Horizontal plane - Citizendia

In astronomy, geography, geometry and related sciences and contexts, a plane is said to be horizontal at a given point if it is locally perpendicular to the gradient of the gravity field, i. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands features inhabitants and phenomena Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position In Vector calculus, the gradient of a Scalar field is a Vector field which points in the direction of the greatest rate of increase of the scalar Gravitation is a natural Phenomenon by which objects with Mass attract one another In Physics, a field is a Physical quantity associated to each point of Spacetime. e. , with the direction of the gravitational force (per unit mass) at that point.

In radio science, horizontal plane is used to plot an antenna's relative field strength (which directly affects a station's coverage area) on a polar graph. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into In Physics, the field strength of a field is the magnitude of its vector value In Mathematics, the polar coordinate system is a two-dimensional Coordinate system in which each point on a plane is determined by Normally the maximum of 1. 000 or 0 dB is at the top, which is labeled 0^o, running clockwise back around to the top at 360°. The decibel ( dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity relative to Other field strengths are expressed as a decimal less than 1. 000, a percentage less than 100%, or decibels less than 0 dB. If the graph is of an actual or proposed installation, rotation is applied so that the top is 0^o true north. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation noted by the Chinese Polymath Shen Kuo in the 11th century and possibly the egyptians over 6 millenia ago See also the perpendicular vertical plane. Vertical plane is used in radio to plot an antenna's relative Field strength perpendicular to the ground (which directly affects a station's coverage area on a polar graph

Discussion

Although the word horizontal is very commonly used in daily life and language (see below), it is subject to many misconceptions. The precise definition above and the following discussion points will hopefully clarify these issues.

The concept of horizontality only makes sense in the context of a clearly measurable gravity field, i. e. , in the 'neighborhood' of a planet, star, etc. When the gravity field becomes very weak (the masses are too small or too distant from the point of interest), the notion of being horizontal loses its meaning.

In the presence of a simple, time-invariant, rotationally symmetric gravity field, a plane is horizontal only at the reference point. The horizontal planes with respect to two separate points are not parallel, they intersect.

In general, a horizontal plane will only be perpendicular to a vertical direction if both are specifically defined with respect to the same point: a direction is only vertical at the point of reference. In Astronomy, Geography, Geometry and related sciences and contexts a direction passing by a given point is said to be vertical if Thus both horizontality and verticality are strictly speaking local concepts, and it is always necessary to state to which location the direction or the plane refers to. Note that (1) the same restriction applies to the straight lines contained within the plane: they are horizontal only at the point of reference, and (2) those straight lines contained in the plane but not passing by the reference point are not horizontal anywhere.

In reality, the gravity field of a heterogeneous planet such as Earth is deformed due to the inhomogeneous spatial distribution of materials with different densities. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Actual horizontal planes are thus not even parallel even if their reference points are along the same vertical direction.

At any given location, the total gravitational force is a function of time, because the objects that generate the reference gravity field move relative to each other. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of For instance, on Earth, the local horizontal plane at a given point (as materialized by a pair of spirit levels) changes with the relative position of the Moon (air, sea and land tides). A spirit level or bubble level is an instrument designed to indicate whether a surface is Level or Plumb. Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood

Furthermore, on a rotating planet such as Earth, there is a difference between the strictly gravitational pull of the planet (and possibly other celestial objects such as the Moon, the Sun, etc), and the apparent net force applied (e. The Sun (Sol is the Star at the center of the Solar System. g. , on a free-falling object) that can be measured in the laboratory or in the field. This difference is due to the centrifugal force associated with the planet's rotation. This is a fictitious force: it only arises when calculations or experiments are conducted in non-inertial frames of reference. A fictitious force, also called a pseudo force, d'Alembert force or inertial force, is an apparent Force that acts on all masses in a non-inertial In Physics, an inertial frame of reference is a Frame of reference which belongs to a set of frames in which Physical laws hold in the same and simplest

Practical use in daily life

The concept of a horizontal plane is thus anything but simple, although, in practice, most of these effects and variations are rather small: they are measurable and can be predicted with great accuracy, but they may not greatly affect our daily life.

This dichotomy between the apparent simplicity of a concept and an actual complexity of defining (and measuring) it in scientific terms arises from the fact that the typical linear scales and dimensions of relevance in daily life are 3 orders of magnitude (or more) smaller than the size of the Earth. An order of magnitude is the class of scale or magnitude of any amount where each class contains values of a fixed ratio to the class preceding it Hence, the latter appears to be flat locally, and horizontal planes in nearby locations appear to be parallel. Such statements are nevertheless approximations; whether they are acceptable in any particular context or application depends on the applicable requirements, in particular in terms of accuracy.

In graphical contexts, such as drawing and drafting on rectangular paper, it is very common to associate one of the dimensions of the paper with a horizontal, even though the entire sheet of paper is standing on a flat horizontal (or slanted) table. In this case, the horizontal direction is typically from the left side of the paper to the right side. This is purely conventional (although it is somehow 'natural' when drawing a natural scene as it is seen in reality), and may lead to misunderstandings or misconceptions, especially in an educational context.