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Introduction and Kinematics

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  1. Introduction and Kinematics Physics Unit 1 Chapters 1 - 3

  2. Introduction Physics Chapter 1

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 1.2 Physical quantities and units • Metric Prefixes • SI system based on powers of ten • Memorize from T to p

  9. 1.2 Physical quantities and units • Unit conversions • Multiply by conversion factors so that the unwanted unit cancels out • Convert 20 Gm to m

  10. 1.2 Physical quantities and units • Convert 15 cg to kg

  11. 1.2 Physical quantities and units • Convert 25 km/h to m/s

  12. 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

  13. 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.

  14. 1.3 Accuracy, Precision, and Significant Figures Accurate but not precise Precise but not accurate

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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

  21. Kinematics Physics Chapter 2

  22. 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

  23. 2.1 Displacement • Displacement • Change in position relative to a reference frame • Has direction and magnitude • Only depends on final and initial position

  24. 2.1 Displacement • Distance • Total length of the path taken • Only has size

  25. 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?

  26. 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

  27. 2.2 Vectors, Scalars, and Coordinate Systems • All vectors and scalar measurements of movement are based on a coordinate system • We’ll usually use

  28. 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

  29. 2.3 Time, Velocity, and Speed • Change in time • Often is 0, so

  30. 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:

  31. 2.3 Time, Velocity, and Speed • Speed • Total Distance / time taken • Scalar • Unit:

  32. 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?

  33. 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.

  34. 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!)

  35. 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)

  36. 2.5 Motion Equations for Constant Acceleration in One Dimension • Assume , so and acceleration is constant • and

  37. 2.5 Motion Equations for Constant Acceleration in One Dimension

  38. 2.5 Motion Equations for Constant Acceleration in One Dimension

  39. 2.5 Motion Equations for Constant Acceleration in One Dimension

  40. 2.5 Motion Equations for Constant Acceleration in One Dimension

  41. 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?

  42. 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

  43. 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? • , , , ,

  44. 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

  45. 2.7 Falling Objects • In a vacuum all objects fall at same acceleration • Watch Apollo video • Real life • Air resistance

  46. 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?

  47. 2.7 Falling Objects • How long does it take to hit the ground?

  48. 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?

  49. 2.7 Falling Objects • How long will it be until the catcher catches the ball at the same height it was hit? • or

  50. 2.7 Falling Objects • How fast is it going when catcher catches it? • so