A typical tape measure with both metric and US units and two US pennies for comparison

Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the meter, second or degree Celsius. The science of measurement is called metrology.

The English word measurement originates from the Latin mēnsūra and the verb metiri through the Middle French mesure.^[1]

Standards[link]

With the exception of a few seemingly fundamental quantum constants, units of measurement are essentially arbitrary; in other words, people make them up and then agree to use them. Nothing inherent in nature dictates that an inch has to be a certain length, or that a mile is a better measure of distance than a kilometre. Over the course of human history, however, first for convenience and then for necessity, standards of measurement evolved so that communities would have certain common benchmarks. Laws regulating measurement were originally developed to prevent fraud in commerce.

Today, units of measurement are generally defined on a scientific basis, overseen by governmental or supra-governmental agencies, and established in international treaties, pre-eminent of which is the General Conference on Weights and Measures (CGPM), established in 1875 by the Treaty of the metre and which oversees the International System of Units (SI) and which has custody of the International Prototype Kilogram. The metre, for example, was redefined in 1983 by the CGPM as the distance traveled by light in free space in 1⁄299,792,458 of a second while in 1960 the international yard was defined by the governments of the United States, United Kingdom, Australia and South Africa as being exactly 0.9144 metres.

In the United States, the National Institute of Standards and Technology (NIST), a division of the United States Department of Commerce, regulates commercial measurements. In the United Kingdom, the role is performed by the National Physical Laboratory (NPL), in Australia by the Commonwealth Scientific and Industrial Research Organisation, in South Africa by the Council for Scientific and Industrial Research and in India the National Physical Laboratory of India.

Units and systems[link]

Four measuring devices having metric calibrations

Imperial system[link]

Before SI units were widely adopted around the world, the British systems of English units and later imperial units were used in Britain, the Commonwealth and the United States. The system came to be known as U.S. customary units in the United States and is still in use there and in a few Caribbean countries. These various systems of measurement have at times been called foot-pound-second systems after the Imperial units for length, weight and time even though the tons, hundredweights, gallons, and nautical miles, for example, are different for the U.S. units. Many Imperial units remain in use in Britain which has officially partially switched to the SI system. Road signs are still in miles, yards, miles per hour; milk, beer and cider are sold by the pint; people measure their height in feet and inches and their weight in stone and pounds, to give just a few examples. Imperial units are used in many other places, for example, in many Commonwealth countries that are considered metricated, land area is measured in acres and floor space in square feet, particularly for commercial transactions (rather than government statistics). Similarly, gasoline is sold by the gallon in many countries that are considered metricated.

Metric system[link]

The metric system is a decimal systems of measurement based on its units for length, the metre and for mass, the kilogram. It exists in several variations, with different choices of base units, though these do not affect its day-to-day use. Since the 1960s, the International System of Units (SI) is the internationally recognized metric system. Metric units of mass, length, and electricity are widely used around the world for both everyday and scientific purposes.

The metric system features a single base unit for many physical quantities. Other quantities are derived from the standard SI units. Multiples and fractions of the units are expressed as Powers of 10 of each unit. Unit conversions are always simple because they are in the ratio of ten, one hundred, one thousand, etc., so that convenient magnitudes for measurements are achieved by simply moving the decimal place: 1.234 metres is 1234 millimetres or 0.001234 kilometres. The use of fractions, such as 2/5 of a metre, is not prohibited, but uncommon. All lengths and distances, for example, are measured in metres, or thousandths of a metre (millimetres), or thousands of metres (kilometres). There is no profusion of different units with different conversion factors as in the Imperial system which uses, for example, inches, feet, yards, fathoms, rods.

International System of Units[link]

The International System of Units (abbreviated as SI from the French language name Système International d'Unités) is the modern revision of the metric system. It is the world's most widely used system of units, both in everyday commerce and in science. The SI was developed in 1960 from the metre-kilogram-second (MKS) system, rather than the centimetre-gram-second (CGS) system, which, in turn, had many variants. During its development the SI also introduced several newly named units that were previously not a part of the metric system. The original SI units for the six basic physical quantities were:^[2]

• metre (m)  :SI unit of length
• second (s)  :SI unit of time
• kilogram (kg)  :SI unit of mass
• ampere (A)  :SI unit of electric current
• degree kelvin (K) :SI unit of thermodynamic temperature
• candela (cd)  :SI unit of luminous intensity

The mole was subsequently added to this list and the degree Kelvin renamed the kelvin.

There are two types of SI units, base units and derived units. Base units are the simple measurements for time, length, mass, temperature, amount of substance, electric current and light intensity. Derived units are constructed from the base units, for example, the watt, i.e. the unit for power, is defined from the base units as m²·kg·s⁻³. Other physical properties may be measured in compound units, such as material density, measured in kg/m³.

Converting prefixes[link]

The SI allows easy multiplication when switching among units having the same base but different prefixes. To convert from metres to centimetres it is only necessary to multiply the number of metres by 100, since there are 100 centimetres in a metre. Inversely, to switch from centimetres to metres one multiplies the number of centimetres by 0.01 or divide centimetres by 100.

Length[link]

A 2-metre carpenter's ruler

A ruler or rule is a tool used in, for example, geometry, technical drawing, engineering, and carpentry, to measure lengths or distances or to draw straight lines. Strictly speaking, the ruler is the instrument used to rule straight lines and the calibrated instrument used for determining length is called a measure, however common usage calls both instruments rulers and the special name straightedge is used for an unmarked rule. The use of the word measure, in the sense of a measuring instrument, only survives in the phrase tape measure, an instrument that can be used to measure but cannot be used to draw straight lines. As can be seen in the photographs on this page, a two-metre carpenter's rule can be folded down to a length of only 20 centimetres, to easily fit in a pocket, and a five-metre-long tape measure easily retracts to fit within a small housing.

Some special names[link]

We also use some special names for some multiples of some units.

• 100 kilograms = 1 quintal; 1000 kilogram = 1 metric tonne;
• 10 years = 1 decade; 100 years = 1 century; 1000 years = 1 millennium

Building trades[link]

The Australian building trades adopted the metric system in 1966 and the units used for measurement of length are metres (m) and millimetres (mm). Centimetres (cm) are avoided as they cause confusion when reading plans. For example, the length two and a half metres is usually recorded as 2500 mm or 2.5 m; it would be considered non-standard to record this length as 250 cm.

Surveyor's Trade[link]

American surveyors use a decimal-based system of measurement devised by Edmund Gunter in 1620. The base unit is Gunter's chain of 66 feet (20 m) which is subdivided into 4 rods, each of 16.5 ft or 100 links of 0.66 feet. A link is abbreviated "lk," and links "lks" in old deeds and Land Surveys done for the government.

Time[link]

Time is an abstract measurement we have invented in order to keep track of elemental changes over a non spatial continuum. It is denoted by numbers and/or named periods such as hours, days, weeks, months and years. It is an apparently irreversible series of occurrences within this non spatial continuum. It is also used to denote an interval between two relative points on this continuum.

Mass[link]

Mass refers to the intrinsic property of all material objects to resist changes in their momentum. Weight, on the other hand, refers to the downward force produced when a mass is in a gravitational field. In free fall, (no net gravitational forces) objects lack weight but retain their mass. The Imperial units of mass include the ounce, pound, and ton. The metric units gram and kilogram are units of mass.

One device for measuring weight or mass is called a weighing scale or, often, simply a scale. A spring scale measures force but not mass, a balance compares weight, both require a gravitational field to operate. Some of the most accurate instruments for measuring weight or mass are based on load cells with a digital read-out, but require a gravitational field to function and would not work in free fall.

Economics[link]

The measures used in economics are physical measures, nominal price value measures and fixed price value measures. These measures differ from one another by the variables they measure and by the variables excluded from measurements. The measurable variables in economics are quantity, quality and distribution. By excluding variables from measurement makes it possible to better focus the measurement on a given variable, yet, this means a narrower approach.

Difficulties[link]

Since accurate measurement is essential in many fields, and since all measurements are necessarily approximations, a great deal of effort must be taken to make measurements as accurate as possible. For example, consider the problem of measuring the time it takes an object to fall a distance of one metre (about 39 in). Using physics, it can be shown that, in the gravitational field of the Earth, it should take any object about 0.45 second to fall one metre. However, the following are just some of the sources of error that arise:

1. This computation used for the acceleration of gravity 9.8 metres per second squared (32 ft/s²). But this measurement is not exact, but only precise to two significant digits.
2. The Earth's gravitational field varies slightly depending on height above sea level and other factors.
3. The computation of .45 seconds involved extracting a square root, a mathematical operation that required rounding off to some number of significant digits, in this case two significant digits.

So far, we have only considered scientific sources of error. In actual practice, dropping an object from a height of a metre stick and using a stopwatch to time its fall, we have other sources of error:

1. Most common, is simple carelessness.
2. Determining the exact time at which the object is released and the exact time it hits the ground. There is also the problem that the measurement of the height and the measurement of the time both involve some error.
3. Air resistance

Scientific experiments must be carried out with great care to eliminate as much error as possible, and to keep error estimates realistic.

Definitions and theories[link]

Classical definition[link]

In the classical definition, which is standard throughout the physical sciences, measurement is the determination or estimation of ratios of quantities.^[3] Quantity and measurement are mutually defined: quantitative attributes are those possible to measure, at least in principle. The classical concept of quantity can be traced back to John Wallis and Isaac Newton, and was foreshadowed in Euclid's Elements.^[4]

Representational theory[link]

In the representational theory, measurement is defined as "the correlation of numbers with entities that are not numbers".^[5] The most technically elaborate form of representational theory is also known as additive conjoint measurement. In this form of representational theory, numbers are assigned based on correspondences or similarities between the structure of number systems and the structure of qualitative systems. A property is quantitative if such structural similarities can be established. In weaker forms of representational theory, such as that implicit within the work of Stanley Smith Stevens,^[6] numbers need only be assigned according to a rule.

The concept of measurement is often misunderstood as merely the assignment of a value, but it is possible to assign a value in a way that is not a measurement in terms of the requirements of additive conjoint measurement. One may assign a value to a person's height, but unless it can be established that there is a correlation between measurements of height and empirical relations, it is not a measurement according to additive conjoint measurement theory. Likewise, computing and assigning arbitrary values, like the "book value" of an asset in accounting, is not a measurement because it does not satisfy the necessary criteria.

Information theory[link]

Information theory recognizes that all data are inexact and statistical in nature. Thus the definition of measurement is: "A set of observations that reduce uncertainty where the result is expressed as a quantity."^[7] This definition is implied in what scientists actually do when they measure something and report both the mean and statistics of the measurements. In practical terms, one begins with an initial guess as to the value of a quantity, and then, using various methods and instruments, reduces the uncertainty in the value. Note that in this view, unlike the positivist representational theory, all measurements are uncertain, so instead of assigning one value, a range of values is assigned to a measurement. This also implies that there is not a clear or neat distinction between estimation and measurement. Ascertaining the degree measurement error is also a basic facet of metrology, and sources of errors are divided into systematic and non-systematic.

Quantum mechanics[link]

In quantum mechanics, a measurement is an action that determines the location of an object, its momentum, its polarity (if it is a photon), etc. Before a measurement is made, the wavefunction of what is to be measured gives the range of probabilities for the outcomes of measurement, but when a measurement is accomplished that results in what is called the collapse of the wavefunction− at which time there is one definite value rather than a range of possible values.^{[citation needed]} The unambiguous meaning of the measurement problem is an unresolved fundamental problem in quantum mechanics.^{[citation needed]}

See also[link]

References[link]

External links[link]

Look up measurement in Wiktionary, the free dictionary.

• BIPM International Vocabulary of Measurement (VIM)
• 'Universcale', an application showing the relative sizes of objects
• A Dictionary of Units of Measurement
• Comprehensive Unit Conversion Calculator
• 'Metrology – in short' 3rd edition, July 2008 ISBN 978-87-988154-5-7
• mensuration formulas A collection of important mensuration formulas.

Bill Nye
Nye at Bridgewater State University in 2007
Born	(1955-11-27) November 27, 1955 (age 56)[1] Washington, D.C.[1]
Residence	Los Angeles
Fields	Mechanical engineering
Institutions	Boeing Cornell University Planetary Society
Alma mater	Cornell University (BS)
Known for	Bill Nye the Science Guy
Signature

William Sanford "Bill" Nye (born November 27, 1955),^[2] popularly known as Bill Nye the Science Guy, is an American science educator, comedian, television host, actor, mechanical engineer, and scientist. He is best known as the host of the Disney/PBS children's science show Bill Nye the Science Guy (1993–1998) and for his many subsequent appearances in popular media as a science educator.

Early life and career[link]

William Sanford Nye was born in Washington, D.C., the son of Jacqueline (née Jenkins; c. 1920–2000), a codebreaker during World War II, and Edwin Darby "Ned" Nye (died 1997), also a World War II veteran whose experience in a Japanese prisoner of war camp led him to become a sundial enthusiast.^[3][4][5] Nye is a fourth-generation Washington, D.C. resident on his father's side of the family. After attending Lafayette Elementary and Alice Deal Junior High in the city, he was accepted to the private Sidwell Friends School on a partial scholarship, graduating in 1973.^[6][7] He studied mechanical engineering at Cornell University, where one of his professors was Carl Sagan,^[8] and graduated with a Bachelor of Science in 1977.^[9] He was awarded an honorary doctorate by The Johns Hopkins University in May 2008. In May 2011, Nye was awarded an Honorary Doctor of Science degree from Willamette University where he was the keynote speaker for that year's commencement exercises.^[10]

Nye began his career in Seattle at Boeing, where, among other things, he starred in training films and developed a hydraulic pressure resonance suppressor still used in the 747. Later he worked as a consultant in the aeronautics industry. Nye told the St. Petersburg Times in 1999 that he applied to be a NASA astronaut every few years but was always rejected.^[11]

The Science Guy[link]

Nye began his professional entertainment career as an actor on a local sketch comedy television show in Seattle, Almost Live!; Nye attempted to correct the host of Almost Live! after the host pronounced "gigawatt" as "jigowatt."^[12][13] The character name came from the host's comment "Who do you think you are—Bill Nye the Science Guy?" and Nye was thereafter known as such on the program. His other main recurring role on Almost Live! was as Speedwalker, a speedwalking Seattle superhero.

Coincidentally, in 1991–93 he appeared in the live-action educational segments of Back to the Future: The Animated Series with a nonspeaking role as an assistant to Dr. Emmett Brown, played by Christopher Lloyd, in which he would demonstrate science with Lloyd's voice-over. The segments' national popularity led to Nye's hosting the educational television program Bill Nye the Science Guy from 1993 to 1998. Each of the 100 episodes aimed to teach a specific topic in science to a preteen audience, yet it garnered a wide adult audience as well. The show was very popular as a school resource and is still used to this day. He has written several books as The Science Guy. In addition to hosting the show, he was also a writer and producer for the series, which was filmed entirely in Seattle.

When portraying "the Science Guy", Nye wears a light blue lab coat and a bow tie and takes on the persona of an excited, jocular science educator. This popular image of Nye has been parodied by numerous sources, including the webcomic xkcd^[14] and the satirical news organization The Onion.^[15][16] In response to the fake headline "Crack Nearly Killed Me," Nye took the joke in good humor and sent The Onion an email thanking them for "dealing compassionately with this matter."^[17]

He appeared in his Science Guy persona alongside Ellen DeGeneres and Alex Trebek in Ellen's Energy Adventure, an attraction that has played since 1996 at the Universe of Energy pavilion inside Epcot at Walt Disney World. He also has a voice-over at the DINOSAUR attraction in Disney's Animal Kingdom park, where he tells guests about the dinosaurs while they queue for the ride. In addition, he appears in the "Design Lab" of CyberSpace Mountain inside DisneyQuest at Walt Disney World, where he refers to himself as "Bill Nye the Coaster Guy."

[edit] Post-Science Guy career

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Bill Nye "The Science Guy" and Executive Director of The Planetary Society received the Committee for Skeptical Inquiry's "In Praise of Reason" Award at CSICON 2011 in New Orleans

Nye remained interested in science education through entertainment. He created a 13-episode PBS KCTS-TV series about science, called The Eyes of Nye, aimed at an older audience than his previous show had been. Airing in 2005, it often featured episodes based on politically relevant themes such as genetically modified food, global warming, and race.

He played a science teacher in Disney's 1998 TV movie The Principal Takes a Holiday; he made a hovercraft in order to demonstrate science in an unusual classroom manner. From 2000 to 2002, Nye was the technical expert in BattleBots. In 2004 and 2005, Nye hosted 100 Greatest Discoveries, an award-winning series produced by THINKFilm for The Science Channel and in high definition on the Discovery HD Theater. He was also host of an eight-part Discovery Channel series called Greatest Inventions with Bill Nye.

Nye has guest-starred in several episodes of the crime drama Numb3rs as an engineering faculty member. A lecture Nye gave several years ago on exciting children about math was an inspiration for creating the Numb3rs show.^[18]

Bill joined the American Optometric Association in a multimedia advertising campaign to educate parents on the importance of getting their children a comprehensive eye examination.^[19]

He was a regular in TV Land discussions. He has also made guest appearances on the VH1 reality show America's Most Smartest Model.^[20]

Nye appears in segments of The Climate Code on The Weather Channel, telling his personal ways of saving energy. He still makes regular appearances on the show, often asking quiz questions.

As of fall 2008, Nye also appears on the daytime game show Who Wants to Be a Millionaire as part of the show's reintroduced "Ask the Expert" lifeline. In 2008, he also hosted Stuff Happens, a show on the then new Planet Green network.

In November 2008, Nye appeared in an acting role as himself in the fifth-season episode "Brain Storm" of Stargate Atlantis alongside fellow television personality and astrophysicist Neil deGrasse Tyson.^[21]

Nye has appeared numerous times on the talk show Larry King Live, speaking about topics such as global warming^[22] and UFOs.^[23] He argued that global warming is an issue that should be addressed by governments of the world in part because it could be implicated in the record-setting 2005 Atlantic hurricane season. On UFOs he has been skeptical of extraterrestrial explanations for sightings such as those at Roswell and Malmstrom Air Force Base in 1967.

In 2009, portions of Bill Nye's shows were used as lyrics and portions of the second Symphony of Science science education music video by composer John Boswell.

Nye recorded a short YouTube video (as himself, not his TV persona) advocating clean energy climate change legislation on behalf of Al Gore's Repower America campaign in October 2009.^[24]

Nye (as his TV persona) also made a guest appearance on The Dr. Oz Show.

On March 12, 2011, Nye made an appearance on CNN to discuss the evolving nuclear incidents in Japan as a result of the devastating earthquake and tsunami there. Nye erroneously stated that cesium is used to "slow and control" the nuclear reaction. ^[25] In reality, cesium (specifically cesium-137) is a nuclear fission product, not a control rod material. Nye also erroneously stated that the nuclear reactor involved in the Three Mile Island incident is still running and that the use of boron to slow the nuclear chain reaction is uncommon, when in fact boron-10 is commonly used in control rods, and is circulated in the coolant of reactors in the United States, as well as stored on site as a method of emergency shutdown.^[26][27]

A solar noon clock atop Rhodes Hall was gifted from Nye to Cornell on Aug. 27 following a public lecture that filled the 715-seat Statler Auditorium. Nye talked about his father's passion for sundials and timekeeping, his time at Cornell, his work on the sundials mounted on the Mars rovers and the story behind the Bill Nye Solar Noon Clock. ^[28]

Life outside television[link]

Nye speaking in 2010.

In the early 2000s, Nye assisted in the development of a small sundial that was included in the Mars Exploration Rover missions. Known as MarsDial, it included small colored panels to provide a basis for color calibration in addition to helping keep track of time.^[29] From 2005 to 2010 Nye was the vice president of The Planetary Society, an organization that advocates space science research and the exploration of other planets, particularly Mars.^[30] He became the organization's second Executive Director in September 2010 when Louis Friedman stepped down.^[31][32]

In November 2010, Nye became the face of a new permanent exhibition at the Chabot Space & Science Center in Oakland, CA. Bill Nye’s Climate Lab features Nye as commander of the Clean Energy Space Station, and invites visitors on an urgent mission to thwart climate change. Beginning with a view of Planet Earth from space, visitors explore air, water, and land galleries to discover how climate change affects Earth’s connected systems, and how to use the Sun, wind, land, and water to generate clean energy. In an interview about the exhibit, Nye said, “Everything in the exhibit is geared to showing you that the size of the problem of climate change is big. Showing you a lot about energy use... It’s a huge opportunity... We need young people, entrepreneurs, young inventors, young innovators to change the world.” ^[33]

He holds several United States patents,^[34] including one for ballet pointe shoes^[30] and another for an educational magnifying glass created by filling a clear plastic bag with water.^[35][36] From 2001–2006 Nye served as Frank H.T. Rhodes Class of '56 University Professor at Cornell University.^[9][37] Nye supported the 2006 reclassification of Pluto from a planet to a dwarf planet by the International Astronomical Union.^[38]

Since 2006, Nye has lived in Los Angeles in a house with modifications, though has owned a house on Mercer Island.^{[citation needed]} As of July 2007, Nye and environmental activist Ed Begley, Jr. are engaging in a friendly competition "to see who could have the lowest carbon footprint," according to Begley.^[39] In a 2008 interview, Nye joked that he wants to "crush Ed Begley" in their environmental competition.^[40] Nye and Begley are neighbors in Los Angeles, and sometimes dine together at a local vegetarian restaurant.^[40] Nye often appears on Begley's Planet Green reality show Living with Ed.

Nye made an appearance in Palmdale's 2010 video "Here Comes the Summer"^[41]; the band's lead singer Kay Hanley is his neighbor.

Nye is a fellow of the Committee for Skeptical Inquiry, a U.S. non-profit scientific and educational organization whose aim is to promote scientific inquiry, critical investigation, and the use of reason in examining controversial and extraordinary claims.^[42]

Interviewed by John Rael for the Independent Investigation Group IIG, Nye stated that his "concern right now... scientific illiteracy... you don't [the public] have enough rudimentary knowledge of the universe to evaluate claims."^[43]

Personal life[link]

Nye announced his engagement during an appearance on The Late Late Show with Craig Ferguson and was married briefly to his fiancée of five months, author Blair Tindall, on February 3, 2006. The ceremony was performed by Rick Warren at The Entertainment Gathering at the Skirball Cultural Center in Los Angeles. Yo-Yo Ma provided the music.^[44] Nye left the relationship seven weeks later when the marriage license was declared invalid;^[45] their impromptu ceremony, which preceded the license purchase, violated California state law, said Tindall in a radio interview.^[46] Nye later secured a temporary restraining order against Tindall after she entered his property late at night to pour weed killer in his garden.^[45]

Nye enjoys baseball and occasionally does experiments involving the physics of the game. As a longtime Seattle resident before becoming an entertainer, he is said to have been a fan of the Seattle Mariners, although recently he has voiced his preference (as a D.C. native) for the Washington Nationals.^[6]

References[link]

External links[link]

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Biography portal

Wikimedia Commons has media related to: Bill Nye

• Official website
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• An interview/discussion with Nye as guest on the radio show Loveline
• "Changing The World With Science Education" interview on Point of Inquiry.
• Seattle Times interview (April 26, 2004)
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