Introduction to Physics….

1. Introduction to Physics…. Unit 0: Review of basic science and math skills

2. What is physics? • A branch of science that involves the study of the physical world…. • Energy • Matter • How the two are related • How things work • Make observations • Make predictions • Use mathematics to explain physical observations and model them

3. Math Review…… • Solving for variables….. • In most problems you will be solving for one variable and given information for the other parameters of the problem. • Try this: • 2x + 10 = 44 • Solve for t: v=d/t

4. Significant Figures….. • All digits 1-9 are considered significant • Sandwiched zeros are considered significant. • Zeros at the end of a number with a decimal point are significant. • Try this: • How many sig figs are in the following…. • 100001 102 2. 1.3 • 000001 0.002 0.02 1

5. For tests and class work purposes unless otherwise stated, your answers should be rounded to have 3 significant figures. • Note: read instructions in syllabus for entering answers for online homework.

6. SI Units….Metric System….Measurement • Physics involved working with measurements of many types and each type of quantity must be expressed in the appropriate units or combination of units. • Distance, displacement or length: meter • Mass: kilogram (kg) • Time: second (m) • Electric current: ampere (A) • Temperature: Kelvin (K)

7. Many of the units in physics are Derived units….combinations of 2 or more base units. • Acceleration: m/s/s or m/s2 • Area: m2 • Electric charge: Coulomb (C ) A•s • Energy: Joule (J) kg•m2/s2 • Force: newton (N) kg•m/s2 • Frequency: hertz (Hz) s-1 • Magnetic field: tesla (T) kg/A•s2 • Velocity: m/s • Volume: m3

8. Math and sig figs…. • If adding and subtracting, answers should contain the fewest decimal places as the one with the least decimal places in the set. • If multiplying and dividing, the answer should be expressed in fewest sig figs according to the number with the least in the set.

9. Converting…… • Sometimes it will be necessary to convert from one unit to another in order to solve a problem. This may be within the metric system or between the metric system and English system. • It’s a little harder from English unit to English unit because you have to know the equivalent unit and its often a different name. Ex. Feet to inches, ounces to pounds

10. In the metric system, the base unit for a given quantity stays the same and when you convert you are assigning prefixes that have a set quantity. • Kilo-1000 • Milli- 0.001 • Example: grams to kilograms, meters to kilometers • Everything in the metric system is based on 10.

11. Metric Practice….. • G = F/B where B is measured in meters and F is measured in Newtons. What are the units of G? If G = B2F? If G = B-F If G = F3 K B

12. Practice on your own… • The force of a magnetic field on a charged, moving particle is given by F= Bqv, where F is the force in kg•m/s/s, q is the charge in A•s, and v is the speed in m/s. B is the strength of the magnetic field, measured in teslas, T. What is 1 tesla described in base units?

13. A proton with charge 1.60 x 10e-19 A•s is moving at 2.4 x 10e5 m/s through a magnetic field of 4.5 T. You want to find the force on the proton.

14. Dimensional Analysis….converting • Conversion factor: an equivalent value that lets you convert between units • Common equivalents • 1 inch = 2.54 cm • 1 mile = 1.61 km • 1 kg = 2.21 lbs • 1 lb = 4.45 N • 1 cal = 4.184 J • See page 911 in appendix D for more.

15. Convert….. • Mad King Henry……… • Helps you remember order of prefixes from smallest to largest • Can also move the decimal • Large to small---move decimal to left • Small to large – move decimal to the right • This works when you are doing Metric Conversions but not with English to metric or English to English.

16. How many seconds are in a leap year? • How many miles in a 2 kilometers? • Convert 43 km/h to m/s.

17. Convert the speed 5.30 m/s to km/h. • Convert 2 minutes to seconds.

18. Scientific Method…. • Gather background information • Form hypothesis or question to be answered. • Perform experiments/tests to collect data. • Organize data. • Analyze data. • Conclusions. • Re-test.

19. Taking measurements…. • Experiments in physics usually involve taking measurements. • A measurement is simply a comparison between an unknown quantity and a standard. • Measurements be accurate and precise. • Accuracy: how well the results of a measurement agree with the real value or the accepted value as measured by competent experimenters. • For instruments, calibration against a standard is necessary to insure the validity of the measurements. • Precision: degree of exactness; how close your measurements are to each other • Significant figures in a measurement show its precision. A measure of 67.100g is precise to the nearest thousandth of a gram. • The number of significant figures in a measurement is also dependent upon the instrument used to measure.

20. Data……. • Many investigations in physics involve data collection and organization. Often scientists organize data using charts and graphs or diagram. • One way to visualize or display data involving motion is to use graphs to show information from strobe pictures.

21. S T R O B E P I c s O sec 5 sec 10 sec 15 sec

22. Meterstick and Disc Activity • Read your activity sheet. • Obtain the materials from your teacher. • Follow instructions carefully.

23. Variables…… • Variable: any factor that might affect the behavior of an experimental setup. • Independent variable: the factor that is changed or manipulated during the experiment. • Dependent variable: the factor that depends on the independent variable

24. In an experiment, the length of a spring is tested using different masses. • Construct a data table to represent this experiment. • Collect data using a spring and 5 different masses. • Graph your data. Draw a line of best fit. • Identify the independent and dependent variables.

25. Linear relationships: y=mx+b • The line of best fit is a straight line • The dependent variable varies linearly with the independent variable • Slope: ratio of the vertical change to the horizontal change • Slope = rise /run or ∆y/∆x • Nonlinear relationships: • Quadratic: y=ax2 + bx + c (parabolic) • One variable depends on the square of another • Inverse: y=a/x one variable depends on the inverse of the other (a hyperbole)

26. Back to the strobe pics….. • Strobe pictures can be used to represent motion. • We can take the information from a series of strobe pictures and graph the data to show the relationship. • You will need to establish an origin and a scale. • Origin: beginning point • Scale: units of measure, increments of measure

27. S T R O B E P I c s O sec 5 sec 10 sec 15 sec

28. Now graph it. Distance (m) 5 10 15 20 0 Time (seconds)

29. Motion at a constant rate Time = 0 s Figure 5 Time = 5 s Figure 6 Time = 10 s Figure 7 Time = 15 s Figure 8

30. Instead of drawing the picture over and over … Figure 9 t=0 sec t= 5 sec t=10 sec t= 15 sec

31. Now graph it. Distance (m) 5 10 15 20 0 Time (seconds)

32. To wrap up: • Mathematics is an important part of a physics class. It is important to practice problems and ask questions in class. • Often you will have to convert units so a good understanding of metric units is essential to success. • Representing data is key to disseminating information about experiments. Data tables should have correct headings with units and a title. Graphs should have a title, labels on the x and y axis with correct units and data points indicated. Best fit lines should be drawn.

33. Accuracy and precision are vital to ensure validity of data. Results should be reproducible. • Assignment: math review set---come prepared for questions and Quiz. • Ticket out the door: • One thing I learned……. • One thing I have a question about……