add units

science/physics/SI Units.md

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 | zetta  | `Z`    | $10^{21}$  |
 
 ## Derived Units
+#refactor #notnow -> add more units
 ### Electricity
 - [Volt](units/Volt.md)

science/physics/units/Ampere.md

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+---
+obj: science/unit
+---
+
+# Ampere
+The ampere (symbol: A) is the SI base unit of electric current. It is a fundamental quantity in electromagnetism and plays a crucial role in understanding and quantifying the flow of electric charge through conductors.
+
+## History
+The ampere is named after André-Marie Ampère, a French physicist and mathematician who made significant contributions to the study of electromagnetism in the 19th century. The concept of electric current existed before Ampère's work, but his experiments and theories helped establish the modern understanding of current and its measurement.
+
+## Definition
+The ampere is defined as the constant current that, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in a vacuum, would produce between these conductors a force equal to $2 × 10^{-7}$ newtons per [meter](Meter.md) of length. This definition, known as Ampère's force law, provides a precise and standardized basis for measuring electric current.
+
+## Practical Applications
+- **Electrical Engineering:** The ampere is used in electrical engineering to specify the current rating of electrical components such as wires, cables, and circuit breakers. It is also essential for designing electrical circuits and systems.
+- **Electronics:** In electronics, the ampere is used to measure the current flowing through electronic devices such as transistors, diodes, and integrated circuits.
+- **Power Generation and Distribution:** Ampere measurements are crucial for monitoring and controlling the flow of electric current in power generation and distribution systems, including power plants, substations, and electrical grids.
+- **Electric Motors and Machinery:** The ampere is used to characterize the current drawn by electric motors and other machinery, providing information about their power consumption and performance.

science/physics/units/Candela.md

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+obj: science/unit
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+
+# Candela
+The candela (symbol: cd) is the SI base unit of luminous intensity. It is defined as the luminous intensity in a given direction of a source that emits monochromatic radiation with a frequency of 540 terahertz (THz) and has a radiant intensity in that direction of $\frac{1}{683}$ watt per steradian. In simpler terms, the candela measures how much light is emitted in a particular direction.

science/physics/units/Kelvin.md

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+---
+obj: science/unit
+---
+
+# Kelvin
+The kelvin (symbol: K) is the SI base unit of temperature. It is commonly used in scientific and engineering contexts, particularly in disciplines such as [physics](../Physics.md), [chemistry](../../chemistry/Chemistry.md), and materials science. The kelvin scale is based on absolute zero, the theoretical lowest possible temperature, and provides a precise and universally applicable way to measure temperature.
+
+## History
+The kelvin scale was established in the 19th century by the Scottish physicist William Thomson, 1st Baron Kelvin, who proposed a temperature scale with absolute zero as its starting point. In 1954, the 10th General Conference on Weights and Measures (CGPM) officially adopted the kelvin as one of the base units of the International System of Units (SI).
+
+## Definition
+The kelvin is defined as $\frac{1}{273.16}$ of the thermodynamic temperature of the triple point of water. The triple point of water is the unique combination of temperature and pressure at which water can coexist in equilibrium as a solid, liquid, and gas. This definition ensures that the kelvin scale is tied to fundamental properties of matter and is independent of the properties of any specific substance.
+
+## Practical Applications
+- **Scientific Research:** The kelvin scale is used in scientific research to measure temperatures in a wide range of fields, including physics, chemistry, astronomy, and environmental science.
+- **Engineering:** Engineers use the kelvin scale to design and test various systems and devices that involve temperature control, such as heating and cooling systems, engines, and electronic components.
+- **Materials Science:** Temperature plays a crucial role in the properties and behavior of materials. The kelvin scale is essential in materials science for studying phase transitions, thermal expansion, and other temperature-dependent phenomena.
+- **Meteorology:** While the Celsius and Fahrenheit scales are more commonly used for everyday weather reporting, the kelvin scale is used in meteorology for scientific research and in specialized applications such as climate modeling.
+
+## Symbol and Usage
+The symbol for the kelvin is "K." Temperatures measured in kelvin are typically expressed without the degree symbol (°). For example, the freezing point of water is 273.15 K.

science/physics/units/Kilogram.md

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+obj: science/unit
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+# Kilogram
+The kilogram (symbol: kg) is the SI base unit of mass. It is used as a fundamental measurement of mass in various fields, including [physics](../Physics.md), engineering, [chemistry](../../chemistry/Chemistry.md), and everyday life. The kilogram serves as a reference for measuring the mass of objects and substances.
+
+## History
+The kilogram has a long history, with its modern definition evolving over time. The International Prototype of the Kilogram (IPK), a physical object made of platinum-iridium alloy, served as the primary standard for the kilogram since it was established in 1889. However, efforts to redefine the kilogram in terms of fundamental constants led to a new definition in 2019 based on the Planck constant.
+
+## Definition
+The kilogram is currently defined as the mass of the International Prototype of the Kilogram (IPK), which is a platinum-iridium cylinder stored at the International Bureau of Weights and Measures (BIPM) in France. However, as of 2019, the kilogram is officially defined in terms of the Planck constant (h), a fundamental constant of nature, as part of the redefinition of the International System of Units (SI).
+
+## Practical Applications
+- **Measurement:** The kilogram is used to measure the mass of various objects and substances in laboratories, industries, and everyday life.
+- **Commerce:** Mass measurements are crucial in commerce for trading goods, determining quantities, and ensuring product quality and consistency.
+- **Engineering:** The kilogram is used in engineering for designing and manufacturing products, calculating forces and loads, and specifying material properties.
+- **Healthcare:** In healthcare, the kilogram is used for measuring body weight, dosage of medications, and other medical parameters.

science/physics/units/Meter.md

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+---
+obj: science/unit
+---
+
+# Meter
+The meter (symbol: m) is the SI base unit of length. It is widely used for measuring distances, dimensions, and quantities in various fields, including [physics](../Physics.md), engineering, construction, and everyday life. The meter provides a standardized and universally accepted way to quantify length.
+
+## History
+The meter has a long history, with its modern definition evolving over time. Originally, the meter was defined as one ten-millionth of the distance from the equator to the North Pole along a meridian passing through Paris. In 1983, the meter was redefined in terms of the speed of light in a vacuum, providing a more precise and universal definition.
+
+## Definition
+The meter is currently defined as the distance that light travels in a vacuum in $\frac{1}{299,792,458}$ seconds. This definition, based on the speed of light, ensures that the meter is consistent and reproducible across different measurement systems and technologies.
+
+## Practical Applications
+- **Measurement:** The meter is used for measuring distances, lengths, heights, widths, and other dimensions in various applications, from scientific research to everyday activities.
+- **Construction:** In construction and civil engineering, the meter is used for planning, designing, and building structures, roads, and infrastructure.
+- **Navigation:** The meter is essential for navigation and cartography, providing a standard unit for measuring distances on maps, charts, and GPS devices.
+- **Manufacturing:** In manufacturing and industry, the meter is used for specifying product dimensions, tolerances, and quality standards.

science/physics/units/Mole.md

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+obj: science/unit
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+
+# Mole
+The mole (symbol: mol) is the SI base unit for amount of substance. It provides a way to measure the quantity of entities, such as atoms, molecules, ions, or other specified particles, in a sample of a substance. The mole is essential in [chemistry](../../chemistry/Chemistry.md) and related fields for quantifying chemical reactions, stoichiometry, and other fundamental concepts.
+
+## History
+The concept of the mole dates back to the late 19th century, but its formal definition was established in the 1960s by the International Union of Pure and Applied Chemistry (IUPAC). This definition was refined over time to its current form.
+
+## Definition
+The mole is defined as the amount of substance that contains exactly $6.02214076 × 10^{23}$ specified elementary entities. These entities may be atoms, molecules, ions, or other particles, depending on the context of the substance being measured. This number is known as Avogadro's number, named after the Italian scientist Amedeo Avogadro, who first proposed the concept in the early 19th century.
+
+## Practical Applications
+- **Chemical Reactions:** The mole allows chemists to express the amounts of reactants and products in a chemical reaction, facilitating stoichiometric calculations.
+- **Formulation of Solutions:** The mole is used to measure the quantities of solutes and solvents in solutions, enabling accurate preparation of solutions with desired concentrations.
+- **Analysis and Synthesis:** In analytical chemistry, the mole is used to quantify the amounts of substances present in a sample, while in synthetic chemistry, it guides the synthesis of specific compounds by determining the required amounts of reactants.
+- **Industrial Processes:** The mole is crucial in industrial processes such as manufacturing, where precise amounts of chemicals are needed to produce desired products efficiently and economically.

science/physics/units/Second.md

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+obj: science/unit
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+
+# Second
+The second (symbol: s) is the SI base unit of time. It is a fundamental unit of measurement in [physics](../Physics.md), engineering, astronomy, and various other fields, providing a standardized and universally accepted way to quantify time intervals.
+
+## History
+The division of the day into hours, minutes, and seconds has been used since ancient times, but the modern concept of the second as a standardized unit of time emerged in the late 16th century. In 1960, the 11th General Conference on Weights and Measures (CGPM) officially defined the second as the duration of $9,192,631,770$ periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.
+
+## Definition
+The second is defined based on the behavior of cesium atoms in atomic clocks, which are highly accurate timekeeping devices. Specifically, it is defined as the duration of $9,192,631,770$ periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom at rest and at a temperature of 0 [Kelvin](Kelvin.md).
+
+## Practical Applications
+- **Timekeeping:** The second is used as the basis for measuring time intervals in clocks, watches, and other timekeeping devices, from everyday clocks to highly precise atomic clocks used in scientific research and navigation systems.
+- **Navigation:** In GPS (Global Positioning System) and other satellite-based navigation systems, precise timing based on atomic clocks is essential for determining positions accurately.
+- **Communications:** The second is crucial for synchronizing communication networks, such as telecommunications and the internet, ensuring accurate transmission and coordination of data.
+- **Scientific Research:** The second is used in various scientific experiments and observations to measure durations, frequencies, and rates of change in physical phenomena.