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Normal Force

Normal force

In physics, the normal force (F_N) is the perpendicular component of the contact force exerted by, for example, the surface of a floor or wall, on an object, preventing the object from entering the floor or wall. In a static situation it is just enough to balance the force with which the object pushes, e.g. its weight on the floor, or a smaller force if somebody leans against a wall. If an object hits the surface with some speed, the normal force provides for a rapid deceleration, depending on how flexible the floor/wall is (and, of course, if it can provide enough force instead of breaking). Also, if the object is soft, only the outer part needs to decelerate rapidly, the inner part can do that more gradually, while the layer in between is compressed. Note that the sign of the calculated value will be either positive or negative depending upon whether the positive Y-axis is taken to be either positive or negative. In general, the normal force density is the dot product of a unit normal with the stress tensor describing the stress state of the surface.

Frictional force

The parallel shear component of the contact force is known as the frictional force (F_f).

Example

In a simple case such as a 40 kg object resting upon a table, the normal force from the table to the object is equal but in opposite direction to the force applied to the table by the object (i.e., weight of the object). In this case the normal force is given by, 40 kg · 9.81 m/s²=392.4 newtons where 9.81 m/s² is equal to the acceleration due to gravity (near the Earth's surface).

Real world applications

In an upwardly accelerating elevator, the normal force does not only balance the weight, but also provides upward acceleration to the person standing in the elevator, preventing him/her from staying behind and passing through the floor of the elevator. Category:Statics Category:Introductory physics ko:%EC%88%98%EC%A7%81%ED%95%AD%EB%A0%A5

Contact force

In physics, a contact force is a force between two objects (or an object and a surface) that are in contact with each other. This is distinct from a force that acts over a distance, such as gravity or magnetic attraction/repulsion. A contact force has two components. The part of the force that lies within the plane of contact is friction, which must be overcome for the two objects to slide relative to one another along that plane. The part of the force that is perpendicular to the plane of contact is called the normal force. As a consequence of Newton's Third Law, the normal force experienced by each object in contact is equal in magnitude. Strictly speaking, contact forces are only a useful simplification for introductory physics classes and other applications of classical mechanics. Everyday objects on Earth do not actually touch each other; rather contact forces are the result of the interactions of the electrons at or near the surfaces of the objects. Category:Introductory physics

Stress (physics)

In physics, stress is the internal distribution of forces within a body that balance and react to the loads applied to it. Stress is a tensor quantity with nine terms, but can be described fully by six terms due to symmetry. Simplifying assumptions are often used to represent stress as a vector for engineering calculations. The stress in an axially loaded bar is equal to the applied force divided by the bar's area (see also pressure). Stresses in a 2-D or 3-D solid are more complex and need to be defined more rigorously. The internal force acting on a small area dA of a plane that passes through a point P can be resolved into three components: one normal to the plane and two parallel to the plane. The normal component divided by dA gives the normal stress (usually denoted by σ), and the parallel components divided by the area dA give the shear stress (usually denoted by τ). These stresses are average stresses, as the area dA is finite; but when the area dA is allowed to approach zero, the stresses become stresses at the point P. In general, the stress may vary from point to point, but for simple cases, such as circular cylinders with pure axial loading, the stress normal to the cross section is constant. Since stresses are defined in relation to the plane that passes through the point under consideration, and the number of such planes is infinite, there appear an infinite set of stresses at a point P. Fortunately, it can be proven by equilibrium that the stresses on any plane can be computed from the stresses on three orthogonal planes passing through the point. The three planes are normally chosen to be the x-, y-, and z-planes. As each plane has three stresses, the stress tensor has nine stress components, which completely describe the state of stress at a point. By using Mohr's circle method or stress tensor transformation, the stresses on an arbitrary plane through P can be computed from the stress tensor at P. Stress can occur in liquids, gases, and solids. Liquids and gasses support normal stress (pressure), but flow under shear stress (see viscosity). Solids support both shear and normal stress, with brittle materials failing under normal stress, and plastic or ductile materials failing under shear stress.

Stress in one-dimensional bodies

The idea of stress originates in two simple, but important, observations of the loading (in tension) of a one-dimensional body, for example, a steel wire. # When a wire is pulled tight, it stretches (undergoes strain). Up to a certain limit, the amount it stretches is proportional to the load divided by the cross-sectional area of the wire, σ = F/A. # Failure occurs when the load exceeds a critical value for the material, the tensile strength multiplied by the cross-sectional area of the wire, F_c = σ_t A. These observations suggest that the fundamental characteristic that affects the deformation and failure of materials is stress, force divided by the area over which it is applied. This definition of stress, σ = F/A, is sometimes called engineering stress and is used for rating the strength of materials loaded in one dimension. The cross-sectional area is measured prior to applying strain for testing. Poisson's ratio, however, reveals that any applied strain will produce a change in the area, A. Engineering stress neglects this change in area. Stress-strain diagrams are usually presented as engineering stress, even though the sample may undergo a substantial change in cross-sectional area during testing. True stress is a definition of stress that includes the change in cross-sectional area. This is true in the sense that, once you stretch a material it tends to contract in the transverse direction (Poisson contraction) so the actual force per unit area is over that new (usually smaller) area. For engineering applications, the initial geometry is known, so calculations are generally easier in terms of the initial area, hence engineering stress. The distinction between engineering and true stresses is especially important for rubber-like substances and for plasticity, since in these cases the changes in cross-sectional areas can be significant. In the case of small strains, cross-sectional area effectively does not change in which case true and engineering stresses are identical. Both engineering stress and true stress are evaluated as tensors for three-dimensional cases. An example; a steel bolt of diameter 5 mm, has a cross-sectional area of 19.6 mm². A load of 50 N induces a stress (force distributed over the cross section) of σ = 50/19.6 = 2.55 MPa (N/mm²). This can be thought of as each square millimeter of the bolt supporting 2.55 N of the total load. In another bolt with half the diameter, and hence a quarter the cross-sectional area, carrying the same 50 N load, the stress will be quadrupled (10.2 MPa). The ultimate tensile strength is a property of a material loaded in one dimension. It allows the calculation of the load that would cause fracture. The compressive strength is a similar property for compressive loads. The yield tensile strength is the value of stress causing plastic deformation. These values are determined experimentally using the measurement procedure known as the tensile test.

Cauchy's principle

Augustin Louis Cauchy enunciated the principle that, within a body, the forces that an enclosed volume imposes on the remainder of the material must be in equilibrium with the forces upon it from the remainder of the body. This intuition provides a route to characterizing and calculating complicated patterns of stress. To be exact, the stress at a point may be determined by considering a small element of the body that has an area ΔA, over which a force ΔF acts. By making the element infinitesimally small, the stress vector σ is defined as the limit: :

\sigma = \lim_ \frac   =

Being a vector, the stress has two components, one in the plane of the area A, the shear stress, and one perpendicular, the normal stress. The shear stress can be further decomposed into two orthogonal components within the plane, thus giving rise to three stress components acting on this plane.

Plane stress

Plane stress is a two-dimensional state of stress (Figure 2). This 2-D state models well the state of stresses in a flat, thin plate loaded in the plane of the plate. Figure 2 shows the stresses on the x- and y-faces of a differential element. Not shown in the figure are the stresses in the opposite faces and the external forces acting on the material. Since moment equilibrium of the differential element shows that the shear stresses on the perpendicular faces are equal, the 2-D state of stresses is characterized by three independent stress components (σ_x, σ_y, τ_xy). vector

Principal stresses

Cauchy was the first to demonstrate that at a given point, it is always possible to locate two orthogonal planes in which the shear stress vanishes. These planes are called the principal planes, while the normal stresses on these planes are the principal stresses. The common technique for doing this is by use of Mohr's circle. Principal stresses are the maximum and minimum values of the normal stresses. Eigenvalues of a stress tensor show the principal stresses, and the eigenvectors show the direction of the principal stresses.

Mohr's circle

eigenvector eigenvector A graphical representation of any 2-D stress state was proposed by Christian Otto Mohr in 1882. Consider the state of stress at a point P in a body (Figure 2). The Mohr's circle may be constructed as follows. 1. Draw two perpendicular axes with the horizontal axis representing normal stress, while the vertical axis the shear stress. 2. Plot the state of stress on the x-plane as the point A, whose abscissa is the magnitude of the normal stress (tension is positive), and whose ordinate is the shear stress (counterclockwise shear is negative). 3. Mark the magnitude of the normal stress σ_y on the horizontal axis (tension being positive). 4. Mark the midpoint of the two normal stresses, O (Figure 3). 1882 5. Draw the circle with radius OA, centered at O (Figure 4). 6. A point on the Mohr's circle represents the state of stresses on a particular plane at the point P. Of special interest are the points where the circle crosses the horizontal axis, for they represent the magnitudes of the principal stresses (Figure 5).
Mohr's circle may also be applied to three-dimensional stress. In this case, the diagram has three circles, two within a third. Engineers use Mohr's circle to find the planes of maximum normal and shear stresses, as well as the stresses on known weak planes. For example, if the material is brittle, the engineer might use Mohr's circle to find the maximum component of normal stress (tension or compression); and for ductile materials, the engineer might look for the maximum shear stress.

Stress in three dimensions

The considerations above can be generalized to three dimensions. However, this is very complicated, since each shear loading produces shear stresses in one orientation and normal stresses in other orientations, and vice versa. Often, only certain components of stress will be important, depending on the material in question. The von Mises stress is derived from the distortion energy theory and is a simple way to combine stresses in three dimensions to calculate failure criteria of ductile materials. In this way, the strength of material in a 3-D state of stress can be compared to a test sample that was loaded in one dimension.

Stress tensor

Because the behavior of a body does not depend on the coordinates used to measure it, stress can be described by a tensor. The stress tensor is symmetric and can always be resolved into the sum of two symmetric tensors:
- a mean or hydrostatic stress tensor, involving only pure tension and compression; and
- a shear stress tensor, involving only shear stress. In the case of a fluid, Pascal's law shows that the hydrostatic stress is the same in all directions, at least to a first approximation, so can be captured by the scalar quantity pressure. Thus, in the case of a solid, the hydrostatic (or isostatic) pressure p is defined as one third of the trace of the tensor, i.e., the mean of the diagonal terms. :

p = \frac = \frac

Generalized notation

In the generalized stress tensor notation, the tensor components are written σ_ij, where i and j are in . The first step is to number the sides of the cube. When the lines are parallel to a vector base

(\vec,\vec,\vec)

, then:
- the sides perpendicular to

\vec

are called j and -j; and
- from the center of the cube,

\vec

points toward the j side, while the -j side is at the opposite. Figure 6 Cube face nomenclature σ_ij is then the component along the i axis that applies on the j side of the cube. (Or in books in the English language, σ_ij is the stress on the i face acting in the j direction -- the transpose of the subscript notation herein. But transposing the subscript notation produces the same stress tensor, since a symmetric matrix is equal to its transpose.) Figure 6 Cube face nomenclature This generalized notation allows an easy writing of equations of the continuum mechanics, such as the generalized Hooke's law: :

\sigma_ = \sum_ C_ \cdot \varepsilon_

The correspondence with the former notation is thus:

Stress measurement

As with force, stress cannot be measured directly but is usually inferred from measurements of strain and knowledge of elastic properties of the material.

Units

The SI unit for stress is the Pascal (symbol Pa), the same as that of pressure. In US Customary units, stress is expressed in pounds-force per square inch (psi). See also pressure.

Residual stress

Residual stresses are stresses that remain after the original cause of the stresses has been removed. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Castings may also have large residual stresses due to uneven cooling. While uncontrolled residual stresses are undesirable, many designs rely on them. For example, toughened glass and prestressed concrete rely on residual stress to prevent brittle failure. Similarly, a gradient in martensite formation leaves residual stress in some swords with particularly hard edges (notably the katana), which can prevent the opening of edge cracks. In certain types of gun barrels made with two telescoping tubes forced together, the inner tube is compressed while the outer tube stretches, preventing cracks from opening in the rifling when the gun is fired. These tubes are often heated or dunked in liquid nitrogen to aid assembly. Press fits are the most common intentional use of residual stress. Automotive wheel studs, for example, are pressed into holes on the wheel hub. The holes are smaller than the studs, requiring force to drive the studs into place. The residual stresses fasten the parts together. Nails are another example.

Books

- Dieter, G. E. (3 ed.). (1989). Mechanical Metallurgy. New York: McGraw-Hill. ISBN 0071004068.
- Love, A. E. H. (4 ed.). (1944). Treatise on the Mathematical Theory of Elasticity. New York: Dover Publications. ISBN 0486601749.
- Marsden, J. E., & Hughes, T. J. R. (1994). Mathematical Foundations of Elasticity. New York: Dover Publications. ISBN 0486678652.

External links

- [http://documents.wolfram.com/applications/structural/AnalysisofStress.html Stress analysis, Wolfram Research] Category:Continuum mechanics Category:Tensors ko:변형력 ja:ストレス (物理学)

Shear

- In physics and mechanics, shear refers to deformation of a body in which parallel internal surfaces slide past one another (as opposed to compression and tension, in which parallel surfaces move towards or away from one another).
- Shear is also a form of structural failure. A component fails by shearing when it splits into two parts that slide past each other. See shear stress and shear strength.
- In optics, shearing is a simple and very common means to check the collimation of beams by observing interference, see shearing interferometer.
- In the skin shear is the movement of the epidermis over the underlying dermis producing friction, tearing and splitting of the layers. In some cases it can produce hyperkeratosis or rapid skin growth in the area of shear.
- In mathematics, a shear is a particular kind of linear mapping. Mathematical shears are also called transvections.
- In clothing design, fabric may be cut on the shear (also referred to as the bias). This is done by placing the patterns at 45° to the weave of the fabric. Clothing cut on the shear is less stiff and follows the shape of the wearer's body more closely than clothing cut parallel to the weave.
- Wind shear is a difference in wind speed or direction between two wind currents in the atmosphere.
- In lockpicking a cylinder lock, the shear line is where the inner cylinder ends and the outer cylinder begins.
- Sheep-shearing is the process of removing the wool from a sheep.
- In metalworking, a shear is a machine used to cut sheet metal. See guillotine.
- In agriculture and hairdressing a shear is a machine that cuts wool, hair or fur from the body of an animal. The shear can be hand-powered or powered by electricity or other engines. It is normally guided by a person to obtain the effect desired. In shearing farm animals the effect desired is to remove the fleece for processing into fabric, carpet, or similar, and leave the animal able to continue growing another.

Weight

:See also weight function. For the 1994 album by the group Rollins Band, see Weight (album). In the physical sciences, weight is the interaction of matter with a gravitational field. It is equal to the mass of the object multiplied by the magnitude of the gravitational field. The word weight entered Old English sometime around the 9th century, and meant the quantity measured with a balance -- the same as mass in both common and scientific usage. In common usage, weight still means the same as mass.

Weight and mass

"Weight" is often used as a synonym for mass. For instance, when we buy or sell goods "by weight", we are interested in the amount of goods exchanged, not how hard it presses down on the table. Similarly, in measurements of body weight we are primarily interested in the amount of tissue (fat, muscle, etc.) present. Correspondingly, weight is often given in kilograms and other units of mass. In the physical sciences, people usually distinguish between weight and mass. Under most circumstances, this ambiguity is not a problem, because the weight of an object is directly proportional to its mass, and the constant of proportionality -- the strength of the gravitational field -- is approximately constant everywhere on the surface of the Earth (around 9.8 m/s²). For instance, a body will exert less force if it is located on the Moon than if it is on the Earth, since the gravitational field of the Moon is weaker; its mass, on the other hand, does not depend on position. Although terms such as "atomic weight", "molecular weight", and "formula weight" may still be encountered, such usage is often discouraged; terms like atomic mass are used instead. Mass is measured using a balance which compares an item in question to matter of known mass; this method is independent of gravity. Alternately, a spring scale or Hydraulic or pneumatic scale is used to measure force (which physicists call weight). Most scales measure weight using a spring. Related to the historical identification of mass and weight, the pound has been used both as a unit of mass and as a unit of force. In the United States, United Kingdom, and elsewhere, the pound is and always has been officially defined as a unit of mass. The corresponding force is called a pound-force, and similarly the weight of a kilogram of material on Earth is called a kilogram-force. However, the use of pounds to measure forces is still common in engineering, and it occurs in derived units like p.s.i. (pounds per square inch). In most countries, scientists have adopted SI units, which use kilogram for mass and newton for force non-interchangeably.

Weight as a force

The SI unit for weight is the newton (N), or kilogram metres per second squared (kg m s⁻²). The weight force that we sense is actually the normal force exerted by the surface we stand on, which prevents us from being pulled to the center of the Earth, and not the weight itself. This normal force, that we can call the apparent weight is the one that is measured by a weighing scale, not the weight itself. A good evidence of this is given by the fact that a person moving up and down on his toes does see the indicator moving, telling that the measured force is changing while his weight, that depends only on his mass, the Earth mass and the distance between his center of mass and the center of Earth obviously do not change. In contrast, in free-fall, there is no apparent weight because we are not in contact with any surface to provide such a normal force. The experience of having no apparent weight is known as weightlessness or microgravity.

Comparative weights on bodies of the solar system

The following is a list of the weights of a mass on some of the bodies in the solar system, relative to its weight on Earth: For weight variations on Earth, see gee, physical geodesy and gravity anomaly.

Human weight in the medical sciences and ordinary language

Although many people prefer the less-ambiguous term body mass to body weight, the term weight is overwhelmingly used in daily English speech and in biological and medical science contexts. Body weight is measured in kilograms throughout the world. Most hospitals in the United States use kilograms for calculations, but use kilograms and pounds simultaneously for other purposes (a pound is 0.45 kg). Many people in the United Kingdom still measure their weight using the stone equal to 14 lb (6.35 kg).

Sports usage

Participants in sports such as boxing, wrestling, judo, and weight-lifting are classified according to their body weight, measured in units of mass such as pounds or kilograms. See, e.g., wrestling weight classes, boxing weight classes, judo at the 2004 Summer Olympics, boxing at the 2004 Summer Olympics. In horse racing, weight is used to handicap horses. A weight also refers to the physical objects used in weight-lifting and other sports such as the hammer throw.

Gee

:This article is about the unit of acceleration. GEE is also the name of a WWII radio navigation device built and implemented by the RAF for use in night bombing. For the Latin alphabet letter, see G. g (also gee, g-force or g-load) is a non-SI unit of acceleration defined as exactly 9.806 65 m/s², which is approximately equal to the acceleration due to gravity on the Earth's surface. The symbol g is properly written in lowercase and italic, to distinguish it from the symbol G, the gravitational constant, which is always written in uppercase and italic; and from g, the abbreviation for gram, which is not italicized. This conventional value was established by the 3rd CGPM (1901, CR 70). The total acceleration is found by vector addition of the opposite of the actual acceleration (in the sense of rate of change of velocity) and a vector of 1 g downward for the ordinary gravity (or in space, the gravity there). For example, being accelerated upward with an acceleration of 1 g doubles the experienced gravity. Conversely, weightlessness means an acceleration of 1 g downward in an inertial reference frame. The value of g defined above is an arbitrary midrange value on the Earth, approximately equal to the sea level acceleration of free fall at a geodetic latitude of about 45.5°; it is larger in magnitude than the average sea level acceleration on Earth, which is about 9.797 645 m/s². The standard acceleration of free fall is properly written as g_n (sometimes g₀) to distinguish it from the local value of g that varies with position. The units of acceleration due to gravity, meters per second squared, are interchangeable with newtons per kilogram. The quantity, 9.806 65, stays the same. These alternate units may be more helpful when considering problems involving pressure due to gravity, or weight.

Variations of Earth's gravity

The actual acceleration of a body at the Earth's surface depends on the location at which it is measured, smaller at lower latitudes, for two reasons. The first is that the rotation of the Earth imposes an additional acceleration on the body that opposes gravitational acceleration. The net downward force on the body is therefore offset by a centrifugal force that acts upwards, reducing its weight. This effect on its own would result in a range of values of g from 9.789 m/s² at the equator to 9.823 m/s² at the poles. The second reason is the Earth's equatorial bulge, which causes objects at the equator to be further from the planet's centre than objects at the poles. Because the force due to gravitational attraction between two bodies (the Earth and the object being weighed) varies inversely with the square of the distance between them, objects at the equator experience a weaker gravitational pull than objects at the poles. The combined result of these two effects is that g is 0.052 m/s² more, hence the force due to gravity of an object is 0.5% more, at the poles than at the equator. If the terrain is at sea level, we can estimate g, at a height h in the air above it: :

g_=9.780 327 \left( 1+0.0053024 ^2 \phi-0.0000058 ^2 2\phi \right)

where :

g_

= acceleration in m/s² at latitude φ This is the International Gravity Formula 1967, the 1967 Geodetic Reference System Formula, Helmert's equation or Clairault's formula. The first correction to this formula is the free air correction (FAC), which accounts for heights above sea level. Gravity decreases with height, at a rate which near the surface of the Earth is such that linear extrapolation would give zero gravity at a height of one half the radius of the Earth, i.e. the rate is 9.8 m/s² per 3200 km. Thus: :

g_=9.780 318 \left( 1+0.0053024 ^2 \phi-0.0000058 ^2 2\phi \right) - 3.086 \times 10^h

where :h = height in meters above sea level For flat terrain above sea level a second term is added, for the gravity due to the extra mass; for this purpose the extra mass can be approximated by an infinite horizontal slab, and we get 2πG times the mass per unit area, i.e. 4.2 × 10^-10 m³ s^-2 kg^-1 (0.000,042 mGal/(kg/m²)) (the Bouguer correction). For a mean rock density of 2.67 g/cm³ this gives 1.1 × 10^-6 s^-2 (0.11 mGal/m). Combined with the free-air correction this means a reduction of gravity at the surface of ca. 2 µm/s² (0.20 mGal) for every meter of elevation of the terrain. (The two effects would cancel at a surface rock density of 4/3 times the average density of the whole Earth.) For the gravity below the surface we have to apply the free-air correction as well as a double Bouguer correction. With the infinite slab model this is because moving the point of observation below the slab changes the gravity due to it to its opposite. Alternatively, we can consider a spherically symmetrical Earth and subtract from the mass of the Earth that of the shell outside the point of observation, because that does not cause gravity inside. This gives the same result. Local variations in both the terrain and the subsurface cause further variations; the gravitational geophysical methods are based on these: the small variations are measured, the effect of the topography and other known factors is subtracted, and from the resulting variations conclusions are drawn. See also physical geodesy and gravity anomaly.

Calculated value of g

Given the law of universal gravitation, g is merely a collection of factors in that equation: :

F = G \frac=(G \frac) m_2

where g is the bracketed factor and thus: :

g=G \frac

We can plug in values of

G

and the mass and radius of the Earth to obtain the calculated value of g: :

g=G \frac =(6.6742 \times 10^) \frac=9.822 \mbox^2

This agrees approximately with the measured value of g. The difference may be attributed to several factors:
- The Earth is not homogeneous
- The Earth is not a perfect sphere
- The choice of a value for the radius of the Earth (an average value is used above)
- The normal measured g also includes the centrifugal force effects due to the rotation of the Earth There are significant uncertainties in the values of G and of m₁ as used in this calculation. However, the value of g can be measured precisely and in fact, Henry Cavendish performed the reverse calculation to estimate the mass of the Earth.

Usage of the unit

The g is used primarily in aerospace fields, where it is a convenient magnitude when discussing the loads on aircraft and spacecraft (and their pilots or passengers). For instance, most civilian aircraft are capable of being stressed to 4.33 g (42.5 m/s²; 139 ft/s²), which is considered a safe value. The g is also used in automotive engineering, mainly in relation to cornering forces and collision analysis. One often hears the term being applied to the limits that the human body can withstand without losing conciousness, sometimes referred to as "blacking out", or g-loc (loc stands for loss of consciousness). A typical person can handle about 5 g (50 m/s²) before this occurs, but through the combination of special g-suits and efforts to strain muscles —both of which act to force blood back into the brain— modern pilots can typically handle 9 g (90 m/s²) sustained (for a period of time) or more. Resistance to "negative" or upward gees which drive blood to the head, is much less. This limit is typically in the -2 to -3 g (-20 to -30 m/s²) range. The vision goes red and is also referred to as a "red-out". This is probably due to capillaries in the eyes bursting under the increased blood pressure. Humans can survive about 20 to 40 g instantaneously (for a very short period of time), and any exposure to around 100 g instantaneous or more is lethal.

Human g-force experience

- Amusement park rides such as roller coasters typically do not expose the occupants to much more than about 2 g.
- A sky-diver in a stable free-fall experiences his full weight of 1 g. - (see terminal velocity)
- A scuba-diver experiences his full weight of 1 g.
- Astronauts in earth orbit experience 0 g.

Reference

International Association of Geodesy (1971) : Geodetic Reference System 1967. Publi. Spéc. n° 3 du Bulletin Géodésique, Paris. Category:Units of acceleration Category:Gravimetry ko:중력가속도 ja:重力加速度

Category:Statics

Category:Classical mechanics ko:분류:정역학

Category:Introductory physics

Category:Physics education

Bugi-vugi

A boogie woogie (magyarosan bugi-vugi) Egy zenei stílus neve. Gyökerei a country és a western muzsika mellett a blues, ami az 1940-es években lett igazán népszerű, és amit eleinte csak egy, később akár három zongora egyszerre, gitár vagy nagyzenekar (big band) játszott. Jellemzője a szabályos basszus kíséret (basso ostinato), melyet a bal kéz játszik, és a jobb kézzel játszott trillák és díszítések. Szigorúan véve nem szóló zongorastílus, szokták használni ének kíséreteként, illetve szólóként nagyzenekarban és kis jazz-együttesekben. Néha "eight to the bar"-nak (nyolc hang ütemenként) nevezik, de a legtöbb darab tulajdonképpen sima 4/4-es ütemű. Tipikus boogie woogie basszus Kép:Boogie-woogie-bassline.png A boogie woogie eredete bizonytalan, de az USA déli államainak kocsmáiban (honky tonk) játszott nyers zene hatása kétségtelen. W.C. Handy és Jelly Roll Morton is megemlítik, hogy néhány zongoristát már 1910 előtt is lehetett hallani ebben a stílusban játszani. Clarence Williams szerint a stílust elsőnek egy texasi zenész, George W. Thomas játszotta. Thomas 1916-ban publikálta az egyik legelső kottát ("New Orleans Hop Scop Blues") boogie woogie basszus kísérettel, bár azt Williams már 1911 előtt is hallotta tőle játszani. Jóllehet Clarence Williams az első zenészek egyike volt, aki 1923-ban boogie woogie lemezt vett fel, mégsem játszott tiszta boogie woogie stílust, inkább csak blues-kórusoknál a hangulat változtatására használta. A boogie woogie stílus minden bizonnyal széles körben elterjedt volt a fakitermelő táborokban éppúgy, mint minden egyéb munkahelyen, ahol nagy számban dolgoztak feketék, egészen az északi afro-amerikai közösségekig, mint pl. Chicago. Longhair professzor például szintén így indult, de stílusa nem különbözött annyira a korai kocsmazongorálástól. George W. Thomas szerzeményét, a The Fives-ot, melyet 1923 februárjában Joseph Samuels zenekara, a Tampa Blue Jazz Band vette lemezre az Okeh Records kiadónál tekintik az első hivatalos, nagyzenekar által játszott boogie woogie felvételnek. Az első teljes mértékben boogie woogie stílusú szóló darabnak Jimmy Blythe Chicago Stomps c. felvételét tekintik, 1924 áprilisából. A korai, tisztán boogie woogie felvételek közül kettő nagyon népszerű volt. Meade Lux Lewis szerzeményét, a "Honky Tonk Train Blues"-t 1927-ben rögzítették a Paramount Records-nál, majd 1930 márciusában adták ki. A "Pinetop's Boogie Woogie"-t, Clarence "Pinetop" Smith 1928-as felvételét 1929-ben adták ki, és ez volt az első boogie woogie sláger, ami hozzájárult a stílus névadásához. A boogie woogie 1937/38-ban kapott nagy nyilvánosságot, amikor John Hammond a Carnegie Hallban From Spirituals to Swing címmel koncerteket hirdetett. Ezeken többek között elhangzott Pete Johnson és Big Joe Turner előadásában a "Turner's tribute to Johnson" és "Roll 'Em, Pete", Meade Lux Lewis által a "Honky Tonk Train Blues" és Albert Ammons "Swanee River Rock"-ja is. (a "Roll 'Em, Pete" egyike az első rock and roll felvételeknek) Ez a három zongorista Turnerrel a New York City-beli Café Society night clubban ütötték fel rezidenciájukat, ahol a kifinomult társaság szerette őket. Gyakran játszottak párban, sőt egyszerre hárman, gazdagon előadott zongorajátékot alkotva. Népszerűségük nagy hatással volt a kortárs boogie woogie zongoristákra és arra, hogy a boogie woogie hangzást sok más zenei irányzat is adaptálta. Nem sokkal Tommy Dorsey bandája "T.D.'s Boogie Woogie" c. nótája után egy csomó, különböző vonalat képviselő boogie woogie zenész jelent meg. Conlon Nancarrow zeneszerző is mélyen a boogie woogie hatása alá került, ahogy azt zongorára írt korai munkáinak nagy része is mutatja. Annak ellenére, hogy csak néhány évig tartott, a boogie woogie hóbort volt az egyik legnagyobb hatással a jump-blues és végeredményben a rock and roll fejlődésére, mind a mai napig hallani különböző klubokban, lemezeken szerte Európában és az Egyesült Államokban. Kategória:Zenei stílusok

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