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# Note for PH 101 at UA-General Physics I (1)

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This 23 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Alabama - Tuscaloosa taught by a professor in Fall. Since its upload, it has received 25 views.

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Date Created: 02/06/15

Chapter 1 Physics Principles with Applications 6 edition Giancoli GIANCOLI Chapter 1 n ro uction Measurement Estimating Copyright 2005 Pearson Prentice Hall Inc Units of Chapter 1 The Nature of Science Physics and Its Relation to Other Fields Models Theories and Laws Measurement and Uncertainty Significant Figures Units Standards and the SI System Converting Units Order of Magnitude Rapid Estimating Dimensions and Dimensional Analysis 11 The Nature of Science Observation important first step toward scientific theory requires imagination to tell what is important Theories created to explain observations will make predictions Observations will tell if the prediction is accurate and the cycle goes on 11 The Nature of Science How does a new theory get accepted Predictions agree better with data Explains a greater range of phenomena Copyright 2005 Pearson Prentice Hall Inc 12 Physics and Its Relation to Other Fields Physics is needed in both guy 5 3 architecture and engineering 1391 gt warmw39 w l 39 391 9 1 quot394 Other fields that use phySIcs mike 7439 and make contributions to it I ilt l l in 0 phySIology zoology life quot7 t L3 4 sciences 11 x III 3 37 1 3 E Physics provides the underlying laws for everything that happens in our universe Copyright 2005 Pearson Prentice Hall Incl n Phyeiee Rte Rele en fie ther F e de Communication between ereh teete and emg neere e eeeentel f d eee er ie e be eve e edn quot39 39 twig a a 4 m I r a n W I I g I a Copyright 2005 Pearson Prentice Hall Inc 13 Models Theories and Laws Models are very useful during the process of understanding phenomena A model creates mental pictures care must be taken to understand the limits of the model and not take it too seriously A theory is detailed and can give testable predictions A law is a brief description of how nature behaves in a broad set of circumstances A principle is similar to a law but applies to a narrower range of phenomena 14 Measurement and Uncertainty Significant Figures No measurement is exact there is always some uncertainty due to limited instrument accuracy and difficulty reading results The photograph to the left illustrates this it would be difficult to a measure the width of this 2x4 to better than a l M 1 My millimeter i3 9 Iiium39n n uvIH w m 14 Measurement and Uncertainty Significant Figures Estimated uncertainty is written with a 1 sign for example 88 01 cm Percent uncertainty is the ratio of the uncertainty to the measured value multiplied by 100 01 X 1000 w 103 88 C 14 Measurement and Uncertainty Significant Figures The number of significant figures is the number of reliably known digits in a number It is usually possible to tell the number of significant figures by the way the number is written 2321 cm has 4 significant figures 0062 cm has 2 significant figures the initial zeroes don t count 80 km is ambiguous it could have 1 or 2 significant figures If it has 3 it should be written 800 km Significant Figures Example in multiplication of lengths 113 cm x 68 cm 7684 cm2 area But with 01 cm uncertainty in each length this could just as easily be 112 x 67 7504 or 114 x 69 7866 So we would write the result as 77 cm2 this implies at least 7711 cm2 14 Measurement and Uncertainty Significant Figures When multiplying or dividing numbers the result has as many significant figures as the number used in the calculation with the fewest significant figures Previous Example 113 cm x 68 cm 77 cm 68 cm had 2 sf so the result should have 2 sf When adding or subtracting the answer is no more accurate than the least accurate number used 14 Measurement and Uncertainty Significant Figures Calculators will not give you the right number of significant figures they usually give too many but sometimes give too few especially if there are trailing zeroes after a decimal point The top calculator shows the result of 20 I 30 The bottom calculator shows the 33 result of 25 x 32 l nunmaf b Copyright 2005 Pearson Prentice Hall Inc Scientific Notation For many very large or very small numbers which we often meet in physics we use scientific notation or 39powers of ten39 Examples 36900 369 x 104 36900000000000000 369 x1015 0000000021 21 x 10 398 Note sometimes this is written 369e4 where 39e439 is short for 39 x 10439 It39s easy to use sf when combined with this notation 15 Units Standards and the SI System Quantity Unit Length Time Mass Meter Second Kilogram Standard Length of the path traveled by light in 1299792458 second Time required for 9192631770 periods of radiation emitted by cesium atoms Platinum cylinder in International Bureau of Weights and Measures Paris TABLE 14 Metric SI Prefixes Pre x Abbreviation Value yotta Y 1024 zetta z 1021 exa E 1018 peta P 1015 tera T 1012 giga G 109 mega M 106 kilo k 103 hecto h 102 deka da 101 deci d 10 centi C 10 2 milli 111 10 3 microT u 10 6 nano n 10 pico p 10quot12 femto f 10quot5 atto a 103918 zepto z 10 21 yocto y 103924 i p is the Greek letter mu Copyright 2005 Pearson Prentice Hall Inc I5 Units Standards and the SI System These are the standard SI prefixes for indicating powers of 10 Many are familiar Y Z E h da a z and y are rarely used 15 Units Standards and the SI System We will be working in the SI system where the basic units are kilograms meters and seconds TABLE 1 5 SI Base Quantities and Units Unit Abbre Quantity Unit viation Length meter In Time second 5 Mass kilogram kg Electric current ampere A Temperature kelvin K Amount of substance mole m0 Luminous intensity candela cd Copyright 2005 Pearson Prentice Hall Inc 16 Converting Units Converting between metric units for example from kg to g is easy as all it involves is powers of 10 17 Order of Magnitude Rapid Estimating Q A quick way to estimate a a calculated quantity is to round off all numbers to one significant figure and then calculate Your result should at least be the right order of magnitude this can be expressed by rounding it off to the nearest power of 10 a a 131 Diagrams are also very useful in making estimations Copyright 2005 Pearson Prentice Hall Inc 18 Dimensions and Dimensional Analysis Dimensions of a quantity are the base units that make it up they are generally written using square brackets Example Speed distance time Dimensions of speed LIT Quantities that are being added or subtracted must have the same dimensions In addition a quantity calculated as the solution to a problem should have the correct dimensions Summary of Chapter 1 Theories are created to explain observations and then tested based on their predictions A model is like an analogy it is not intended to be a true picture butjust to provide a familiar way of envisioning a quantity A theory is much more welldeveloped and can make testable predictions a law is a theory that can be explained simply and which is widely applicable Dimensional analysis is useful for checking calculations Summary of Chapter 1 Measurements can never be exact there is always some uncertainty It is important to write them as well as other quantities with the correct number of significant figures The most common system of units in the world is the SI system When converting units check dimensions to see that the conversion has been done properly Orderof magnitude estimates can be very helpful

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