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INTRODUCTION

INTRODUCTION. The “stuff” every Physics student should know…. The Metric System. Based on powers ten Standards of the metric system: SI units – provides a set of standards of measurement, because it is convenient.

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INTRODUCTION

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  1. INTRODUCTION The “stuff” every Physics student should know…

  2. The Metric System • Based on powers ten • Standards of the metric system: SI units – provides a set of standards of measurement, because it is convenient. • Fundamental unit – the base units from which all quantities can be described. • Examples: Length – meter(m) Mass – kilogram(kg) Time – second(s)

  3. The Metric System • Derived Unit – combinations of the base units • Examples: m/s, m/s/s, Joule • Can you think of any others?

  4. The Metric System • Prefixes for the Metric System: Femto (F) 10-15 Pico (p) 10-12 Tera (T) 1012 Nano (n) 10-9 Giga (G) 109 Micro () 10-6 Mega (M) 106 Milli (m) 10-3 Kilo (k) 103 Centi (c) 10-2 Hecto (h) 102 Deci (d) 10-1 Deka (da) 101

  5. The Metric System Conversions – when moving to a larger unit from a smaller unit, move the decimal point to the left the number of spaces (steps) between the prefixes, When moving to a smaller unit from a larger unit, move the decimal point to the right the number of spaces (steps) between the prefixes. DRUL RULE: down to the right, up to the left

  6. The Metric System The Factor- Label Method – converting from one unit to another using a conversion factor. • A conversion factor is a fraction that is equal to the number 1. • See the worksheet labeled Unit Conversions and Factor Label Method

  7. Uncertainty In Measurement All measurements are subject to uncertainties. For example: • Parallax – the apparent shift in the position of an object when it is viewed from different angles To avoid this and other discrepancies, we need: Precision – the degree of exactness of a measurement • It is limited by the smallest division on the measurement scale

  8. Uncertainty In Measurement Accuracy – how well the results of an experiment agree with the standard value. • Because precision of measuring devices is limited, so is the number of digits in the measurement. • See overhead and handout on Accuracy and Precision

  9. Significant Figures – “Sig Figs” Sig figs – the valid digits in a measurement • All digits 1-9 are significant (123 – three sig figs) • Zeros between sig. digits are always significant (5.007 – 4 sig figs) • Trailing zeros in a number are only significant if the number contains a decimal point. ( 100.0 – 4 sig figs but 100 – 1 sig fig)

  10. Significant Figures – “Sig Figs” • Zeros in the beginning of a number whose only function is to place the decimal point are not significant (0.0025 – 2 sig figs) • Zeros following a decimal significant fiure are significant (0.000470 – 3 sig figs, 0.47000 – 5 sig figs)

  11. Significant Figures – “Sig Figs” Rules for calculations using Significant Figures • When multiplying and dividing, limit and round to the least number of significant figures in any of the factors. • When adding and subtracting, limit and round your answer to the least number of decimal places in any of the numbers that make up your answer.

  12. Significant Figures & Scientific Notation To avoid confusion with significant figures, we put measurements in scientific notation. This way all significant figures come before the power of ten. Examples: 156,000 1.56 x 105 0.026 2.6 x 10-2 0.1260 1.260 x 10-4 When performing operations with sig figs, the answer is only as precise as the lesser precise value. See w.s. on calculations with sig figs

  13. Graphing Data Independent Variable – the variable that is changed or manipulated, the experimenter can control directly (x –axis) Dependent Variable – the responding variable, this depends on the independent variable (y – axis) Slope = rise = y run x

  14. Graphing Data Linear relationship – the dependent variable varies linearly with the independent; the two are directly proportional y = mx + b • Direct relationship – as one increases, so does the other • Indirect (Inverse) relationship – as one increases, the other decreases

  15. Graphing Data Quadratic relationship – one variable depends on the inverse of the other (the graph is called the parabola) y = mx2 y = kx2 • Inverse relationship – one variable depends on the inverse of the other y = k(1/X) = k/x or k = xy or y = kx-1

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