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AP Physics 1

AP Physics 1. Agenda for Today. Course Introduction General Announcements Structure of the course Scope of the course Begin chapter 1 Course Homepage: http://physicsgbhs.weebly.com/. General Announcements. Assignments : Etkina College Physics AP Edition

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AP Physics 1

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  1. AP Physics 1 Agenda for Today • Course Introduction • General Announcements • Structure of the course • Scope of the course • Begin chapter 1 Course Homepage: http://physicsgbhs.weebly.com/

  2. General Announcements • Assignments: • Etkina College Physics AP Edition • Reading Assignments: Guys and Gals you got to do it. • Homework will do as Indicated on the Website and on the Board each day. • Lectures: (the PowerPoint component) will be posted at the course website • Videos:Selected YouTube videos will be available on line to help with learning the topics

  3. Grading • Several components: • Assessments 45% • Tests,Projects • Practice 20% • Homework, Classwork, • Small Projects • Quizzes/Labs 35%

  4. Course Objectives • To begin to understand basic principles (e.g. Newton's Laws) and their consequences (e.g. conservation of momentum, etc.) • To solve problems using both quantitative and qualitative applications of these physical principles • To develop an intuition of the physical world

  5. Scope of AP Physics • Classical Mechanics: • Mechanics: How and why things work. Motion (dynamics), balance (statics), energy, vibrations, some thermodynamics Classical: • Not too fast (v << c), c ≡ speed of light • Not too small (d >> atom), atoms  10-9 m • Most everyday situations can be described in these terms. • Path of baseball (or a ping pong ball) • Path of rubber ball bouncing against a wall • Vibrations of an elastic string (Vibration Demo) (These reflect Newton’s Laws and forces) • Properties of matter; a roll of the dice (Thermodynamics)

  6. This Week • Position and Time (Chapter 1) • What is Physics • Scientific Method • Vectors • Scientific Notation • Systems of units • Dimensional Analysis • Significant digits

  7. Physics can also be described as the science of motion. What is Physics…..

  8. Metric System • Fundamental or Base Unit: – a standard; a specific quantity – only seven (7) needed to describe all of nature

  9. Metric System • To convert between SI units, multiply or divide by the appropriate power of 10. • Prefixes are used to change SI units by powers of 10, as shown in the table below.

  10. Conversion Between Units • Choose a conversion factor that will make the units cancel, leaving the answer in the correct units. • For example, to convert 1.34 kg of iron ore to grams, do as shown below:

  11. Scientific Notation • Physicists like to measure the very big, the very small and everything in between. • Earth is about 149,000,000,000meters from the Sun. • Scientific notation expresses a quantity as a numbertimes a power of 10. • 1.49×1011 meters = • 14.9×1010 meters = • .149×1012 meters …. which is correct? • Power Of 10 Movie

  12. Standard Scientific Notation: A. Moving the decimal point to left exponent is ___________ number is _____ 1 5 positive 616000 = 6.16 x 10 left Shift ______ to here by ___ places > implied ________ decimal pt. 5 B. Moving the decimal point to right exponent is ___________ number is _____ 1 -3 0.0070 = 7.0 x 10 negative right Shift ______ to here by ___ places < 3

  13. Convert to standard scientific notation 4.3 x 104 2.90 x 10-2 2.012 x 103 5 x 10-1 8 x 101 8.0 x 101

  14. Measurements • We measure things to know something about them; to describe, to understand • Measurements must be accurate and mean the same to all • include 3 pieces of information – magnitude (how much) – units – uncertainty

  15. Measurement • • Precision: • Precision of a measurement is how closely a number of measurements of the same quantity agree with each other. • The precision of a number is limited by random errors • Limited by the smallest division on the measurement scale • Precision describes how close several measurements are to each other. The closer measured values are to each other, the higher their precision.

  16. Measurement • Significant digits (sig figs) • Include all the numbers that can be read directly from the instrument scale plus one doubtful or estimated number. • Reflect the precisionof the measurement. • Significant digits are considered only when calculating with measurements. • There is NO uncertainty with counting or exact conversions.

  17. Figures (numbers) are significant if they are: • Non-Zero numbers: 1, 2, 3, 4, 5, 6, 7, 8, 9 • Any zeros that are: a. between any significant numbers: 509 or 5.009 b. between a non-zero number and the decimal point : 10. c. which are BOTHto the right of the decimal and at the end of a number are ALWAYS significantEx 0.7000(4 sig figs or 4.0900(5 sig figs) NOTE: 0.00007 only 1 sig fig zeros are to the left of the number NOTE: We use scientific Notation to help out with sig figs!!!! Ex: 5 2 4 3 1 1 2 2

  18. 6 1 2 4 3 5 Ex 1: Measure the length of a box: L 4.7 cm = 4.7 ± 0.1 cm L = last digit is _____________ estimated

  19. 6 1 2 4 3 5 Ex 2: Use a “better” ruler: L 0.01 cm = 4.67 ± L = 4.67 cm last digit is ______________ estimated

  20. Sig. figs. when multiplying or dividing: answer has the _________ number of sig. figs., in this case: ____ 3 ____ sig. figs. lower 3.73 x 5.7 = 21 2 ____ sig. figs. 2 Sig. figs. when adding or subtracting: 3 18.541 +106.6 125.1 • ___ decimal places • ___ decimal places 1 lower answer has the _________ number of ___________________ , in this case: ____ decimal places 1

  21. Measurement • Accuracy: (closeness to a standard) Accuracy describes how close a measurement is to a known or accepted value. Suppose, for example, the mass of a sample is known to be 5.85 grams. A measurement of 5.81 grams would be more accurate than a measurement of 6.05 grams.

  22. Measurement • Measurements can be precise even if they are not accurate. • Consider again a sample with a known mass of 5.85 grams. • Suppose several students each measure the sample's mass, and all of the measurements are close to 8.5 grams. • The measurements are precise because they are close to each other • HOWEVER: none of the measurements are accurate because they are all far from the known mass of the sample.

  23. Types of Errors • Systematic Errors • Occur when there is a flaw in the procedure, observer bias, an incorrect assumption, or a flaw with an instrument used to take the measurement (calibration error) • Example 1: Measure the period of a pendulum with a stop watch that is running slow. All results will be shorter that they should be. Tough to estimate this error. • Example 2: Measuring acceleration of a car on a tack and you assume no friction. Acceleration will be less than the theoretical acceleration. • Systematic errors always shift the results one direction • Avoiding systematic errors depends on the skill of the observer to detect them and to prevent or correct them.

  24. Types of Errors • Experimental Error • Errors Due to improperly performing the experiment • Effects both the accuracy and precision of data. • Random Error • Errors that can not be predicted. • Include errors of judgment in reading a meter or a scale and errors due to fluctuating experimental conditions. • Example: Suppose you are making temperature measurements in a classroom over a period of several days. Large variations in the classroom temperature could result in random errors when measuring the experimental temperature changes. • Note: If the random errors in an experiment are small, the experiment is said to be precise. • The effect of random errors can be reduced and minimized by improving and refining experimental techniques, and by repeating the measurement a sufficient number of times so that the erroneous readings become statistically insignificant.

  25. Statistics and Physics • 1. Percent Error: • 2. Percent Difference:

  26. Graphs • Graphs should include the following items. • Labels on each axis, including units • Each axis will contain a scale and evenly-spaced tick marks • A meaningful Title • The Graph should fill the space given for it. If you are doing a graph for a lab or test you should fill the grid provided to you. • DO NOT LEAVE EXTRA SPACE. PLAN AHEAD DECIDE THE UPPER LIMITS OF THE GRAPH FOR EACH AXIS THEN DECIDE ON THE APPORPRIATE INTERVALS!!! • BE NEAT!!!!

  27. Graphs • We vary rarely use x and y as our axis in this class like you do in math. Physics is the real thing not a example like a math homework problem. THIS CLASS ACTUALLY USES THE CONCPETS YOU HAVE LEARNED IN THE MATH YOU HAVE BEEN TAKING FOR YEARS!!!!!!!! • NOTE: Sometimes we put the dependent value (y in math) on the horizontal axis…We do this in physics because its easier to graph and see relationships when linearizing…BE READY TO DO THIS AND UNDERSTAND WHEN IT HAPPENS!!!!!!

  28. Graphs • Regression Analysis (Curve fitting/line of best fit) • We are going to plot our data points…a lot • It ain’t going to look pretty so we use a graphing calculator, computer, or our eye to find the line of best fit so we can determine the model/equation (linear, quadratic, exponential) that best fits our data • If we use the calculator or computer we will use the coefficient of determination (r2 in stat calc) to determine how good our data was (precision and accurately). • Finally, when we conduct analysis of our data we will use the line of best fit/model/equation NOT THE DATA POINTS USED TO DETERMINE THE line of best fit/model/equation

  29. Graphs • Linearizing Graphs • We like to look at graphs that have straight lines (y=mx+b). WHY: Its easy to analyze and its easiest to graph • Therefore in this class we are going to linearize our line of best fit if it does not look like a line (for ex: quadratics, exponentials) In other words no matter what we graph we are going to make it look like a linear line of best fit!!! • How do we do this!!!!

  30. Graphs • Linearizing Graphs • Step 1: Must determine the relationship between the independent and dependent variables • For example: lets say we have a position vs time graph for a falling object and our line of best fit shows us the relationship between position and time is • x= ½ at2 (not a line) • Step 2: To linearize we compare the above equation to the slope intercept form of a linear equation y=mx+ b. We then substitute the variables into line equations as shown below: • x= ½ at2 • y=mx+b • Linearized formula would be • x=ma2+b

  31. Laboratory Analysis and Errors Lab Scientific Method A step by step process where a scientist investigates a question by observing and performing experiments. Step 1 -  State the problem or pose a question Step 2 - Gather information Step 3 - Form a hypothesis                            --  a possible explanation or answer

  32. Step 4 - Test the hypothesis with an experiment Experiments have 2 variables • Independent variable - what you change                                 • Responding variable (dependent) - what you measure • A control is something you do nothing to, used to compare your results

  33. Step 5 - Conclusion Organize data into charts or graphs that can be read by others Step 6 - Draw Conclusions                   Determine if hypothesis is supported or rejected • If hypothesis is not supported - modify hypothesis • If hypothesis is supported - repeat experiment

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