PHY 110 Introduction to Physics Dr Henry SC

PHY 110, Introduction to Physics Dr. Henry SC 453, 572 -6164 (alt 572 -5309) E-Mail: henryh 1@nku. edu Web Site: www. nku. edu/~henryh 1/ Do not leave Voice Mail Messages Use E-Mail Instead © Hugh Henry, 2008

PHY 110, Introduction to Physics Dr. Henry SC 453, 572 -6164 (alt 572 -5309) © Hugh Henry, 2008

PHY 110, Introduction to Physics • “Physics is either impossible or trivial. It is impossible until you understand it. . . then it becomes trivial. ” – Ernest Rutherford (1871 -1937)

PHY 110, Introduction to Physics • Rutherford also said: “In science there is only physics; everything else is stamp collecting. ”

PHY 110, Introduction to Physics Rutherford’s comments are related: • Physics is logic – not memorization • Physics is a Way of Thinking that may be unfamiliar – But when you catch on, it’s much easier!!

Textbooks • (Inquiry into) Physics • Ostdiek and Bord • 1 st Edition (2011 -2011)

Textbooks 6 th Edition (left) and 5 th Edition (right) Almost Identical – OK If You Can Get them Cheap

Lab Manual • Posted in Blackboard as pdf files • Students are expected to download and print prior to each lab session. • One lab report per group of 3 -5 students • Lab report includes graphs – Graph paper 10 x 10 per inch (or finer) must be obtained and brought to lab sessions. (Available at cost in lab. )

Course Syllabus is available online http: //www. nku. edu/~henryh 1/Syllabus. htm OR NKU’s Blackboard System

Syllabus Questions? ? “Students are responsible to read and understand all items on this syllabus before the first class. “Any items not understood must be brought to the attention of the instructor within the first two weeks of class. “THE SYLLABUS WILL NOT BE REVIEWED OR DISCUSSED IN CLASS, EXCEPT TO ANSWER QUESTIONS. ”

Course Essentials • • Online Honor Quiz every 2 weeks (approx) Midterm and Final Exams are proctored Quizzes and Exams are curved No lab makeups – but Tuesday students can come Thursday (and vice versa) – 90% class attendance 1 free lab cut • Up to 5% extra credit is allowed • Students must check Blackboard at least weekly for assignments and lab download

Course Essentials Grading based on: • Honor Quiz Average – 28% • Midterm Exam – 27% • Final Exam – 35% • Lab grade – 10% • Extra credit is added to student’s net score

Personal Responsibility • This is America! – you can accomplish whatever you set your mind to do – . . . but you have to work at it • There are no victims in this class – Everyone will be equally abused without regard to race, religion, sexual preference, or socioeconomic background • Grading is based strictly on tests and labs – Plus any Extra Credit work (good for up to 5 points added to your final grade) 13

If you are Tardy Initial beside Your Name on the Sheet on the Front Table

Introduction

Superconductivity My Background Medical Physics: 16 Ultrasound/Radiation Oncology

Physics Helps Us Understand the World around Us

Physics is all around us 18

Acceleration 19

Deceleration 20

Golf and Tennis use Physics 21

Pool uses Physics 22

Physics on Ice 23

Football uses Physics 24

Space Program based on Physics 25

Physics Helps Understand the World Around Us 26

BP Oil Leak n Why was it so hard to “Plug the damn hole” (Pres Obama) at the BP Deep Water Horizons Oil leak in 2010? n We will learn as we study chapter 4. n Physics helps us understand the world around us

Modern Physics is a very new Science A brief look at the history of Physics. . .

Physics Began with the Ancient Greeks Greek “science” was philosophy – ignoring experimentation and mathematics – even though the Greeks developed geometry. Democritus and Leuccipus and proposed atomic theory in the 5 th century BC Thales of Miletus 624 -546 BC Pythagoras of Samos 570 -500 BC Democritus of Abdera 460 -370 BC

Aristotle’s philosophy dominated “physics” until Galileo and Newton Plato (427 -347 BC) Aristotle (384 -322 BC) The School of Athens, 30

The Middle Ages • After the Roman Empire fell, the West plunged into what is called the “Dark Ages, ” and Greek science was forgotten. • Aristotle’s physics was “rediscovered” in the West ~1000 AD. • Thomas Aquinas (1225 -1274) incorporated it into Roman Catholic theology – including the geocentricity principle. – The Sun and planets circle the Earth 31

The Protestant Reformation • The 16 th century Protestant Reformation encouraged scientific inquiry • Nature was no longer believed shrouded in mystery – “Since the creation of the world God’s invisible qualities . . . have been clearly seen. . . from what has been made” (Romans 1: 20) Martin Luther’s 95 Theses, 1517 32

Galileo Pioneered Experimental Physics Galileo, 1564 -1642 33

Galileo Pioneered Experimental Physics • The science of the ancient Greeks involved thinking about the way the world works • Galileo did experiments to see how the world really works. 34

Aristotle. . . Wrong on Gravity n Aristotle “didn’t do silly experiments, but proved truth with impeccable logic. ”* n n He believed a large ball would fall to earth faster than a small ball. A simple experiment would have falsified this theory. n It took almost 2000 years before Galileo finally did this experiment. n With Galileo, much of Aristotle’s physics begins to fall apart. Aristotle (384 -322 BC) *Marshall Brucer, A Chronology of Nuclear Medicine (St. Louis: Heritage Publicationss, 1990) 8.

Experiment is Modern Physics’ Gold Standard Galileo’s Incline Plane Experiment 36

Aristotle. . . Wrong on The Planets n Copernicus and Galileo demonstrated from observation and mathematics that the Earth and the planets circle the Sun. Aristotle (384 -322 BC)

Inquisition of Galileo, 1633 AD Yet 17 th century scientists believed Aristotle that the Sun circled the Earth; they scorned Galileo’s Mathematics and Observation 38

“Settled Science” n The next time you hear a claim that “ 99% of scientists agree” or that something is “Settled Science, ” remember Galileo! 99% of 17 th century scientists thought the sun circled the Earth. n Science is not determined by majority vote – and those who make such claims do so as a substitute for scientific proof. n n “Methinks the lady doth protest too much” – Shakespeare

Sir Isaac Newton, 1642 -1727 Father of Experimental Research 40

Since Experimental Physics is Relatively Recent, so are Most Key Principles of Physics: • Settlement of Jamestown: 1607 • Newton’s Principia (Chapter 2) ~1687 • American Revolution: 1776 -1781 • Electromagnetism (Chapter 8) ~1830 • Conservation of Energy (Chapter 3) and Laws of Thermodynamics (Chapter 5) ~1850 • American Civil War 1861 -1865 • Relativity (Chapter 12) ~1910 41

Albert Einstein, 1879 -1955 E=mc 2 Relativity 42

Person of the Century 43

The Electronics Modern People Take for Granted was Mostly Developed over Our Lifetimes

Slide Rule • This was the “computer” used by scientists into the 1970’s – I did most of my Ph. D. work with a slide rule 45

Punchcard Computers 1960’s 46

1970 PDP 11 Computer 47

1972 HP 35 Hand-held, “Electronic Slide Rule” 48

Later 70’s Solar Cells (Cheap Calculators) Modern TI BA 35 49

Most Advances in Physics have Happened in Our Lifetimes

Physics is a Way of Thinking

Modern Scientific Method • • Hypothesis Experiment Analysis Feedback OR • Observation • Explanation • Feedback 52

Ask Questions Seek Answers Question the Questions 53

Practical Scientific Method 54

55

Using the Scientific Method Helps Differentiate Real Science from Trans-Science and Politicized Science

Beware the “Scientific. Technological Elite” n “The prospect of domination of the nation's scholars by Federal employment, project allocations, and the power of money is ever present – and is gravely to be regarded. . We must also be alert to the. . . danger that public policy could itself become the captive of a scientifictechnological elite. ” President Eisenhower's Farewell Address to the Nation January 17, 1961 http: //www. informationclearinghouse. info/article 5407. htm

Alvin Weinberg’s “Trans-Science” • “Questions that can be stated in scientific terms but that are. . . beyond the proficiency of science to answer”. . . [are] “Trans-Scientific” 58 Alvin Weinberg, Science, 177: 211 (21 July 1972)

Use your intellect. . . follow the scientific method of logical analysis in all areas of life Ask Questions Seek Answers Question the Questions 59

Chapter 1 The Study of Motion © Hugh Henry, 2008

Measurement is an Essential Part of the Scientific Method In order to analyze a system scientifically, it must be measurable and quantitative information obtained

Qualitative vs Quantitative Mathematics vs Philosophy • “Tall” or 6’ 8” • “Far” or 1896 miles • “Fast” or 145 mph 62

Furthermore, to communicate quantitative information, there must be consistency of units 63

Some Different Units Used to Measure Distance 241 kilometers 241, 402 meters 64

Magna Carta, 1215 The Great Charter Included standardized weights and measures among rights granted Englishmen by King John

Inconsistent Units and Christopher Columbus’ Big Miscalculation: n 15 th century scholars did NOT think the world was flat n But Columbus underestimated the Earth’s circumference by ~36% because he thought an astronomer’s calculation of 20, 400 miles was in Italian miles (~1. 238 km) – but it was in Arabic miles (~1. 830 km). n The real circumference is 24, 902 English miles (1. 610 km/mile): 40, 076 km

Fundamental Physical Quantities n. Distance: d n. Time: t n. Mass: m 67

Units n We can classify almost all quantities in terms of the fundamental physical quantities: Distance n Mass n Time n n d m t For example: § Speed has units d/t (miles per hour) 68

Unit Consistency We will discuss three standards of units: n Metric Units: n SI (Système International) Units: n n d = meters (m) m = kilograms (kg) t = seconds (s) CGS Units: n n n d = centimeters (cm) m = grams (g or gm) t = seconds (s) 69

Unit Consistency, cont’d n British (or English) Units: n n n d = feet (ft) m = slugs or pound-mass (lbm) t = seconds (s) n We will use mostly SI but we need to know how to convert back and forth. 70

British vs Metric (SI) Systems n Inches, Feet, Miles n Centimeters, Meters, n Hours, Minutes, Kilometers n Hours, Minutes, Seconds n Milligrams, Grams, Kilograms Seconds n Slugs 71

Fundamental Physical Quantities n. Distance: d n Time: t n Mass: m 72

Distance

Converting units n The “Special Review Card” in the back of the textbook provides numerous conversions. Here are some of them: n n 1 inch 1 mile 1 km = = 2. 54 cm 3. 281 ft 5280 ft 0. 621 mi 74

Converting units, cont’d Here is the procedure to convert units: n Look at your original units. n Determine the units you want to have. n Find the conversion factor(s) you need. n Multiply the original unit by a fraction equal to one (1) that the net effect of replacing the original unit with the desired new unit. n The following examples illustrate this principle 75

Example A yacht is 20 m long. Express this length in feet. ANSWER: 76

Example It may be necessary to do this more than once: How many liters are in a five gallon bucket? There are four quarts in a gallon. ANSWER: 77

Converting units, cont’d n We can use this principle to convert a compound unit through successive multiplications by one (1): 78

British and Metric (SI) Systems Non-Decimal vs Decimal

Metric prefixes n Sometimes a unit is too small or too big for a particular measurement. n To overcome this, we use a prefix. 80

millimeters vs kilometers 81

Metric prefixes, cont’d Power of 10 1015 1012 109 106 103 10 -2 10 -3 10 -6 10 -9 10 -12 10 -15 Prefix peta tera giga mega kilo centi milli micro nano pico femto Symbol P T G M k c m m n p f 82

Metric prefixes, cont’d • Some examples: – 1 centimeter = 10 -2 meters = 0. 01 m – 1 millimeter = 10 -3 meters = 0. 001 m – 1 kilogram = 103 grams = 1, 000 g 83

deci. . . centi. . . milli 84

Scientific Notation If you don’t know it already, learn it now!

Express large or small numbers as powers of 10 • 2, 210, 000, 000 2. 21 * 1012 • 0. 0000000789 7. 89 * 10 -8 • Many of you will try to work with these numbers using a hand-held calculator – But it’s more reliable to do it the “old-fashioned” way • (2. 21 * 1012) * (7. 89 * 10 -8) 2. 21 * 7. 89 * 1012 -8 17. 4369 * 104 1. 74369 * 105 86

Significant Figures Round off the above answer: 1. 74369 * 105 1. 744 * 105 OR 1. 74 * 105

Laboratory Exercises: Data Analysis Taking the Data Charting the Data Graphing the Data 88

Graphing the Data • Independent Variable on “X” Axis • Dependent Variable on “Y” Axis $0. 80 89

Graphing Non-linear Data not on a straight line 90

Experimental Error For a variety of reasons – precision of setup, human error, etc – data measured in laboratory exercises will be in error Calculate “Experimental Error”: • Experimental Error = 100% * (dc – dm)/dc where dc is correct data, dm is measured data 91

Fundamental Physical Quantities n Distance: d n. Time: t n Mass: m 92

Frequency and period n We define frequency as the number of events per a given amount of time. n When an event occurs repeatedly, we say that the event is periodic. n The amount of time between events is the period. 93

Frequency n The number of cycles of a periodic process that occur per unit time n Standard unit: Hertz (Hz) = 1/s

Period is the time for one complete cycle for a process that repeats It is abbreviated T, and the units are time units

Frequency and period, cont’d n The symbols we use to represent frequency and period are: frequency: f n period: T n n They are related by 96

Frequency and period, cont’d n The standard unit of frequency is the Hertz (Hz). n It is equivalent to 1 cycle per second. 97

Example 1. 1 A mechanical stopwatch uses a balance wheel that rotates back and forth 10 times in 2 seconds. What is the frequency of the balance wheel? ANSWER: 98

The pendulum in this clock rotates back and forth 10 times in 20 seconds What is the period of the pendulum? ANSWER: • T = 20 s/10 cycles • = 2 s 99

Defining the Meter n A meter is defined as one ten-millionth of the length of the Earth’s meridian along a quadrant. n The dimensions of the Earth were known many, many years ago n An early definition was the length of a pendulum with a half-period of 1 second. n n n T = 2 sec f = 0. 5 Hz The period of a pendulum will be discussed in chapter 2

Fundamental Physical Quantities n Distance: d n Time: t n. Mass: m 101

Mass vs Weight Mass Weight

Fundamental Physical Quantities n. Distance: d n. Time: t n. Mass: m 103

Other Physical Quantities are Derived (Calculated) from d, t, m n. Speed: v = d/t n. Frequency: f = 1/t (1/T) n. Weight: w= mg 104

Speed n Speed is the rate of change of distance from a reference point. n It is the rate of movement. n It equals the distance something travels divided by the elapsed time. 105

Speed

Speed, cont’d n In mathematical notation, n So we can write speed as 107

Change in Distance (d) Speed (v) = Change in Time (t) = (df - di) / (tf - ti) = Dd / Dt

Average vs Instantaneous Speed n The symbol D is the Greek letter delta and represents the change in. n As the time interval becomes shorter and shorter, we approach the instantaneous speed. Avg vs Instant Speed 109

Calculate Average Speed of Flo Jo in the 100 meter dash Avg Speed = Δd / Δt = (df - di) / (tf - ti) = 100 – 0 m / 10. 5 – 0 s = 100 m / 10. 5 s = 9. 52 m/s

Calculate Her Average Speed over the last 40 meters Avg Speed = Δd / Δt = (df - di) / (tf - ti) = 100 – 60 m / 10. 5 – 6. 85 s = 40 m / 3. 65 s = 10. 96 m/s

Speed, cont’d n If we know the average speed and how long something travels at that speed, we can find the distance it travels: 112

Speed, cont’d n We say that the distance is proportional to the elapsed time: n Using the speed gives us an equality, i. e. , an equal sign, so we call v the proportionality constant. 113

Speed of Sound and Speed of Light d = vt v = d/t 114

Example When lightning strikes, you see the flash almost immediately but the thunder typically lags behind. The speed of light is 3 × 108 m/s and the speed of sound is about 345 m/s. If the lightning flash is one mile away, how long does it take the light and sound to reach you? 115

Example ANSWER: For the thunder: For the flash: 116

Speed, cont’d n Note that speed is relative. n It depends upon what you are measuring your speed against. n Consider a woman running at 8 mph on a ship moving at 20 mph. 117

Speed, cont’d n If you are clocking her speed on the ship, you see her moving at 118

Speed, cont’d n If you are clocking her speed on the dock, she is moving at 119

Velocity This introduces the contrast between speed and velocity n Velocity is the speed in a particular direction. n It tells us not only “how fast” (like speed) but also how fast in “what direction. ” 120

Velocity, cont’d n In common language, we don’t distinguish between the two. n This sets you up for confusion in a physics class. n During a weather report, you might be given the wind-speed is 15 mph from the west. The speed of the wind is 15 mph. n The wind is blowing in a direction from the west to the east. n So you are actually given the wind velocity. n 121

Velocity: Speed plus Direction n Speed is a “scalar” n No particular direction n Velocity is a “vector” n Speed in a particular direction

Vector addition n Quantities that convey a magnitude and a direction, like velocity, are called vectors. n We represent vectors by an arrow. The arrow represents the direction n The length indicates the magnitude. n 123

Vector addition, cont’d n Consider again the woman running on a ship. n If ship and woman are in the same direction, the vectors add. 124

Vector addition, cont’d n Consider again someone running on a ship. n If ship and woman are in opposite directions, the vectors subtract. 125

Vector addition, cont’d n What if the vectors are at an angle? 126

Vector addition, cont’d n The resulting velocity of the bird (from the bird’s velocity and the wind) is a combination of the magnitude and direction of each velocity. Plane and Wind 127

Vector addition, cont’d n We can find the resulting magnitude of the Pythagorean theorem. a c b 128

Vector addition, cont’d n This is used to find the net speed of the bird. n This is for your information only; it won’t be on a test 6 8 10 129

Vector addition, cont’d n Here are more examples, illustrating that even if the bird flies with the same velocity, the effect of the wind can be constructive or destructive. 130

Vector Addition Resultant Velocity River Boat 131

Vector Addition Vector 3 = Vector 1 + Vector 2 = 300 miles/hour, north Vector 1 = 300 miles/hour, west 132

Vector Addition 133 Vector Addition

Acceleration n Acceleration is the change in velocity divided by the elapsed time. n It measures the rate of change of velocity. n Mathematically, 134 Acceleration vs Constant Velocity

Acceleration, cont’d n The units are n In SI units, we use m/s 2. 135

Gravity is an acceleration g = 9. 8 m/s 2 136 About_Falling_Things

Acceleration, cont’d n A common way to express acceleration is in terms of g’s. n One g is the acceleration an object experiences as it falls near the Earth’s surface: g = 9. 8 m/s 2. n So if you experience 2 g during a collision, your acceleration was 19. 6 m/s 2. 137

Acceleration, cont’d n There is an important point to realize about acceleration: It is the change in velocity. 138

Acceleration, cont’d n Since velocity is speed and direction, there are three ways it can change: change in speed, n change in direction, or n change in both speed & direction. n n The change in direction is an important case often misunderstood. 139

Acceleration, cont’d We know that acceleration takes place as this car speeds. n The change in velocity is Δv = v 2 – v 1 Stoplight Accel 140

Acceleration, cont’d n But acceleration also takes place if you drive through a curve with the cruise control set. Not because your speed changes. n But because your direction is changing. n n You can sense acceleration if items on your dash slide around. (More on this in chapter 2. ) Δv = v 2 – v 1 141

All these motions are Acceleration Hot Wheels

Example 1. 3 A car accelerates from 20 to 25 m/s in 4 seconds as it passes a truck. What is its acceleration? 143

Example 1. 3 ANSWER: The problem gives us The acceleration is: 144

Example 1. 3 CHECK: Does this make sense? The car needs to increase its speed 5 m/s in 4 seconds. If it increased 1 m/s every second, it would only reach 24 m/s. So we should expect an answer slightly more than 1 m/s every second. 145

Example 1. 4 After a race, a runner takes 5 seconds to come to a stop from a speed of 9 m/s. Find her acceleration. v = 9 m/s 146

Example 1. 4 ANSWER: The problem gives us The acceleration is: 147

Example 1. 4 CHECK: Does this make sense? If she was traveling at 10 m/s, reducing her speed 2 m/s every second would stop her in 5 seconds. What’s up with the minus sign? 148

Negative Acceleration Means the Object is Slowing Down Like this car. . . avoiding the cliff 149

Centripetal acceleration n Remember that acceleration can result from a change in the velocity’s direction. n Imagine a car rounding a curve. n The car’s velocity must keep changing toward the center of the curve in order to stay on the road. 150

Centripetal acceleration n Ditto a ball being swung around on a tether. n n The ball’s velocity must keep changing toward the center to stay in the circle This acceleration is perpendicular to the velocity. 151

Centripetal acceleration, cont’d n So there is an acceleration toward the center of the curve. n Centripetal acceleration is the acceleration associated with an object moving in a circular path. n Centripetal means “center-seeking. ” 152

Centripetal acceleration, cont’d n For an object traveling with speed v on a circle of radius r, then its centripetal acceleration is 153

Centripetal acceleration, cont’d n Note that the centripetal acceleration is: n proportional to the speed-squared n inversely proportional to the radius 154

Example 1. 5 Let’s estimate the acceleration of a car as it goes around a curve. The radius of a segment of a typical cloverleaf is 20 meters, and a car might take the curve with a constant speed of 10 m/s. 155

Example 1. 5 ANSWER: The problem gives us The acceleration is: 156

Example Problem 1. 18 An insect sits on the edge of a spinning record that has a radius of 0. 15 m. The insect’s speed is about 0. 5 m/s when the record is turning at 33 -1/3 rpm. What is the insect’s acceleration? 157

Example Problem 1. 18 ANSWER: The problem gives us The acceleration is: 158

Centripetal Acceleration of a peregrine falcon • A peregrine falcon dives vertically at a velocity of 101 m/s. It pulls out of the dive by changing direction at constant velocity over a radius of 61. 2 m. What is the centripetal acceleration of the falcon in m/s 2 and g’s? • a = v 2/r = (101 m/s)2/61. 2 m = 10, 201(m/s)2/61. 2 m = 166. 7 m/s 2 • a = 166. 7 m/s 2 / 9. 8 m/s 2 = 17. 0 g A human would black out before reaching 5 g’s. © Hugh Henry, 2005 159

Types of Motion 160

Simple types of motion — zero velocity n The simplest type of motion is obviously no motion. n The object has no velocity. n So it never moves. n The position of the object, relative to some reference, is constant. 161

Simple types of motion — constant velocity n The next simplest type of motion is uniform motion. n In physics, uniform means constant. n The object’s velocity does not change. n So its position, relative to some reference, is proportional to time. 162

v = 9 m/s Constant Velocity d = vt

Simple types of motion — constant velocity, cont’d n If we plot the object’s distance versus time, we get this graph. n Notice that if we double the time interval, then we double the object’s distance. 164

Simple types of motion — constant velocity, cont’d n The slope of the line gives us the speed. Constant 165 Rt Velocity

Simple types of motion — constant velocity, cont’d n If an object moves faster, then the line has a larger speed. n So the graph has a steeper slope. 166

Reading distance vs time graphs. . . 167

Distance vs Time for Auto with Varying Velocity 168

Simple types of motion — constant acceleration n The next type of motion is uniform acceleration in a straight line. n The acceleration does not change. n So the object’s speed is proportional to the elapsed time. 169

Simple types of motion — constant acceleration, cont’d n A common example is free fall. n Free fall means gravity is the only thing changing an object’s motion. n The speed is: 170

Simple types of motion — constant acceleration, cont’d n If we plot the object’s speed versus time, we get this graph. n Notice that if we double the time interval, then we double the object’s speed. Rt Velocity w/Rt Accel 171

Simple types of motion — constant acceleration, cont’d n The slope of the line is the acceleration: 172

Simple types of motion — constant acceleration, cont’d n For an object starting from rest, v = 0, then the average speed is 173

Simple types of motion — constant acceleration, cont’d n The distance is the average speed multiplied by the elapsed time: 174

Simple types of motion — constant acceleration, cont’d n If we graph the distance versus time, the curve is not a straight line. n The distance is proportional to the square of the time. 175

Distance vs Time for Freely Falling Body 176

For constant acceleration: v = at is a straight line, but 2 d = at /2 is a parabola 177

Non. Constant Acceleration of Gearshift Car 178

Ball Thrown Straight Up Velocity in direction of motion; Acceleration (g) always down 179

Summary of Important Equations 181

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