The Branches of Physics

1. Chapter 1 Section 1 What Is Physics? The Branches of Physics Click below to watch the Visual Concept. Visual Concept

2. Chapter 1 Section 1 What Is Physics? The Branches of Physics

3. Chapter 1 Section 1 What Is Physics? Physics • The goal of physicsis to use a small number of basic concepts, equations,and assumptions to describe the physical world. • These physics principles can then be used to makepredictions about a broad range of phenomena. • Physics discoveries often turn out to have unexpected practical applications, and advances in technology can in turn lead to new physics discoveries.

4. Chapter 1 Section 1 What Is Physics? Physics and Technology

5. Chapter 1 Section 1 What Is Physics? The Scientific Method • There is no single procedure that scientists follow in their work. However, there are certain steps common to all good scientific investigations. • These steps are called thescientific method.

6. Chapter 1 Section 1 What Is Physics? Models • Physics usesmodelsthat describe phenomena. • A modelis a pattern, plan, representation, or description designed to show the structure or workings of an object, system, or concept. • A set of particles or interacting components considered to be a distinct physical entity for the purpose of study is called asystem.

7. Chapter 1 Section 1 What Is Physics? Hypotheses • Models help scientists develophypotheses. • Ahypothesisis an explanation that is based on prior scientific research or observations and that can be tested. • The process of simplifying and modeling a situation can help you determine the relevant variables and identify a hypothesis for testing.

8. Chapter 1 Section 1 What Is Physics? Hypotheses, continued Galileo modeled the behavior of falling objects in order to develop a hypothesis about how objects fall. If heavier objects fell faster than slower ones,would two bricks of different masses tied together fall slower(b)or faster(c)than the heavy brick alone(a)?Because of this contradiction, Galileo hypothesized instead that all objects fall at the same rate, as in(d).

9. Section 2 Measurements in Experiments Chapter 1 Preview • Numbers as Measurements • Dimensions and Units • Accuracy and Precision • Significant Figures • Vectors • Distance/Displacement Speed\Velocity

10. Section 2 Measurements in Experiments Chapter 1 Objectives • Listbasic SI units and the quantities they describe. • Convertmeasurements into scientific notation. • Distinguishbetween accuracy and precision. • Usesignificant figures in measurements and calculations.

11. Section 2 Measurements in Experiments Chapter 1 Numbers as Measurements • InSI,the standard measurement system for science, there areseven base units. • Each base unit describes asingle dimension,such as length, mass, or time. • The units oflength, mass,andtimeare themeter (m), kilogram (kg), andsecond (s),respectively. • Derived unitsare formed by combining the seven base units with multiplication or division. For example, speeds are typically expressed in units of meters per second (m/s).

12. Section 2 Measurements in Experiments Chapter 1 SI Standards

13. Section 2 Measurements in Experiments Chapter 1 SI Prefixes In SI, units are combined withprefixesthat symbolize certainpowers of 10.The most common prefixes and their symbols are shown in the table.

14. Section 2 Measurements in Experiments Chapter 1 Accuracy and Precision • Accuracyis a description of how close a measurement is to the correct or accepted value of the quantity measured. • Precisionis the degree of exactness of a measurement. • A numeric measure of confidence in a measurement or result is known asuncertainty.A lower uncertainty indicates greater confidence.

15. Section 2 Measurements in Experiments Chapter 1 Accuracy and Precision Click below to watch the Visual Concept. Visual Concept

16. Section 2 Measurements in Experiments Chapter 1 Measurement and Parallax Click below to watch the Visual Concept. Visual Concept

17. Section 2 Measurements in Experiments Chapter 1 Significant Figures • It is important to record theprecision of your measurementsso that other people can understand and interpret your results. • A common convention used in science to indicate precision is known assignificant figures. • Significant figuresare those digits in a measurement that are known with certainty plus the first digit that is uncertain.

18. Section 2 Measurements in Experiments Chapter 1 Significant Figures, continued Even though this ruler is marked in only centimeters and half-centimeters, if you estimate, you can use it to report measurements to a precision of a millimeter.

19. Section 2 Measurements in Experiments Chapter 1 Rules for Determining Significant Zeroes Click below to watch the Visual Concept. Visual Concept

20. Section 2 Measurements in Experiments Chapter 1 Rules for Determining Significant Zeros

21. Section 2 Measurements in Experiments Chapter 1 Rules for Calculating with Significant Figures

22. Section 2 Measurements in Experiments Chapter 1 Rules for Rounding in Calculations Click below to watch the Visual Concept. Visual Concept

23. Section 2 Measurements in Experiments Chapter 1 Rules for Rounding in Calculations

24. Section 3 The Language of Physics Chapter 1 Preview • Objectives • Mathematics and Physics • Physics Equations

25. Section 3 The Language of Physics Chapter 1 Objectives • Interpretdata in tables and graphs, and recognize equations that summarize data. • Distinguishbetween conventions for abbreviating units and quantities. • Usedimensional analysis to check the validity of equations. • Performorder-of-magnitude calculations.

26. Section 3 The Language of Physics Chapter 1 Mathematics and Physics • Tables, graphs,andequationscan make data easier to understand. • For example, consider an experiment to test Galileo’s hypothesis that all objects fall at the same rate in the absence of air resistance. • In this experiment, a table-tennis ball and a golf ball are dropped in a vacuum. • The results are recorded as a set of numbers corresponding to the times of the fall and the distance each ball falls. • A convenient way to organize the data is to form a table, as shown on the next slide.

27. Section 3 The Language of Physics Chapter 1 Data from Dropped-Ball Experiment A clear trend can be seen in the data. The more time that passes after each ball is dropped, the farther the ball falls.

28. Section 3 The Language of Physics Chapter 1 Graph from Dropped-Ball Experiment One method for analyzing the data is to construct a graph of the distance the balls have fallen versus the elapsed time since they were released. a The shape of the graph provides information about the relationship between time and distance.

29. Section 3 The Language of Physics Chapter 1 Physics Equations • Physicists useequationsto describe measured or predicted relationships between physical quantities. • Variablesand other specific quantities are abbreviated with letters that areboldfacedoritalicized. • Unitsare abbreviated with regular letters, sometimes called roman letters. • Two tools for evaluating physics equations aredimensional analysisandorder-of-magnitude estimates.

30. Section 3 The Language of Physics Chapter 1 Equation from Dropped-Ball Experiment • We can use the following equation to describe the relationship between the variables in the dropped-ball experiment: (change in position in meters) = 4.9  (time in seconds)2 • With symbols, the word equation above can be written as follows: y = 4.9(t)2 • The Greek letterD(delta) means“change in.”The abbreviationyindicates thevertical changeina ball’s position from its starting point, andtindicates thetime elapsed. • This equation allows you toreproduce the graphandmake predictionsabout the change in position for any time.

31. Chapter 3 Section 1 Introduction to Vectors Preview • Objectives • Scalars and Vectors • Graphical Addition of Vectors • Triangle Method of Addition • Properties of Vectors

32. Chapter 3 Section 1 Introduction to Vectors Scalars and Vectors • A scalaris a physical quantity that has magnitude but no direction. • Examples: speed, volume, the number of pages in your textbook • Avectoris a physical quantity that has both magnitude and direction. • Examples: displacement, velocity, acceleration • In this book, scalar quantities are initalics. Vectors are represented byboldfacesymbols.

33. Chapter 3 Section 1 Introduction to Vectors Graphical Addition of Vectors • A resultant vector represents the sum of two or more vectors. • Vectors can be added graphically. A student walks from his house to his friend’s house (a), then from his friend’s house to the school (b). The student’s resultant displacement (c) can be found by using a ruler and a protractor.

34. Chapter 3 Section 1 Introduction to Vectors Triangle Method of Addition • Vectors can be movedparallelto themselves in a diagram. • Thus, you can draw one vector with its tail starting at the tip of the other as long as the size and direction of each vector do not change. • Theresultant vectorcan then be drawn from the tail of the first vector to the tip of the last vector.

35. Chapter 3 Section 1 Introduction to Vectors Triangle Method of Addition Click below to watch the Visual Concept. Visual Concept

36. Chapter 3 Section 1 Introduction to Vectors Properties of Vectors Click below to watch the Visual Concept. Visual Concept

37. Chapter 3 Section 2 Vector Operations Coordinate Systems in Two Dimensions • One method for diagraming the motion of an object employsvectorsand the use of thex- and y-axes. • Axes are often designated usingfixed directions. • In the figure shown here, thepositive y-axispoints northand thepositive x-axispointseast.

38. Chapter 3 Section 2 Vector Operations Determining Resultant Magnitude and Direction • In Section 1, the magnitude and direction of a resultant were found graphically. • With this approach, the accuracy of the answer depends on how carefully the diagram is drawn and measured. • A simpler method uses thePythagorean theoremand thetangent function.

39. Chapter 3 Section 2 Vector Operations Determining Resultant Magnitude and Direction, continued The Pythagorean Theorem • Use thePythagorean theoremto find the magnitude of the resultant vector. • The Pythagorean theorem states that for anyright triangle,thesquare of the hypotenuse—the side opposite the right angle—equals the sum of the squares of the other two sides, or legs.

40. Chapter 3 Section 2 Vector Operations Determining Resultant Magnitude and Direction, continued The Tangent Function • Use thetangent functionto find the direction of the resultant vector. • For any right triangle, thetangentof an angle is defined as theratio of the opposite and adjacent legswith respect to aspecified acute angleof aright triangle.

41. Chapter 3 Section 2 Vector Operations Resolving Vectors into Components • You can often describe an object’s motion more conveniently by breaking a single vector into twocomponents,orresolvingthe vector. • The components of a vectorare the projections of the vector along the axes of a coordinate system. • Resolving a vector allows you toanalyze the motion in each direction.

42. Chapter 3 Section 2 Vector Operations Resolving Vectors into Components, continued Consider an airplane flying at 95 km/h. • Thehypotenuse (vplane)is theresultant vectorthat describes the airplane’stotal velocity. • The adjacent legrepresents thex component (vx),which describes the airplane’shorizontal speed. • Theopposite legrepresents they component (vy), which describes the airplane’svertical speed.

43. Chapter 3 Section 2 Vector Operations Resolving Vectors into Components, continued • Thesine and cosine functions can be used to find the components of a vector. • The sine and cosine functions are defined in terms of the lengths of the sides ofright triangles.

44. Chapter 3 Section 2 Vector Operations Adding Vectors That Are Not Perpendicular • Suppose that a plane travels first5 kmat an angle of35°,then climbs at10°for22 km,as shown below. How can you find thetotal displacement? • Because the original displacement vectors do not form a right triangle, you can not directly apply the tangent function or the Pythagorean theorem. d2 d1

45. Chapter 3 Section 2 Vector Operations Adding Vectors That Are Not Perpendicular, continued • You can find the magnitude and the direction of the resultant by resolving each of the plane’s displacement vectors into its x and y components. • Then the components along each axis can be added together. As shown in the figure, these sums will be the two perpendicular components of the resultant, d. The resultant’s magnitude can then be found by using the Pythagorean theorem, and its direction can be found by using the inverse tangent function.

46. Chapter 3 Section 4 Relative Motion Objectives • Describesituations in terms of frame of reference. • Solveproblems involving relative velocity.

47. Chapter 3 Section 4 Relative Motion Frames of Reference • If you are moving at80 km/hnorth and a car passes you going90 km/h, to you the faster car seems to be moving north at10 km/h. • Someone standing on the side of the road would measure the velocity of the faster car as90 km/htoward the north. • This simple example demonstrates that velocity measurements depend on theframe of referenceof the observer.

48. Chapter 3 Section 4 Relative Motion Frames of Reference, continued Consider a stunt dummy dropped from a plane. (a)When viewed from the plane, the stunt dummy falls straight down. (b)When viewed from a stationary position on the ground, the stunt dummy follows a parabolic projectile path.

49. Chapter 3 Section 4 Relative Motion Relative Motion Click below to watch the Visual Concept. Visual Concept

50. Chapter 3 Section 4 Relative Motion Relative Velocity • When solving relative velocity problems, write down the information in the form of velocities with subscripts. • Using our earlier example, we have: • vse = +80 km/h north (se = slower car with respect to Earth) • vfe = +90 km/h north (fe = fast car with respect to Earth) • unknown = vfs(fs = fast car with respect to slower car) • Write an equation forvfsin terms of the other velocities. The subscripts start withfand end withs.The other subscripts start with the letter that ended the preceding velocity: • vfs = vfe + ves