Lecture 2 Measurements

Lecture 2 Measurements - Lec2:Measurementsandunits

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Lec 2: Measurements and units 1 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 Scientific Method Why are measurements important? A hypothesis is a tentative and testable explanation for an observation or a series of observations. A scientific theory is a general explanation of widely observed phenomena that have been extensively tested. 2 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011
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Measurements ` Accurate measurements are essential for characterizing UNITS MATTER!! the physical and chemical properties of matter. ` Standardization of the units of measurements is essential. ` Quantitative easy to check ` Easy to agree upon, no personal bias ` The measuring instrument limits how good the measurement is. 3 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 SI Units Quantity Base Unit Abbrev. Symbol Length meter m l Mass Tim kilogram secon kg m Time Temp second Kelvin s K t T Amount mole mol n 4 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011
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Prefixes for SI units Prefixes Value Name Symbol Exponential 6 Mega M 10 Kilo k 10 3 Hecto h 10 2 Deka da 10 Deci d 10 -1 Centi c 10 -2 Milli m 10 -3 Micro μ 10 -6 Nano n 10 -9 Pico p 10 -12 5 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011 Derived units Quantity Name Symbol Area square meter m 2 Volume cubic meter m 3 Force newton N =kg.m/s 2 Pressure pasca Pa = 1N/m 2 pascal Energy joule J = 1 Kg.m 2 /s 2 Power watt W = J/s Electric charge coulomb C Current ampere A = C/s Voltage volt V = W/A = J/C Frequency hertz Hz 6 Roy A. Lacey, Stony Brook University; Che 131, Spring 2011
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How good are the measurements? We use two words to describe how good measurements are ` Accuracy how close the measurement is to the actual value ` Precision how well can the measurement be repeated All scientific measures are subject to error. 9 These errors are reflected in the number of figures reported for the measurement.
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This note was uploaded on 06/04/2011 for the course CHE 131 taught by Professor Kerber during the Spring '08 term at SUNY Stony Brook.

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Lecture 2 Measurements - Lec2:Measurementsandunits

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