College Physics

1. College Physics Chapter 1 Introduction

2. Physics 2010/2011 Instructor: Allen Hunley Telephone: (931) 221-6116 (office) E-Mail: allen.hunley@muhlenberg.kyschools.us Office Hours: By appointment. (I am an adjunct member so I do not have an office at APSU.) Textbook:College Physics (7th Edition) by Serway & Faughn Thomson Books/Cole (2006)

3. World Wide Web Course Web Address: http://teacherweb.com/KY/MSHS/AllenHunley/ Textbook Web Address: www.cp7e.com (Physics Now Web Site, free if you purchased a new edition textbook)

4. Study Suggested Study Procedure 1. Read the assigned topics/materials before coming to the class/lab. 2. Attend the class, take good notes, and actively participate in all the activities in the class. 3. Reread the topics/materials. 4. Work the assigned problems starting the first day that they are assigned - you will require time for this material to "sink in"! 5. Ask questions in the interim. 6. Use a three-hole binder for the course so that you can keep all the materials (notes, homework assignments, answer sheets, exams, labs, etc.) in it. This will help you to find all the necessary materials when you prepare for your exams.

5. Evaluation Lecture and lab grades are combined. You will receive the same letter grade for the lecture course as for the lab course. In summary, the distribution of credits among the various assignments is as following: Guide to letter grades is: Homework Assignments 15 pointsA = 90 - 100 Lab Activities 20 points B = 80 – 89 Exams 50 points C = 70 – 79 Final Exam 15 points D = 60 – 69 Total 100 points F = 0 - 59

6. Laboratory Laboratory activities are highly valued in physics and are incorporated into our classes. These activities may consist of traditional hands-on experiments or computer simulations. You will be working in groups with 2-3 students in each group. The grade is based entirely on the lab write-ups you turn in. These activities contribute 20% of your grade.

7. The aims of the class 0 • On of the aims of this class is to teach you to think in a physics way. • As you see each concept, try to get a mental picture of how it works. • You will learn as much about how to solve problems as you do about the laws of physics themselves. • So you will need to approach this class differently from many of the other classes you are taking. Simply memorizing solutions will not help. • Doing lots of homework problems is the best way to do well in the class. As you do each problem, think of what strategy you are using to solve the problem.

8. The Branches of Physics

9. Physics • Physics attempts to use a small number of basic concepts, equations, and assumptions to describe the physical world. • These physics principles can then be used to make predictions 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.

10. Theories and Experiments • The goal of physics is to develop theories based on experiments • A theory is a “guess,” expressed mathematically, about how a system works • The theory makes predictions about how a system should work • Experiments check the theories’ predictions • Every theory is a work in progress

11. Chapter 1 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 the scientific method.

12. Chapter 1 Models • Physics uses models that describe phenomena. • A model is 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 a system.

13. Chapter 1 Hypotheses • Models help scientists develop hypotheses. • A hypothesis is 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.

14. Chapter 1 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).

15. Chapter 1 Controlled Experiments • A hypothesis must be tested in a controlled experiment. • A controlled experiment tests only one factor at a time by using a comparison of a control group with an experimental group.

16. Units • To communicate the result of a measurement for a quantity, a unit must be defined • Defining units allows everyone to relate to the same fundamental amount

17. Chapter 1 Numbers as Measurements • In SI, the standard measurement system for science, there are seven base units. • Each base unit describes a single dimension, such as length, mass, or time. • The units of length, mass, and time are the meter (m), kilogram (kg), and second (s), respectively. • Derived units are 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).

18. Systems of Measurement • Standardized systems • agreed upon by some authority, usually a governmental body • SI -- Systéme International • agreed to in 1960 by an international committee • main system used in this text • also called mks for the first letters in the units of the fundamental quantities

19. Systems of Measurements, cont • cgs – Gaussian system • named for the first letters of the units it uses for fundamental quantities • US Customary • everyday units • often uses weight, in pounds, instead of mass as a fundamental quantity

20. Length • Units • SI – meter, m • cgs – centimeter, cm • US Customary – foot, ft • Defined in terms of a meter – the distance traveled by light in a vacuum during a given time

21. Mass • Units • SI – kilogram, kg • cgs – gram, g • USC – slug, slug • Defined in terms of kilogram, based on a specific cylinder kept at the International Bureau of Weights and Measures

22. Mass The SI unit for mass is the kilogram. A kilogram is defined as the mass of a special platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures in France.

23. Time • Units • seconds, s in all three systems • 9,192,631,700 times the period of oscillation of radiation from the cesium atom.

24. Fundamental Quantities and Their Dimension • Length [L] • Mass [M] • Time [T] • other physical quantities can be constructed from these three

25. Chapter 1 Dimensions and Units • Measurements of physical quantities must be expressed in units that match the dimensions of that quantity. • In addition to having the correct dimension, measurements used in calculations should also have the same units. For example, when determining area by multiplying length and width, be sure the measurements are expressed in the same units.

26. Dimensional Analysis • Technique to check the correctness of an equation • Dimensions (length, mass, time, combinations) can be treated as algebraic quantities • add, subtract, multiply, divide • Both sides of equation must have the same dimensions

27. Dimensional Analysis, cont. • Cannot give numerical factors: this is its limitation • Dimensions of some common quantities are listed in Table 1.5

28. Example 1 The following equation was given by a student during an examination: Do a dimensional analysis and explain why the equation can’t be correct. ν has dimensions a has dimensions t has dimension

29. Example 2 Newton’s law of universal gravitation is represented by where F is the gravitational force, M and m are masses, and r is a length. Force has the SI units kg ∙ m/s2. What are the SI units of the proportionality constant G?

30. Prefixes • Prefixes correspond to powers of 10 • Each prefix has a specific name • Each prefix has a specific abbreviation • See table 1.4

31. Chapter 1 SI Prefixes In SI, units are combined with prefixes that symbolize certain powers of 10. The most common prefixes and their symbols are shown in the table.

32. Conversions • When units are not consistent, you may need to convert to appropriate ones • Units can be treated like algebraic quantities that can “cancel” each other • See the inside of the front cover for an extensive list of conversion factors • Example:

33. Chapter 1 Sample Problem A typical bacterium has a mass of about 2.0 fg. Express this measurement in terms of grams and kilograms. Given: mass = 2.0 fg Unknown: mass = ? g mass = ? kg

34. Chapter 1 Sample Problem, continued Build conversion factors from the relationships given in Table 3 of the textbook. Two possibilities are: Only the first one will cancel the units of femtograms to give units of grams.

35. Chapter 1 Sample Problem, continued Take the previous answer, and use a similar process to cancel the units of grams to give units of kilograms.

36. Converting UnitsExample 3 • Convert the following: • 25m to cm • 345m to Km • 550cm to Km • 0.3 m/s to Km/hr

37. Chapter 1 Mathematics and Physics • Tables, graphs, and equations can 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.

38. 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.

39. 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.

40. 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: Dy = 4.9(Dt)2 • The Greek letter D(delta) means “change in.” The abbreviation Dy indicates the vertical change in a ball’s position from its starting point, and Dt indicates the time elapsed. • This equation allows you to reproduce the graph and make predictions about the change in position for any time.

41. Coordinate Systems • Used to describe the position of a point in space • Coordinate system consists of • a fixed reference point called the origin • specific axes with scales and labels • instructions on how to label a point relative to the origin and the axes • Cartesian • Plane polar

42. Cartesian coordinate system • Also called rectangular coordinate system • x- and y- axes • Points are labeled (x,y)

43. Plane polar coordinate system • Origin and reference line are noted • Point is distance r from the origin in the direction of angle , ccw from reference line • Points are labeled (r,)

44. Trigonometry Review

45. More Trigonometry • Pythagorean Theorem • To find an angle, you need the inverse trig function • for example, • Be sure your calculator is set appropriately for degrees or radians

46. Problem Solving Strategy

47. Problem Solving Strategy • Read the problem • Identify the nature of the problem • Draw a diagram • Some types of problems require very specific types of diagrams

48. Problem Solving cont. • Label the physical quantities • Can label on the diagram • Use letters that remind you of the quantity • Many quantities have specific letters • Choose a coordinate system and label it • Identify principles and list data • Identify the principle involved • List the data (given information) • Indicate the unknown (what you are looking for)

49. Problem Solving, cont. • Choose equation(s) • Based on the principle, choose an equation or set of equations to apply to the problem • Substitute into the equation(s) • Solve for the unknown quantity • Substitute the data into the equation • Obtain a result • Include units

50. Problem Solving, final • Check the answer • Do the units match? • Are the units correct for the quantity being found? • Does the answer seem reasonable? • Check order of magnitude • Are signs appropriate and meaningful?