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Chapter 1 : The Science of Physics

Chapter 1 : The Science of Physics. 1-1 Areas Within Physics. The Scientific Method. Make observations and collect data. This step leads to a question Formulate and test a hypothesis by experiments. Hypotheses must be testable Interpret results and revise the hypothesis as necessary

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Chapter 1 : The Science of Physics

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  1. Chapter 1 : The Science of Physics

  2. 1-1 Areas Within Physics

  3. The Scientific Method • Make observations and collect data. This step leads to a question • Formulate and test a hypothesis by experiments. Hypotheses must be testable • Interpret results and revise the hypothesis as necessary • State the conclusion in a form that can be evaluated by others.

  4. Why do we use models? • To reduce a complex phenomena to only those simple features that we wish to examine. • We use models because it is often impossible to describe all aspects of a complex phenomena at the same time.

  5. Physics Models • Describe only part of reality • Help build hypothesis • Help guide experimental design • Controlled experiment- experiment involving manipulation of only a single factor or variable

  6. 1-2 Measurements in Experiments • Seven fundamental dimensions (here are three) • Length – meter (m) • Mass – kilogram (kg) • Time – second (s)

  7. SI (Metric) Prefixes • 1012 tera T one trillion • 109 giga G one billion • 106 megaM one million • 103 kilo k one thousand • 100 unit m, L, g • 10-2centi c one-hundredth • 10-3milli m one-thousandth • 10-6 microµ one-millionth • 10-9nano n one-billionth

  8. Dimensional Analysis (Converting Units) • Establish conversion factor • Ex: 1000mm = 1 m • Set up equation from problem (37.2 mm = ? M) • Start with known • Ex: 37.2 mm

  9. Write conversion factor (units of known on bottom) • 37.2 mm 1 m 1000 mm • Multiply numbers across the top; divide by numbers on bottom • 37.2 mm 1 m = 3.72 x 10-2 1000 mm

  10. Accuracy – how close a measurement is to an accepted valuePrecision – degree of exactness to which a measurement is made

  11. Accuracy vs. Precision Low Accuracy/ High Precision/ High Accuracy/ Low Precision Low Accuracy High Precision

  12. Types of errors: • 1) method error- occurs when different methods are used to collect data • 2) instrument error- occurs when there is a problem with the measurement tool

  13. Significant Figures (also known as sig. figs.) Why use sig. figs? 1.) for consistency among scientists 2.) to limit certainty according to the limitations of our measuring devices

  14. Rules for Significant figures 1.) nonzero digits are always significant. • 96g • 2 significant figures • 61.4g • 3 significant figures

  15. 2.) One or more final zeros used after the decimal point are always significant. • 4.72 km • 3 significant figures • 4.7200 km • 5 significant figures

  16. 3.) Zeros between two other significant digits are always significant. • 5.029 m • 4 significant figures • 306 km • 3 significant figures

  17. 4.) Zeros used solely for spacing the decimal point (called placeholders) are not significant. • 7000g • 1 significant figure • 0.00783kg • 3 significant figures

  18. The Atlantic-Pacific Rule… -Just picture a map of the US. -Ask yourself a few questions, and…Presto!

  19. The Atlantic-Pacific Rule… 85400

  20. Addition and Subtraction-The answer can have no more digits to the right of the decimal point than are contained in the measurement with the least. • 12.52m + 349.0m + 8.241m = • 369.761 • round this to369.8m

  21. Multiplication and DivisionThe answer must contain no more significant figures than the measurement with the least amount. • 7.55m (0.34m) = • 2.576m2 • round to 2.6m2(0.34m has only two significant figures!)

  22. Rounding • If the last significant digit is followed by a 0, 1, 2, 3 or 4 round down • Ex: 14.531 becomes 14.53 • If the last significant digit is followed by a 6, 7, 8 or 9 round up. • Ex: 14.537 becomes 14.54

  23. Rounding Fives • If the last significant digit is even and is followed by a 5, and the 5 is followed by 0 or no other digits, round down • Ex: 32.250 becomes 32.2 • If the last significant digit is odd and is followed by a 5, and the 5 is followed by a nonzero digit, round up • Ex: 54.7511 becomes 54.8

  24. 1-3 The Language of Physics • Organizing Data • Tables • Graphs • Equations

  25. Abbreviations for Variables and Units

  26. Evaluating Physics Expressions • Dimensional analysis treats expressions as algebraic quantities • Units must agree • Place numbers to cancel out units • Order-of Magnitude • Estimate answer to problem before performing calculation to determine if answer is correct

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