Chapter 1 : The Science of Physics

1-1 Areas Within Physics NameSubjectsExamples MechanicsMotion and its causesFalling objects, friction, weight, spinning objects ThermodynamicsHeat and temperatureMelting and freezing processes, engines, refrigerators Vibrations and wave phenomena Specific types of repetitive motions Springs, pendulums, sound OpticsLightMirrors, lenses, color, astronomy ElectromagnetismElectricity, magnetism, and light Electrical charge, circuitry, magnets RelativityParticles moving near the speed of light Particle collisions, particle accelerators, nuclear energy Quantum mechanicsBehavior of atomic and sub-atomic particles The atom and its parts

The Scientific Method 1.Make observations and collect data. This step leads to a question 2.Formulate and test a hypothesis by experiments. Hypotheses must be testable 3.Interpret results and revise the hypothesis as necessary 4.State the conclusion in a form that can be evaluated by others.

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.

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

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

SI (Metric) Prefixes teraTone trillion 10 9 gigaGone billion 10 6 megaM one million 10 3 kilokone thousand 10 0 unitm, L, g centicone-hundredth millimone-thousandth microµone-millionth nanonone-billionth

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

o Write conversion factor (units of known on bottom) 37.2 mm 1 m 1000 mm o Multiply numbers across the top; divide by numbers on bottom 37.2 mm 1 m = 3.72 x mm

Accuracy – how close a measurement is to an accepted value Precision – degree of exactness to which a measurement is made

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

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

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

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

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

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

4.) Zeros used solely for spacing the decimal point (called placeholders) are not significant g significant figure kg -3 significant figures

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

The Atlantic-Pacific Rule… 85400

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 m m m = round this to 369.8m

Multiplication and Division The answer must contain no more significant figures than the measurement with the least amount.  7.55m (0.34m) =  2.576m 2  round to 2.6m 2 (0.34m has only two significant figures!)

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

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 o Ex: 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 o Ex: becomes 54.8

1-3 The Language of Physics Organizing Data o Tables o Graphs o Equations

Abbreviations for Variables and Units QuantitySymbolUnitsAbbreviation Change in Position Δx, ΔymetersM Time Interval ΔtΔtsecondss massmkilogramskg

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