1-3-the-language-of-physics-physical-quantities-and-units_summary

This section focuses on the International System of Units (SI) and its use in physics. The learning objectives include associating physical quantities with their SI units, performing conversions among SI units using scientific notation, relating measurement uncertainty to significant figures and applying rules for using significant figures in calculations, and creating and interpreting graphs, including slope, y-intercept, inverse, quadratic, and logarithmic relationships. The section begins with an overview of the SI system and the base and derived quantities and units that compose it. Table 1.1 lists the base quantities and their corresponding SI base units. The meter, kilogram, second, ampere, kelvin, mole, and candle are the base units of length, mass, time, electric current, temperature, amount of substance, and luminous intensity, respectively. The definitons of the meter, kilogram, and second are lengthy but precise descriptions based on physical constants and properties. Metric prefixes are also discussed, including examples such as milli- for 0.001 and kilo- for 1000. In addition to the metric system, some common non-metric units are still used, particularly in the United States, such as inches, pounds, gallons, and miles. The conversion factors for these units can be combined with the appropriate units to convert values from SI to these other units or vice versa. Scientific notation is introduced as a convenient method of representing very large or small numbers. Negative exponents are used for fractions of one. Units of measurement can also be changed by moving the decimal point and including appropriate prefixes, such as milli- for 0.001 and kilo- for 1000. Calculations involving the conversion of units can be found in worked examples throughout the text. Accuracy, precision, and measurement uncertainty are discussed in the context of different levels of measurement accuracy and precision leading to different levels of uncertainty. The method of adding percents is introduced for approximating percent uncertainty in calculations when measurements are not exact. Graphing topics include an overview of linear, quadratic, inverse, logarithmic, and exponential relationships, as well as how to identify their mathematical relationships, including slope, y-intercept, and the equation of a line. Graphs may be linear (straight), quadratic (curved), line graphs, bar graphs, histograms, x-y plots, log plots, and log-log plots. Graphs are used extensively in physics to display trends, solve problems, and help illustrate complex phenomena.