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## Introduction and Kinematics

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**Introduction and Kinematics**Physics Unit 1 Chapters 1 - 3**Introduction**Physics Chapter 1**1.1 Physics: An Introduction**• Physics studies anything that can be sensed with our five senses. • Starting point of any technology • Car • Planes • GPS • Computers • Cell phones**1.1 Physics: An Introduction**• Model, Theory, Law • Model • A representation of something that is often too difficult (or impossible) to display directly. • It is only accurate under limited situations. • Theory • an explanation for patterns in nature that is supported by scientific evidence and verified multiple times by various groups of researchers. • Law • Uses concise language to describe a generalized pattern in nature that is supported by scientific evidence and repeated experiments. • Often, a law can be expressed in the form of a single mathematical equation.**1.1 Physics: An Introduction**• Scientific Method • Can be used to solve many types of problems, not just science • Usually begins with observation and question about the phenomenon to be studied • Next preliminary research is done and hypothesis is developed • Then experiments are performed to test the hypothesis • Finally the tests are analyzed and a conclusion is drawn**1.1 Physics: An Introduction**• Classical Physics • Organized and finalized in Renaissance • Good model for • objects moving less than 1% the speed of light and only experiencing weak gravitational fields • objects that are big enough to be seen in microscope and larger • Modern Physics • Relativity • Objects moving fast or experiencing large gravitational fields • Quantum • Submicroscopic objects**1.2 Physical quantities and units**• Units • USA uses English system as was used by the British Empire • Rest of world uses SI system (International System or Metric System) • Fundamental Units - Can only be defined by procedure to measure them • Time = second (s) • Distance = meter (m) • Mass = kilogram (kg) • Electric Current = ampere (A) • All other units are combinations of these 4**1.2 Physical quantities and units**• Metric Prefixes • SI system based on powers of ten • Memorize from T to p**1.2 Physical quantities and units**• Unit conversions • Multiply by conversion factors so that the unwanted unit cancels out • Convert 20 Gm to m**1.2 Physical quantities and units**• Convert 15 cg to kg**1.2 Physical quantities and units**• Convert 25 km/h to m/s**Day 2 Homework**• 2) 120 km/h, faster • 3) 3.6 km/h • 4) 91.4 m • 5) 377 ft long, 4530 in • 7) 8.847 km • 8) 1230 km/h • Let me introduce you to my friend … homework. • 1P1-5, 7-8 • Read 1.3-1.4 • 1CQ11 • Answers to Problems • 1) 27.8 m/s, 62 mi/h**1.3 Accuracy, Precision, and Significant Figures**• Accuracy is how close a measurement is to the correct value for that measurement. • Precision of a measurement system is refers to how close the agreement is between repeated measurements.**1.3 Accuracy, Precision, and Significant Figures**Accurate but not precise Precise but not accurate**1.3 Accuracy, Precision, and Significant Figures**• The accuracy and precision of a measuring system leads to uncertainty. • Think of length • 450 cm ± 5 cm • The ± 5 cm is the uncertainty • Where is uncertainty in a measurement and is the measurement**1.3 Accuracy, Precision, and Significant Figures**• If you combine two or more of the same measurements with addition or subtraction, the % uncertainty remains the same • If you combine two or more of the measurements with multiplication or division, the % uncertainty is the sum of the % uncertainties of the individual measurements**1.3 Accuracy, Precision, and Significant Figures**• Significant Figures • Used to reflect uncertainty in measurements • Each measuring device can only measure so accurately • The last digit is always an estimate**1.3 Accuracy, Precision, and Significant Figures**• To find significant figures • Ignore placeholder zeros between the decimal point and the first nonzero digit • Count the number of other digits • 0.000000602 • 3 sig figs • 1032000 • 4 sig figs • 1.023 • 4 sig figs**1.3 Accuracy, Precision, and Significant Figures**• Rules for combining significant figures • Addition or subtraction • The answer can contain no more decimal places than the least precise measurement. • Multiplication or division • The result should have the same number of significant figures as the quantity having the least significant figures entering into the calculation. • I will accept 3 significant figures for all problems in future assignments.**Day 3 Homework**• 14) 4 % • 17) 3, 3, 3 • 18) 2, 3 at most; 1.0 %, 1.00% if all zeros are significant; percent uncertainties • 19) 2.2 %, 59 to 61 km/h • 20) 2 %, 1 mmHg • 21) beats/min • 25) • 27) 12.06±0.04 m2 • Strive for both precision and accuracy on these problems • 1P11-14, 17-21, 25, 27 • Read 2.1-2.2 • 2CQ1-7 • Answers • 11) 2 kg • 12) • 13) 85.5 to 94.5 km/h, 53.1 to 58.7 mi/h**Kinematics**Physics Chapter 2**2.1 Displacement**• Kinematics studies motion without thinking about its cause • Position • Must be able to measure the position of something before you can describe motion • Position is relative to a reference frame • Earth is the most common reference frame, but it could be something else**2.1 Displacement**• Displacement • Change in position relative to a reference frame • Has direction and magnitude • Only depends on final and initial position**2.1 Displacement**• Distance • Total length of the path taken • Only has size**2.1 Displacement**• You drive 20 km east, then turn around and drive 15 km west. What is your displacement? • 5 km east of your starting point • What is your distance?**2.2 Vectors, Scalars, and Coordinate Systems**• Vector • Quantity with direction and magnitude • Can be represented by arrows • Displacement • Scalar • Quantity with only magnitude • Distance**2.2 Vectors, Scalars, and Coordinate Systems**• All vectors and scalar measurements of movement are based on a coordinate system • We’ll usually use**Day 4 Homework**• 3) 13 m, 9 m, 9 m • 4) 8 m, 4 m, -4 m • Displace some lead on your paper • 2P1-4 • Read 2.3-2.4 • 2CQ9-12, 14-17 • Answers • 1) 7 m, 7 m, 7 m • 2) 5 m, 5 m, -5 m**2.3 Time, Velocity, and Speed**• Change in time • Often is 0, so**2.3 Time, Velocity, and Speed**• Velocity • Displacement / time taken • Rate of change of position • Average velocity • The smaller the time interval, the closer it is to instantaneous velocity • Vector • Unit:**2.3 Time, Velocity, and Speed**• Speed • Total Distance / time taken • Scalar • Unit:**2.3 Time, Velocity, and Speed**• The little kid ran 35 m, then turned and ran 15 m back. If he started running at 1:05:00 and ended at 1:06:10, what was his average speed? • Average velocity?**2.4 Acceleration**• Acceleration • Rate of change of velocity • Vector • Unit: • If the acceleration is same direction as motion, then the object is increasing speed.**2.4 Acceleration**• A racecar traveling at 320 km/h hits a barrier and stops in 2 s. What was the average acceleration? (Don’t forget to convert to m/s!)**Day 5 Homework**• 11) 40.0 km/h, 34.3 @ 25° S of E, 3.20 km/h • 13) 384000 km • 14) 6.00 m/s, -1.71 m/s, 4.04 m/s; 3.49 m/s • 16) 4.29 m/s2 • 17) 56.4 m/s2, 5.76 g; -201 m/s2, 20.6 g • 18) 1.43 s, -2.50 m/s2 • 19) 108 m/s2, 11.1 g • Time is important, work efficiently • 2P7-11, 13-14, 16-19 • Read 2.5-2.6 • 2CQ18-19 • Answers • 7) • 8) • 9) 124.88 km/h, 34.689 m/s • 10)**2.5 Motion Equations for Constant Acceleration in One**Dimension • Assume , so and acceleration is constant • and**2.5 Motion Equations for Constant Acceleration in One**Dimension**2.5 Motion Equations for Constant Acceleration in One**Dimension**2.5 Motion Equations for Constant Acceleration in One**Dimension**2.5 Motion Equations for Constant Acceleration in One**Dimension**2.6 Problem-Solving Basics for One-Dimensional Kinematics**• Examine the situation to determine which physical principles are involved. • Maybe draw a picture • Make a list of what is given or can be inferred from the problem. • Identify exactly what needs to be determined in the problem. • Find an equation or set of equations that can help you solve the problem. • Substitute the knowns along with their units into the appropriate equation, and Solve • Check the answer to see if it is reasonable: Does it make sense?**2.6 Problem-Solving Basics for One-Dimensional Kinematics**• A plane starting from rest accelerates to in . How far did the plane travel during this time? • and**2.6 Problem-Solving Basics for One-Dimensional Kinematics**• To avoid an accident, a car decelerates at for and covers of road. What was the car’s initial velocity? • , , , ,**Day 6 homework**• 23) 16.5 s, 13.5 s, -2.68 m/s2 • 24) 173 m, 28.8 m/s • 25) 20.0 m, -1.00 m/s, she’ll be running backwards • 26) 0.120 s, Yes • 27) 0.799 m • 28) 6.87 m/s2, 52.3 m • 29) 28.0 m/s, 50.9 s, 7.68×103 m, 713 m • 30) 7.69×10-3 s • Practice problem solving by solving problems • 2P21-30 • Read 2.7 • 2CQ21-23 • Answers • 21) 38.9 m/s • 22) 502 m/s**2.7 Falling Objects**• In a vacuum all objects fall at same acceleration • Watch Apollo video • Real life • Air resistance**2.7 Falling Objects**• You drop a coin from the top of a hundred story building (1000 m). If you ignore air resistance, how fast will it be falling right before it hits the ground?**2.7 Falling Objects**• How long does it take to hit the ground?**2.7 Falling Objects**• A baseball is hit straight up into the air. If the initial velocity was 20 m/s, how high will the ball go?**2.7 Falling Objects**• How long will it be until the catcher catches the ball at the same height it was hit? • or**2.7 Falling Objects**• How fast is it going when catcher catches it? • so