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# 7 fundamental quantities and their units

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Fundamental unit - Wikipedia, the free encyclopedia

In the SI system there are 7 fundamental units: kilogram, meter, candela, ... have cast doubt on the very existence of incompatible fundamental quantities. ...

Units of energy

Because energy is defined via work, the SI unit for energy is the same as the unit of work &ndash; the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1&nbsp;joule is equal to 1&nbsp;newton-metre and, in terms of SI base units:

1\ \mathrm{J} = 1\ \mathrm{kg} \left( \frac{\mathrm{m}}{\mathrm{s}} \right ) ^ 2 = 1\ \frac{\mathrm{kg} \cdot \mathrm{m}^2}{\mathrm{s}^2}

An energy unit that is used in atomic physics, particle physics and high energy physics is the electronvolt (eV). One&nbsp;eV&nbsp; is equivalent to 1.60217653&times;10&minus;19&nbsp;J. In spectroscopy the unit cmâˆ’1 = 0.0001239 eV is used to represent energy since energy is inversely proportional to wavelength from the equation E = h \nu = h c/\lambda .

In discussions of energy production and consumption, the units barrel of oil equivalent and ton of oil equivalent are often used.

When discussing amounts of energy released in explosions or bolideimpact events, the TNT equivalent unit is often used. 1 ton of TNT equivalent is equal to 4.2 &times; 109 joules. Therefore, 1 kt TNT is 4.2 &times; 1012 joules, and 1 Mt TNT is 4.2 &times; 1015 joules.

Note that torque, the "rotational force" or "angular force" which causes a change in rotational motion is typically expressed in newton-metres. This is not a simple coincidence: a torque of 1 newton-metre applied on 1 radian requires exactly 1 newton-metre = 1 joule of energy.

## Other units of energy

In cgs units, one erg is 1&nbsp;g&nbsp;cm2&nbsp;s&minus;2, equal to 1.0&times;10&minus;7&nbsp;J.

The imperial/U.S. units for both energy and work include the foot-pound force (1.3558&nbsp;J), the British thermal unit (Btu) which has various values in the region of 1055 J, and the horsepower-hour (2.6845 MJ).

The energy unit used for everyday electricity, particularly for utility bills, is the kilowatt-hour (kWh), and one kWh is equivalent to 3.6&times;106&nbsp;J&nbsp; (3600&nbsp;kJ or 3.6&nbsp;MJ). Electricity usage is often given in units of kilowatt-hours per year (kWh/yr). This is actually a measurement of average power consumption, i.e., the average rate at which energy is transferred.

The calorie equals the amount of thermal energy necessary to raise the temperature of one gram of water by 1 Celsius degree, at a pressure of 1 atm. For thermochemistry a calorie of 4.184 J is used, but other calories have also been defined, such as the International Steam Table calorie of 4.1868 J. Food energy is measured in large calories or kilocalories, often simply written capitalized as "Calories" (= 103 calories).

In physics and chemistry, it is still common to measure energy on the atomic scale in the non-SI, but convenient, units electronvolts (eV). The Hartree (the atomic unit of energy) is commonly used in calculations. Historically Rydberg units have been used.

In spectroscopy and related fields it is common to measure energy levels in units of reciprocal centimetres. These units (cmâˆ’1) are strictly speaking not energy units but units proportional to energies, with hc being the proportionality constant.

## Conversion of units

For conversion of units of energy, see energy unit conversion.

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Unit of time

Units of measurement for time have historically been based on the movement of the Sun (as seen from Earth; giving the solar day and the year) and the Moon (giving the month). Shorter intervals were measured by physiological periods such as drawing breath, winking or the heartbeat.

Units of time consisting of a number of years include the lustrum (five years) and the olympiad (four years). The month could be divided into half-months or fortnights, and quarters or weeks. Longer periods were given in lifetimes or generations (saecula, aion), subdivisions of the solar day in hours. The Sothic cycle was a period of 1,461 years of 365 days in the Ancient Egyptian calendar. Medieval (Pauranic) Hindu cosmologyÂ is notorious for introducing names for fabulously long time periods, such as kalpaÂ (4.32 billion years).

In classical antiquity, the hour divided the daylight period into 12 equal parts. The duration of an hour thus varied over the course of the year. In classical China, the kÃ¨(åˆ») was a unit ofdecimal time, dividing a day into 100 equal intervals of 14.4 minutes. Alongside the ke, there were double hours (shÃ­chen) also known as watches. Because one cannot divide 12 double hours into 100 ke evenly, each ke was subdivided into 60 fÄ“n (åˆ†).

The introduction of the minute (minuta; â€²) as the 60th part of an hour, the second (seccunda; â€²â€²) as the 60th part of a minute, and the third (tertia; â€²â€²â€²) as the 60th part of the second dates to the medieval period, used by Al-Biruni around AD 1000, and by Roger Bacon in the 13th century. Bacon further subdivided the tertia into a quarta or fourth (â€²â€²â€²â€²). Hindu chronologyÂ divides the civil day (daylight hours) into vipalas, palas and ghatikas. A tithiis the 30th part of thesynodic month.

The introduction of the division of the solar day into 24 hours of equal length, as it were the length of a classical hour at equinox used regardless of daylight hours, dates to the 14th century, due to the development of the first mechanical clocks.

Today, the fundamental unit of time suggested by the International System of Units is the second, since 1967 defined as the second of International Atomic Time, based on the radiation emitted by a Caesium-133 atom in the ground state. Its definition is still so calibrated that 86,400 seconds correspond to a solar day. 31,557,600 (86,400 Ã— 365.25) seconds are a Julian year, exceeding the true length of a solar year by about 21 ppm.

Based on the second as the base unit, the following time units are in use:

There are a number of proposals for decimal time, or decimal calendars, notably in the French Republican Calendar of 1793. Such systems have either ten days per week, a multiple of ten days in a month, or ten months per year.

A suggestion for hexadecimal time divides the Julian day into 16 hexadecimal hours of 1h 30 min each, or 65,536 hexadecimal seconds (1 hexsec â‰ˆ 1.32 s).

The Planck time (tP) is a natural unit of time, the shortest possible interval that can be meaningfully considered inquantum mechanics. tPequals about 5.4&nbsp;Ã—&nbsp;10&minus;44&nbsp;s.

Question:

Answers:Length- Meter (m) Mass- Kilogram (kg) Time- Second (s) Electric current- Ampere (A) Temperature- Kelvin (K) Luminous intensity- Candela (cd) Amount of substance- Mole (mol)

Question:please help me....because of this question my first day of school got to be very embarrass...i couldn't even answer this question and my teacher gave this to me as my homework...huhuhuhuhuhuhu T^T thank you for those people who will answer this question...mwah!!

Answers:Here are the seven fundamental quantities. I also included their definitions and SI units. length - meter (m) - the measurement or extent of something from end to end. mass - kilogram (kg) - a coherent body of matter with no definite shape. time - second (s) - the indefinite continued progress of existence and events. electric current - ampere (A) - flow of electric charge. thermodynamic temperature - kelvin (K) - A measure proportional to the thermal energy of a given body at equilibrium. amount of substance - mole (mol) - the number of specified group of entities present in a substance. luminous intensity - candela (cd) - an expression of the amount of light power emanating from a point source within a solid angle of one steradian.

Question:can any one list out the 7 fundamental Qs 4me, thanx...

Answers:(I)fundamental units: those units which are the quantities which are independent of each other. All other quantities may be expressed in these units. It turns out that the number of fundamental units is 7. They are: (a)length (metre; m) (b)mass (kilogram, kg) (c)time (second, s) (d)luminous intensity (candela, cd) (e)electric intensity (ampere, A) (f)amount of substance (mole, mol) (g)thermodynamic temperature (Kelvin, K)

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