Introduction to Physics: Study of Matter, Energy, and Interactions

1. What is Physics? • The study of matter, energy, and the interaction between them •  Physics is about asking fundamental questions and trying to answer them by observing, hypothesizing, experimenting, and communicating • Physics involves the study of the physical world from the largest of scales (e.g. the universe as a whole) to the smallest of scales (e.g. subatomic particles) • Can you be more specific?. See http://www.physics.org/article-questions.asp?id=18

2. What do Physicists Study?

3. How Does Science Work? • Models • A simpler way of representing a complex phenomenon • E.g. physical models, equations, laws, simulations, etc. • Physicists use models to: • Describe phenomena • Build hypotheses • Make predictions

4. Two Types of Science • Basic science involves questions and research about the fundamental nature of the physical world • Applied science involves questions with a view toward solving a problem

5. 1.2 Measurement in Experiments

6. Learning Objectives • List basic SI units and quantities they describe • Convert measurements to scientific notation • Distinguish between accuracy & precision • Use significant figures in measurements & calculations

7. Numbers as Measurements • In science, numbers represent measurements • Numbers involve three things • Magnitude how much? • Dimensions length, mass, time • Units of what?

8. The SI system • The standard measurement system for science • Formerly called the metric system • Base units • Basic units that are not a combination of some other units • Derived units • Are combinations of base units

9. Base Units

10. Derived units • Derived units are combinations of base units

11. Prefixes indicate orders of magnitude (powers of 10)

12. Converting Prefixes & Units • The main idea: multiply the given unit by a conversion factor yielding the desired unit • Conversion factor: a ratio of two units that is an equivalent to 1. • Example: convert millimeters to meters 1 mm x 10-3 m = 1 x 10-3 m 1 mm Practice 1A, #1-5

13. Converting units of area and units of volume • How many cm2 are in 1 m2? • How many cm3 are in 1 m3? • How many in3 are in 1 L? • 1 in = 2.54 cm • 1 L = 103 mL • 1 mL = 1 cm3

14. Scientific Method A way of thinking and problem solving A group of related processes and activities http://www.sciencebuddies.org/science-fair-projects/overview_scientific_method2.gif

15. Scientific Method: Important Terms • Law vs. Theory • Describes vs. explains • Fact & Observation • a scientific fact is an objective and verifiable observation • Hypothesis • Tentative explanation • testable • Experiment • Test of the hypothesis

16. Accuracy & Precision • Accuracy • Nearness of a measurement to the true value • Precision • Degree of exactness or refinement of a measurement • Repeatability of a measurement

17. Precision • describes the limit of exactness of a measuring instrument • Significant figures reflect certainty of a measurement • Are figures that are known because they are measured

18. Significant Figures • Represent measured numbers (numbers known with certainty) and one final estimated digit • Reflect the precision of an instrument • Must be reported properly • Require special handling in calculations

19. Rules to determine significant digits 1. All non-zeros ARE 2. All zeros between non-zeros ARE 3. Zeros in front of non-zeros ARE NOT 4. Final zeros to right of decimal ARE 5. Final zeros without a decimal ARE NOT 6. Final zeros to left of decimal ARE

20. How many significant figures? • 50.3 20.001 • 3.0025 3426 • 0.892 210 • 0.0008 6.58 x 103 • 57.00 1.534 x 10-4 • 2.000000 2.00 x 107 • 1000 5000. • 20. 30

21. Rules of calculating with significant figures • When adding & subtracting, final answer must have fewest decimal placespresent in the calculation. • When multiplying & dividing, final answer must have fewest significant digitspresent in the calculation. • Number of figures in a constant or exact numbers are do not affect calculations involving sig figs.

22. Uncertainty in Measurement • No measurement is correct with 100% precision. • All measurements are approximations • Therefore, all measurements have a degree of uncertainty • This means that measurements should be described with their degree of uncertainty

23. Uncertainty in measurement defines the range in which the true value is found. • Estimated uncertainty • ± one half smallest increment of measurement • E.g. a ruler graduated in 0.1 cm units would be reported as 5.2 ± 0.05 cm • So the true value of the measurement lies between 5.2 - 0.05 and 5.2 - 0.05 cm • The actual value is between 5.15 cm and 5.25 cm

24. Is this diamond yours? • Use estimated uncertainty to answer this question • You have a diamond with a mass of 8.17 grams, measured on a scale with a precision of 0.01 g • You lend the diamond to a friend, who returns it. The returned diamond measures 8.16 g • Assuming the balance is operating properly, is the diamond yours? • Why or why not?

25. Fractional and percent uncertainty • Fractional uncertainty • Helps describe the degree of uncertainty relative to the amount being measured • Is the estimated uncertainty divided by the measurement • In this example it is 0.05/5.2 = .0096 cm • What happens to fractional uncertainty as the magnitude of the measure increases? • Percent uncertainty • = fractional uncertainty x 100 • 0.0096 = 0.96% • Measurement is reported as 5.2 ± 0.96%

26. 1.3 Language of Physics • Mathematics is the language of physics • Data is collected in a table form • Data is graphed to show relationship of independent & dependent variables

27. Data Table and Graph

28. Equations Equations indicate relationships of variables

29. Evaluating Physics Equations • Dimensional analysis can give you clues how to solve a problem • Dimensional analysis can help check many types of problems because… • Dimensions can be treated as algebraic quantities • Example: derive a formula for speed • Example: How long would it take a car to travel 725 km at a speed of 88 km/h?

30. Order of Magnitude Estimates • Physics often uses very large and very small numbers • Using powers of ten as estimates of the numbers can help estimate and check your answers • Example: from the previous problem,

31. Order of Magnitude Estimates • What would be a reasonable order of magnitude estimate for…. • The length of a soccer field in meters? • The mass of a sparrow in kg? • The length of a fly meters? • How much time would it take for a fly to fly from one end of the school building to the other?