2 What is Physics?Physics is a fundamental science that seeks to explain our physical environment (the universe).Physicists aim to formulate a few laws (statements) that apply to the whole universe and explain all observable phenomena.Physics is both experimental and theoretical. All theories are tested by experiments or observations.
3 What else is Physics?Physical theories seek to explain observations and predict new results.If two theories can explain observations, physicists will accept the simpler theory.Physicists use both inductive and deductive methods.
4 Physics is an experimental science It is based on observations with our senses or instruments.Physicists measure quantities (quantitative) as precisely as possible for comparison with theory and other experiments.Requires universal, accessible standards of measurement for reproducibility, comparability and accuracy of results.
5 Standards: Definitions of Fundamental or Base Quantities Fundamental quantities are agreed upon by convention.The minimum number of base quantities and their corresponding units are defined for simplicity and maintainability.Choice and definitions of standards and their corresponding units are based on accessibility, accuracy and universality.Example: time (second)
6 Standards: Definitions of Fundamental or Base Quantities Derived quantities are combinations of fundamental quantities. (Composite units)Units of derived quantities are usually chosen to honor a prestigious person or scientist.Example: Force (Newton, N)The Newton is a combination of kilograms, meters, and seconds
7 System of UnitsA collection of fundamental quantities and their associated units is called a system of units.The SI (Système International) is now used throughout the world except for the USA.Other system of units are the CGS, Imperial, and customary American systems.
8 The SI System (metric system) the 7 fundamental quantitiesQuantity Unit Symbollength meter mmass kilogram kgtime second stemperature degrees Celsius Celectric current ampere Aluminous intensity candela cdamount of substance mole molTwo Examples of Derived QuantitiesNewton: 1 N = 1 kg•m/s2Pascal: 1 Pa = 1 N/m2
9 Two ways to deal with very small or very large quantities Use scientific notationelectron rest mass = 9.11 x kgspeed of light in vacuum = x 108 m/sUse SI prefixesa very short laser pulse width = 100 fsradius of earth = 6.38 GmThe above methods also have the advantage of indicating clearly the number of significant figures.
10 SI Prefixes Prefix Abbreviation Value Link to more exa E 1018 peta Ptera Tgiga G 109mega M 106kilo k 103hecto h 102deka da 101deci dcenti cmilli mmicro mnano npico pfemto fatto aLink to more
11 Dimension The term “dimension” has two meanings in physics. It is used to describe the nature of space (3D space with length, width, height).It is also used to mean the “quality” or “type” of the physical quantity. (length, time, mass, force, etc.)We use the second meaning when we speak of dimensional consistency of physical equations.
12 Physics Equations Have Consistent Dimensions or Units Left and right side terms of equations must agree in terms of dimension (or units after conversion to common units)Algebraic operations also apply to units.Quantities to be added or subtracted must have the same units.Unit consistency or conversion of units follow the rules of algebra.
13 Two Examples of Equations with Dimensional Consistency
14 Significant Figures express the uncertainty of measured quantities Ex. (3 significant figures) 1.04 cm without an explicit plus/minus is usually interpreted as a length somewhere between and cm.least significant digit is the least reliable digit known only to a certain plus/minus valueEx ± 0.03 kg (4 significant figures)
15 Significant Figures cont... the number of significant figures of the result of algebraic operations (except for addition and subtraction) is determined by the least reliable input value.the decimal place of the result of addition/subtraction is the same as the least number of decimal places of the addends or subtrahends.
16 Significant Figures cont... the decimal place of the result of addition/subtraction is the same as the least number of decimal places of the addends or subtrahends.Number of significant figures of numbers added or subtracted are not used for rounding the result.4 sig. figs.hundredths dec. place3 sig. figs.hundredths dec. place4 sig. figs.thousandths dec. place2 sig. figs.hundredths dec. place
17 Significant Figures cont ... In this course we will not strictly enforce the rounding rules for addition. Usually, physics problems usually involve a series of calculations requiring additions, subtractions, multiplications, divisions, raising to a power, exponentiation, trigonometric functions, etc. Please keep the full number of decimal places of intermediate steps in your calculator and round only the answers to specific questions.There should not be any ‘calculator answers’