1164694436 - Fundamental Units, Length, & Time. Fall...

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Fundamental Units, Length, & Time. Fall 2006 – 2007 Prof Ramsey Hamade Ghosn Bldg, 406 rhamade@aub.edu.lb
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(1) Fundamental Dimensions in answer to the following questions ± How tall are you? ± How far do you live? ± How long it takes you to get to AUB? ± How old are you? ± How long does it take to boil an egg? ± How heavy is your backpack? ± How warm or cold is it outside?
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Fundamental dimensions (The Basic Seven) ± Using these, one can derive all other necessary physical quantities that are necessary to describe nature ± These quantities can be scaled or divided: Time for example can be divided into small or large portions such as seconds, minutes, hours, days, weeks, months, years, decades, centuries, millennia… 1. Length 2. Mass and weight 3. Time 4. Temperature 5. Electric current 6. Amount of substance 7. Luminous intensity
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Motivation behind this discussion: 1. Student to develop a “ Feel ” for units. This makes for a better engineer . 2. These divisions of physical dimensions are used appropriately to keep numbers manageable . 3. The units for other physical quantities used can be derived from the base units.
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± In the International system of units (SI) Physical quantity Name of base unit Symbol Length Meter m Mass Kilogram Kg Time Second S Electric current Ampere A
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Physical quantity Name of base unit Symbol Thermodynamic Temperature Kelvin K Amount of Substance Mole mol Luminous Intensity Candela cd
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Formal definitions of some base units ± The meter (m): The length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second ± The kilogram (Kg): equal to the mass of international prototype of the kilogram
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± The second (S): The duration of 9,192,631,770 periods of the radiation corresponding to the transition between to hyperfine levels of the ground state of cesium (Cs) 133 atom ± The Kelvin (K): a unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
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± The Mole (mol): http://whatis.techtarget.com/definition/0,,sid9_gci525907,00.html SI The mole (abbreviation, mol) is the Standard International ( ) unit of material quantity. One mole is the number of atom s in precisely 12 thousandths of a kilogram (0.012 kg) of C-12, the most common naturally-occurring isotope of the element carbon. This number is equal to approximately 6.022169 x 10 23 , and is also called the Avogadro constant . The mole is the only fundamental SI unit that is dimensionless. That means it represents a simple numerical quantity or value; it is a term similar in nature to "dozen" (meaning 12) or "gross" (meaning 144). But 1 mol is, unlike a dozen or a gross, an incomprehensibly large number. Written out in decimal form, it appears as 602,216,900,000,000,000,000,000 . Envision a huge cubical box measuring about 84 kilometers (84 km) on each edge. Then imagine that box being neatly packed full of sand-grain-size cubes measuring a millimeter (1 mm) on an edge. If this were done, the box would contain roughly 1 mol of cubes.
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Example of derived units
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1. Student to develop a “ Feel ” for units. This makes for a better engineer
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Prefixes and symbols
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This note was uploaded on 02/07/2011 for the course MECH 200 taught by Professor Drramseyhamady during the Fall '06 term at American University of Beirut.

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1164694436 - Fundamental Units, Length, & Time. Fall...

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