It gives a complete account of the irreducible piece-parts or "fundamental particles" of which all matter and force are made, so far as those particles are known at this time. The Standard Model is not an all-embracing "theory of everything," however, because it does …
A star is a hot, roughly spherical ball of gas that shines as a result of nuclear fusion reactions in its core. Stars are the fundamental objects in the universe. They are the factories where elements heavier than hydrogen are formed. The radiation from a typical star like the Sun provides temperate conditions on planets like Earth where life can arise. Since the Sun is obviously the central sourc…
Star clusters are groups of stars that occur close to each other in space, appear to have roughly similar ages, and therefore, seem to have had a common origin. Star clusters are typically classified into one of two large subgroups, galactic clusters and globular clusters. Galactic clusters are sometimes also known as open clusters. Astronomers have identified thousands of galactic star clusters i…
Billions of large, essentially independent groups of stars exist in the universe. These are called galaxies. A galaxy is labeled a starburst galaxy if an exceptionally high rate of star formation is found to be taking place within it. This often occurs in galaxies that are in the process of or have recently undergone a merging or collision with another galaxy. Although astronomers do not know exac…
Starfish are marine invertebrates in the phylum Echinodermata, which also includes sea urchins, brittle stars, sea lilies, and sea cucumbers. Starfish belong to the class Asteroidea, which includes 1,500 species inhabiting the shallow margins of all of the world's oceans. Starfish vary widely in appearance. Some species grow up to 3 ft (1 m) in diameter; others are barely 0.5 in (1.3 cm) ac…
Starlings are robust, stocky song birds in the family Sturnidae. They have a stout beak and strong legs, and are included with other perching birds in the order Passeriformes. There are about 110 species of starlings, whose natural range includes Eurasia, Africa, the Pacific islands, and Australia. Starlings are small- to medium-sized birds, ranging in body length from about 4-17 in (10-43 cm), an…
The concept of the state was central to the social sciences until temporarily displaced in the 1950s by a concept of the "political system" that is mainly associated with Talcott Parsons's (1902–1979) systems analysis. Parsons's sociology identified the political system with behaviors and institutions that provide a center of integration for all aspects of the so…
The state of nature is a situation without government, employed in social contract theory in order to justify political authority. The device is most important in the works of the great contract theorists of the seventeenth and eighteenth centuries, mainly Thomas Hobbes (1588–1679), John Locke (1632–1704), and Jean-Jacques Rousseau (1712–1778). But it has a long history and wa…
Was there a moment of creation for the universe, or has the universe always existed? The steady-state theory is a cosmological theory for the origin of the universe that suggests the universe has always existed and did not have a moment of creation. This theory was popular during the 1950s and 1960s, but because of observations made during the 1960s, few, if any, astronomers now think that the ste…
Steam pressure sterilization requires a combination of pressure, high temperatures, and moisture, and serves as one of the most widely used methods for sterilization where these functions will not effect a load. The simplest example of a steam pressure sterilizer is a home pressure cooker, though it is not recommended for accurate sterilization. Its main component is a chamber or vessel in which i…
Stearic acid is a chemical compound consisting of an 18 carbon chain whose terminal carbon is connected to an oxygen atom with a double bond and a hydroxyl group (OH) by a single bond. It belongs to class of materials known as fatty acids, produced primarily from natural fats and oils. Stearic acid is an important component in soap and other cosmetic and industrial preparations. Stearic acid is de…
Steel is the most widely used of all metals, with uses ranging from concrete reinforcement in highways and in high-rise buildings to automobiles, aircraft, and vehicles in space. Steel is iron combined or alloyed with other metals or nonmetals such as carbon. Steel is more ductile (able to deform without breakage) and durable than cast iron and is generally forged, rolled, or drawn into various sh…
Stellar magnetic fields are an array of forces that can be observed surrounding and at the surfaces of stars like the Sun. They are similar in nature to the effect of the well-known dipolar magnets found in science laboratories, classrooms, and toys, but far more powerful and infinitely more complex. They are an important part of the physical makeup of stars because they affect their interiors, at…
Stars fall into distinct groups or populations. The basic stellar populations are Population I stars and Population II stars. The sun and most stars near the sun are Population I stars. They are young second- to third-generation stars with compositions that include 2% of elements heavier than hydrogen and helium. Population II stars, on the other hand, are older stars whose compositions are just h…
It is said that Fred Hoyle once described the evolution of a star as a continual war between nuclear physics and gravity. The structure of a star can be characterized as a polarized battle in that war. The gravity of the stellar material pulls on all the other stellar material striving to bring about a collapse. However, the gravity is opposed by the internal pressure of the stellar gas which norm…
Stem cells are undifferentiated cells that have the capability of self replication as well as being able to give rise to diverse types of differentiated or specialized cell lines. Stem cells are subclassified as embryonic stem cells, embryonic germ cells, or adult stem cells. Embryonic stem cells are cultured cells that were originally collected from the inner cell mass of an embryo at the blastoc…
Sticklebacks are small, bony fish in the family Gasterosteidae that rarely exceed 3 in (8 cm) in body length. Instead of scales, these fish have bony plates covering their body. Sticklebacks are found in North America and northern Eurasia. The name stickleback is derived from the sharp, thick spines arising in the first dorsal fin. The number of these spines forms part of the basis for the identif…
Stilts and avocets are long-legged, long-beaked wading birds of the muddy shores of shallow lakes and lagoons, including both fresh and saline waters. There are fewer than ten species of stilts and avocets all of which are included in the family Recurvirostridae. These birds occur in the temperate and tropical zones of all of the continents except Antarctica. The bill of stilts is rather straight,…
The term stimulus has many meanings; very generally, it is any occurrence (be it an external event, or anything perceived or thought) that causes a detectable response. Stimulus is often used with qualifying terms to further specify its meaning, for example, conditioned stimulus and neutral stimulus. Various fields of study use the term stimulus in different ways. In psychology, it is most often u…