In electrical engineering, treeing is an electrical pre-breakdown phenomenon in solid insulation. It is a damaging process due to partial discharges and progresses through the stressed dielectric insulation, in a path resembling the branches of a tree. Treeing of solid high-voltage cable insulation is a common breakdown mechanism and source of electrical faults in underground power cables. Electrical treeing first occurs and propagates when a dry dielectric material is subjected to high and divergent electrical field stress over a long period of time. Electrical treeing is observed to originate at points where impurities, gas voids, mechanical defects, or conducting projections cause excessive electrical field stress within small regions of the dielectric; this can ionize gases within voids inside the bulk dielectric, creating small electrical discharges between the walls of the void. An impurity or defect may result in the partial breakdown of the solid dielectric itself. Ultraviolet light and ozone from these partial discharges react with the nearby dielectric and further degrading its insulating capability.
Gases are liberated as the dielectric degrades, creating new voids and cracks. These defects further weaken the dielectric strength of the material, enhance the electrical stress, accelerate the PD process. In the presence of water, a diffuse conductive 3D plume-like structure, called a water tree, may form within the polyethylene dielectric used in buried or water-immersed high voltage cables; the plume is known to consist of a dense network of small water-filled channels which are defined by the native crystalline structure of the polymer. Individual channels are difficult to see using optical magnification, so their study requires using a scanning electron microscope. Water trees begin as a microscopic region near a defect, they grow under the continued presence of a high electrical field and water. Water trees may grow to the point where they bridge the outer ground layer to the center high voltage conductor, at which point the stress redistributes across the insulation. Water trees are not a reliability concern unless they are able to initiate an electrical tree.
Another type of tree-like structure can form with or without the presence of water is called an electrical tree. It forms within a polyethylene dielectric. Electrical trees originate where bulk or surface stress enhancements initiate dielectric breakdown in a small region of the insulation; this permanently damages the insulating material in that region. Further tree growth occurs through as additional small electrical breakdown events. Electrical tree growth may be accelerated by rapid voltage changes, such as utility switching operations. Cables injected with high voltage DC may develop electrical trees over time as electrical charges migrate into the dielectric nearest the HV conductor; the region of injected charge amplifies the electrical field in the dielectric, stimulating further stress enhancement and the initiation of electrical trees as the site of pre-existing stress enhancements. Since the electrical tree itself is partially conducting, its presence increases the electrical stress in the region between the tree and the opposite conductor.
Unlike water trees, the individual channels of electrical trees are larger and more seen. Treeing has been a long-term failure mechanism for buried polymer-insulated high voltage power cables, first reported in 1969. In a similar fashion, 2D trees can occur along the surface of a stressed dielectric, or across a dielectric surface, contaminated by dust or mineral salts. Over time, these conductive trails can grow until they cause complete failure of the dielectric. Electrical tracking, sometimes called dry banding, is a typical failure mechanism for electrical power insulators that are subjected to salt spray contamination along coastlines; the branching 2D and 3D patterns are sometimes called Lichtenberg figures. Electrical treeing or "Lichtenberg figures" occur in high-voltage equipment just before breakdown. Following these Lichtenberg figures in the insulation during postmortem investigation of the broken down insulation can be most useful in finding the cause of breakdown. An experienced high-voltage engineer can see from the direction and the type of trees and their branches where the primary cause of the breakdown was situated and find the cause.
Broken-down transformers, high-voltage cables and other equipment can usefully be investigated in this way. Electrical trees can be further categorized depending on the different tree patterns; these include dendrites, branch type, bush type, strings, bow-ties and vented trees. The two most found tree types are bow-tie trees and vented trees. Bow-tie trees Bow-tie trees are trees which start to grow from within the dielectric insulation and grow symmetrically outwards toward the electrodes; as the trees start within the insulation, they have no free supply of air which will enable continuous support of partial discharges. Thus, these trees have discontinuous growth, why the bow-tie trees do not grow long enough to bridge the entire insulation between the electrodes, therefore causing no failure in the insulation. Vented trees Vented trees are trees which initiate at an electrode insulation interface and grow towards the opposite electrode. Having access to free a
In mathematics, a fractal is a subset of a Euclidean space for which the Hausdorff dimension exceeds the topological dimension. Fractals tend to appear nearly the same at different levels, as is illustrated here in the successively small magnifications of the Mandelbrot set. Fractals exhibit similar patterns at small scales called self similarity known as expanding symmetry or unfolding symmetry. One way that fractals are different from finite geometric figures is the way. Doubling the edge lengths of a polygon multiplies its area by four, two raised to the power of two. If the radius of a sphere is doubled, its volume scales by eight, two to the power of three. However, if a fractal's one-dimensional lengths are all doubled, the spatial content of the fractal scales by a power, not an integer; this power is called the fractal dimension of the fractal, it exceeds the fractal's topological dimension. Analytically, fractals are nowhere differentiable. An infinite fractal curve can be conceived of as winding through space differently from an ordinary line – although it is still 1-dimensional, its fractal dimension indicates that it resembles a surface.
Starting in the 17th century with notions of recursion, fractals have moved through rigorous mathematical treatment of the concept to the study of continuous but not differentiable functions in the 19th century by the seminal work of Bernard Bolzano, Bernhard Riemann, Karl Weierstrass, on to the coining of the word fractal in the 20th century with a subsequent burgeoning of interest in fractals and computer-based modelling in the 20th century. The term "fractal" was first used by mathematician Benoit Mandelbrot in 1975. Mandelbrot based it on the Latin frāctus, meaning "broken" or "fractured", used it to extend the concept of theoretical fractional dimensions to geometric patterns in nature. There is some disagreement among mathematicians about how the concept of a fractal should be formally defined. Mandelbrot himself summarized it as "beautiful, damn hard useful. That's fractals." More formally, in 1982 Mandelbrot stated that "A fractal is by definition a set for which the Hausdorff–Besicovitch dimension exceeds the topological dimension."
Seeing this as too restrictive, he simplified and expanded the definition to: "A fractal is a shape made of parts similar to the whole in some way." Still Mandelbrot settled on this use of the language: "...to use fractal without a pedantic definition, to use fractal dimension as a generic term applicable to all the variants". The consensus is that theoretical fractals are infinitely self-similar and detailed mathematical constructs having fractal dimensions, of which many examples have been formulated and studied in great depth. Fractals are not limited to geometric patterns, but can describe processes in time. Fractal patterns with various degrees of self-similarity have been rendered or studied in images and sounds and found in nature, art and law. Fractals are of particular relevance in the field of chaos theory, since the graphs of most chaotic processes are fractals; the word "fractal" has different connotations for laymen as opposed to mathematicians, where the layman is more to be familiar with fractal art than the mathematical concept.
The mathematical concept is difficult to define formally for mathematicians, but key features can be understood with little mathematical background. The feature of "self-similarity", for instance, is understood by analogy to zooming in with a lens or other device that zooms in on digital images to uncover finer invisible, new structure. If this is done on fractals, however, no new detail appears. Self-similarity itself is not counter-intuitive; the difference for fractals is. This idea of being detailed relates to another feature that can be understood without mathematical background: Having a fractal dimension greater than its topological dimension, for instance, refers to how a fractal scales compared to how geometric shapes are perceived. A regular line, for instance, is conventionally understood to be one-dimensional. A solid square is understood to be two-dimensional. We see that for ordinary self-similar objects, being n-dimensional means that when it is rep-tiled into pieces each scaled down by a scale-factor of 1/r, there are a total of rn pieces.
Now, consider the Koch curve. It can be rep-tiled into four sub-copies, each scaled down by a scale-factor of 1/3. So by analogy, we can consider the "dimension" of the Koch curve as being the unique real number D that satisfies 3D = 4, which by no means is an integer! This number is; the fact th
Heinrich Rudolf Hertz was a German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell's electromagnetic theory of light. The unit of frequency, cycle per second, was named the "Hertz" in his honor. Heinrich Rudolf Hertz was born in 1857 in Hamburg a sovereign state of the German Confederation, into a prosperous and cultured Hanseatic family, his father was Gustav Ferdinand Hertz. His mother was Anna Elisabeth Pfefferkorn. While studying at the Gelehrtenschule des Johanneums in Hamburg, Hertz showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit, he studied sciences and engineering in the German cities of Dresden and Berlin, where he studied under Gustav R. Kirchhoff and Hermann von Helmholtz. In 1880, Hertz obtained his PhD from the University of Berlin, for the next three years remained for post-doctoral study under Helmholtz, serving as his assistant. In 1883, Hertz took a post as a lecturer in theoretical physics at the University of Kiel.
In 1885, Hertz became a full professor at the University of Karlsruhe. In 1886, Hertz married Elisabeth Doll, the daughter of Dr. Max Doll, a lecturer in geometry at Karlsruhe, they had two daughters: Johanna, born on 20 October 1887 and Mathilde, born on 14 January 1891, who went on to become a notable biologist. During this time Hertz conducted his landmark research into electromagnetic waves. Hertz took a position of Professor of Physics and Director of the Physics Institute in Bonn on 3 April 1889, a position he held until his death. During this time he worked on theoretical mechanics with his work published in the book Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt, published posthumously in 1894. In 1892, Hertz underwent operations to treat the illness, he died of granulomatosis with polyangiitis at the age of 36 in Bonn, Germany in 1894, was buried in the Ohlsdorf Cemetery in Hamburg. Hertz's wife, Elisabeth Hertz née Doll, did not remarry. Hertz left two daughters and Mathilde.
Hertz's daughters never married and he has no descendants. In 1864 Scottish mathematical physicist James Clerk Maxwell, proposed a comprehensive theory of electromagnetism, now called Maxwell's equations. Maxwell's theory predicted that coupled electric and magnetic fields could travel through space as an "electromagnetic wave". Maxwell proposed that light consisted of electromagnetic waves of short wavelength, but no one had been able to prove this, or generate or detect electromagnetic waves of other wavelengths. During Hertz's studies in 1879 Helmholtz suggested that Hertz's doctoral dissertation be on testing Maxwell's theory. Helmholtz had proposed the "Berlin Prize" problem that year at the Prussian Academy of Sciences for anyone who could experimentally prove an electromagnetic effect in the polarization and depolarization of insulators, something predicted by Maxwell's theory. Helmholtz was sure Hertz was the most candidate to win it. Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, worked on electromagnetic induction instead.
Hertz did produce an analysis of Maxwell's equations during his time at Kiel, showing they did have more validity than the prevalent "action at a distance" theories. After Hertz received his professorship at Karlsruhe he was experimenting with a pair of Riess spirals in the autumn of 1886 when he noticed that discharging a Leyden jar into one of these coils would produce a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way to proceed with the "Berlin Prize" problem of 1879 on proving Maxwell's theory, he used a Ruhmkorff coil-driven spark gap and one-meter wire pair as a radiator. Capacity spheres were present at the ends for circuit resonance adjustments, his receiver was a simple half-wave dipole antenna with a micrometer spark gap between the elements. This experiment produced and received what are now called radio waves in the high frequency range. Between 1886 and 1889 Hertz would conduct a series of experiments that would prove the effects he was observing were results of Maxwell's predicted electromagnetic waves.
Starting in November 1887 with his paper "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators", Hertz would send a series of papers to Helmholtz at the Berlin Academy, including papers in 1888 that showed transverse free space electromagnetic waves traveling at a finite speed over a distance. In the apparatus Hertz used, the electric and magnetic fields would radiate away from the wires as transverse waves. Hertz had positioned the oscillator about 12 meters from a zinc reflecting plate to produce standing waves; each wave was about 4 meters long. Using the ring detector, he recorded how the wave's component direction varied. Hertz measured Maxwell's waves and demonstrated that the velocity of these waves was equal to the velocity of light; the electric field intensity and reflection of the waves were measured by Hertz. These experiments established that light and these waves were both a form of electromagnetic radiation obeying the Maxwell equations. Hertz did not realize the practical importance of his radio wave experiments.
He stated that, "It's of no use whatsoever this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."Asked about the applications of his discoveries, Hertz replied, "Nothing, I g
Lightning is a violent and sudden electrostatic discharge where two electrically charged regions in the atmosphere temporarily equalize themselves during a thunderstorm. Lightning creates a wide range of electromagnetic radiations from the hot plasma created by the electron flow, including visible light in the form of black-body radiation. Thunder is the sound formed by the shock wave formed as gaseous molecules experience a rapid pressure increase; the three main kinds of lightning are: created either inside one thundercloud, or between two clouds, or between a cloud and the ground. The 15 recognized observational variants include "heat lightning", seen but not heard, dry lightning, which causes many forest fires, ball lightning, observed scientifically. Humans have deified lightning for millennia, lightning inspired expressions like "Bolt from the blue", "Lightning never strikes twice", "blitzkrieg" are common. In some languages, "Love at first sight" translates as "lightning strike"; the details of the charging process are still being studied by scientists, but there is general agreement on some of the basic concepts of thunderstorm electrification.
The main charging area in a thunderstorm occurs in the central part of the storm where air is moving upward and temperatures range from −15 to −25 °C, see figure to the right. At that place, the combination of temperature and rapid upward air movement produces a mixture of super-cooled cloud droplets, small ice crystals, graupel; the updraft carries the super-cooled cloud droplets and small ice crystals upward. At the same time, the graupel, larger and denser, tends to fall or be suspended in the rising air; the differences in the movement of the precipitation cause collisions to occur. When the rising ice crystals collide with graupel, the ice crystals become positively charged and the graupel becomes negatively charged. See figure to the left; the updraft carries. The larger and denser graupel is either suspended in the middle of the thunderstorm cloud or falls toward the lower part of the storm; the result is that the upper part of the thunderstorm cloud becomes positively charged while the middle to lower part of the thunderstorm cloud becomes negatively charged.
The upward motions within the storm and winds at higher levels in the atmosphere tend to cause the small ice crystals in the upper part of the thunderstorm cloud to spread out horizontally some distance from thunderstorm cloud base. This part of the thunderstorm cloud is called the anvil. While this is the main charging process for the thunderstorm cloud, some of these charges can be redistributed by air movements within the storm. In addition, there is a small but important positive charge buildup near the bottom of the thunderstorm cloud due to the precipitation and warmer temperatures. A typical cloud-to-ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 km tall, from within the cloud to the ground's surface; the actual discharge is the final stage of a complex process. At its peak, a typical thunderstorm produces three or more strikes to the Earth per minute. Lightning occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarizing the atmosphere.
However, it can occur during dust storms, forest fires, volcanic eruptions, in the cold of winter, where the lightning is known as thundersnow. Hurricanes generate some lightning in the rainbands as much as 160 km from the center; the science of lightning is called fulminology, the fear of lightning is called astraphobia. Lightning is not distributed evenly around the planet. On Earth, the lightning frequency is 44 times per second, or nearly 1.4 billion flashes per year and the average duration is 0.2 seconds made up from a number of much shorter flashes of around 60 to 70 microseconds. Many factors affect the frequency, distribution and physical properties of a typical lightning flash in a particular region of the world; these factors include ground elevation, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may vary by season in middle latitudes; because human beings are terrestrial and most of their possessions are on the Earth where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types though IC and CC are more common types of lightning.
Lightning's relative unpredictability limits a complete explanation of how or why it occurs after hundreds of years of scientific investigation. About 70 % of lightning occurs over land in the tropics; this occurs from both the mixture of warmer and colder air masses, as well as differences in moisture concentrations, it happens at the boundaries between them. The flow of warm ocean currents past drier land masses, such as the Gulf Stream explains the elevated frequency of lightning in the Southeast United States; because the influence of small or absent land masses in the vast stretches of the world's oceans limits the differences between these variants in the atmosphere, lightning is notably less frequent there than over larger landforms. The North and South Poles are limited in their coverage of thunderstorms and theref
Diffusion-limited aggregation is the process whereby particles undergoing a random walk due to Brownian motion cluster together to form aggregates of such particles. This theory, proposed by T. A. Witten Jr. and L. M. Sander in 1981, is applicable to aggregation in any system where diffusion is the primary means of transport in the system. DLA can be observed in many systems such as electrodeposition, Hele-Shaw flow, mineral deposits, dielectric breakdown; the clusters formed in DLA processes are referred to as Brownian trees. These clusters are an example of a fractal. In 2D these fractals exhibit a dimension of 1.71 for free particles that are unrestricted by a lattice, however computer simulation of DLA on a lattice will change the fractal dimension for a DLA in the same embedding dimension. Some variations are observed depending on the geometry of the growth, whether it be from a single point radially outward or from a plane or line for example. Two examples of aggregates generated using a microcomputer by allowing random walkers to adhere to an aggregate are shown on the right.
Computer simulation of DLA is one of the primary means of studying this model. Several methods are available to accomplish this. Simulations can be done on a lattice of any desired geometry of embedding dimension or the simulation can be done more along the lines of a standard molecular dynamics simulation where a particle is allowed to random walk until it gets within a certain critical range whereupon it is pulled onto the cluster. Of critical importance is that the number of particles undergoing Brownian motion in the system is kept low so that only the diffusive nature of the system is present; the intricate and organic forms that can be generated with diffusion-limited aggregation algorithms have been explored by artists. Simutils, part of the toxiclibs open source library for the Java programming language developed by Karsten Schmidt, allows users to apply the DLA process to pre-defined guidelines or curves in the simulation space and via various other parameters dynamically direct the growth of 3D forms.
The electron is a subatomic particle, symbol e− or β−, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, are thought to be elementary particles because they have no known components or substructure; the electron has a mass, 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant, ħ; as it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light; the wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy. Electrons play an essential role in numerous physical phenomena, such as electricity, magnetism and thermal conductivity, they participate in gravitational and weak interactions.
Since an electron has charge, it has a surrounding electric field, if that electron is moving relative to an observer, it will generate a magnetic field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law. Electrons absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications such as electronics, cathode ray tubes, electron microscopes, radiation therapy, gaseous ionization detectors and particle accelerators. Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics; the Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms.
Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge'electron' in 1891, J. J. Thomson and his team of British physicists identified it as a particle in 1897. Electrons can participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere; the antiparticle of the electron is called the positron. When an electron collides with a positron, both particles can be annihilated, producing gamma ray photons.
The ancient Greeks noticed. Along with lightning, this phenomenon is one of humanity's earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electrica, to refer to those substances with property similar to that of amber which attract small objects after being rubbed. Both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον. In the early 1700s, Francis Hauksbee and French chemist Charles François du Fay independently discovered what they believed were two kinds of frictional electricity—one generated from rubbing glass, the other from rubbing resin. From this, du Fay theorized that electricity consists of two electrical fluids and resinous, that are separated by friction, that neutralize each other when combined. American scientist Ebenezer Kinnersley also independently reached the same conclusion. A decade Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess or deficit.
He gave them the modern charge nomenclature of negative respectively. Franklin thought of the charge carrier as being positive, but he did not identify which situation was a surplus of the charge carrier, which situation was a deficit. Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges. Beginning in 1846, German physicist William Weber theorized that electricity was composed of positively and negatively charged fluids, their interaction was governed by the inverse square law. After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion, he was able to estimate the value of this elementary charge e by means of Faraday's laws of electrolysis. However, Stoney could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity".
Stoney coined the term
A golf course is the grounds where the game of golf is played. It comprises a series of holes, each consisting of a teeing ground, a fairway, the rough and other hazards, a green with a flagstick and hole. A standard round of golf consists of 18 holes. Most courses contain 18 holes. Par-3 courses consist of 18 holes all of which have a par of three strokes. Many older courses are links coastal. Courses are private and municipally owned, feature a pro shop. Many private courses are found at country clubs. Although a specialty within landscape design or landscape architecture, golf course architecture is considered a separate field of study; some golf course architects become celebrities in their own right, such as Robert Trent Jones, Jr.. The field is represented by the American Society of Golf Course Architects, the European Institute of Golf Course Architects, the Society of Australian Golf Course Architects, although many of the finest golf course architects in the world choose not to become members of any such group, as associations of architects are not government-sanctioned licensing bodies, but private groups.
While golf courses follow the original landscape, some modification is unavoidable. This is the case as new courses are more to be sited on less optimal land. Bunkers and sand traps are always artificial, although other hazards may be natural; the layout of a course follows certain traditional principles, such as the number of holes, their par values, the number of holes of each par value per course. It is preferable to arrange greens to be close to the tee box of the next playable hole, to minimize travel distance while playing a round, to vary the mix of shorter and longer holes. Combined with the need to package all the fairways within what is a compact square or rectangular plot of land, the fairways of a course tend to form an oppositional tiling pattern. In complex areas, two holes may share the same tee box, fairway, or green, it is common for separate tee-off points to be positioned for men and amateurs, each one lying closer to the green. Eighteen-hole courses are traditionally broken down into a "front 9" and a "back 9".
On older courses, the holes may be laid out in one long loop and ending at the clubhouse, thus the front 9 is referred to on the scorecard as "out" and the back 9 as "in". More recent courses tend to be designed with the front 9 and the back 9 each constituting a separate loop beginning and ending at the clubhouse; this is for the convenience of the players and the club, as it is easier to play just a 9-hole round, if preferred, or stop at the clubhouse for a snack between the front 9 and the back 9. A successful design is as visually pleasing. With golf being a form of outdoor recreation, the strong designer is an adept student of natural landscaping who understands the aesthetic cohesion of vegetation, water bodies, grasses and woodwork, among other elements. Most golf courses have only par-3, −4, −5 holes, although some courses include par-6 holes; the Ananti CC and the Satsuki golf course in Sano, Japan are the only courses with par 7 holes. Typical distances for the various holes from standard tees are as follows.
Men Par 3 – 250 yards and below Par 4 – 251–450 yards Par 5 – 451–690 yards Women Par 3 – 210 yards and below Par 4 – 211–400 yards Par 5 – 401–575 yards Harder or easier courses may have longer- or shorter-distance holes, respectively. Terrain can be a factor, so that a long downhill hole might be rated par 4, but a shorter uphill or treacherous hole might be rated par 5. Tournament players will play from a longer-distance tee box, behind the standard men's tee, which increases the typical distance of each par; this compensates for the longer distance pro players can put on tee and fairway shots as compared to the average "bogey golfer". The game of golf is played in what is called a "round"; this consists of playing a set number of holes in an order predetermined by the course. When playing on an 18-hole course, each hole is played once. To begin a hole, players start by striking the ball off a tee. Playing the ball off a tee can only be used on the first shot of every hole although it is not required to use a tee on the first shot.
Tees are a small wooden or plastic peg used to hold the ball up, so that when hit by the club the ball travels as far as possible. The first section of every hole consists of tee-box. There is more than one available box where a player places his ball, each one a different distance from the hole to provide differing difficulty; the teeing ground is as level as feasible, with mown grass similar to that of a putting green, most are raised from the surrounding fairway. Each tee box has