Chapter 1 Introduction to Physics, Measurement, and Estimating

1. Chapter 1 Introduction to Physics, Measurement, and Estimating

2. Zero Gravity Pac-Man

3. Chapter Introduction • The Nature of Science • The Scientific Method • Physics and How it Relates to Other Fields • Models, Theories and Laws • Measurement and Uncertainty • Significant Figures, Scientific Notation • Units, Standards, and the SI System • Unit Conversions

4. 1-1 The Nature of Science Observations and Research Start the Cycle! What did Aristotle and Galileo observe about the nature of horizontal motion? Did they reach the same conclusion?

5. 1-1 The Nature of Science Observation: the first step in the scientific method; requires imagination to tell what is important. Research: Thank goodness for the internet (and other people’s hard work)! Hypothesis: “an educated guess” Experiments are controlled tests carried out to determine if a hypothesis is true or not true. All experiments produce data, which is then analyzed to see if a hypothesis is supported.

6. 1-1 The Nature of Science Conclusion: stateswhether the original hypothesis was supported. After doing all of this hard work your next step is to…REPORT YOUR RESULTS!!! Then the cycle continues. Journals – Where scientists publish their results. http://pubs.acs.org/journal/jacsat Why is this important?

7. 1-1 The Nature of Science The Scientific Method in Action: Galileo and Free Fall http://www.youtube.com/watch?v=_XJcZ-KoL9o

8. 1-1 The Nature of Science • Theories are used to explain observations. • How does a new theory get accepted? • It makes predictions that agree better with data. • The new theory explains a greater range of phenomena (natural occurrences).

9. 1-2 Physics and Its Relation to Other Fields Physics is considered the most basic science; it deals with the behavior and structure of matter. Physicsis needed in both architecture and engineering. Other fields that use physics, and make contributions to it: physiology, zoology, life sciences, chemistry, … Chem Review: What is matter?

10. 1-2 Physics and Its Relation to Other Fields Communication between architects and engineers is essential if disaster is to be avoided. What happens when you don’t do your physics homework…

11. 1-3 Models, Theories, and Laws • Models are used to help people understand phenomena. Care must be taken to know the limits of the model and not take it too seriously. • What are some examples of models? • A theory is detailed and can give testable predictions. • A law is a brief description of how nature behaves. It DOES NOT explain why things happen. • A principle is similar to a law, but applies to a narrower range of phenomena.

12. Summary • Be sure to know the steps of the scientific method: • Make an observation • Research • Make a Hypothesis • Experiment (test your hypothesis) • Collect Data • Analyze Data • Draw a Conclusion (was the hypothesis supported?)

13. Summary • You are expected to know all of the underlined terms in the slides (hint, hint) • Be able to list several different types of models, and what it is that they are helping to explain. • Is physics considered the most basic science? Why? • Theories vs. Laws. Both describe natural events…what is the difference between them?

14. A side note: technology Pure science is merely concerned with gaining knowledge about how the world works. Technology is a direct result of applied science (i.e. knowledge applied to solve a specific problem). Both applied science and pure science can influence one another.

15. A side note: technology

16. 1-4 Measurement and Uncertainty; Significant Figures No measurement is exact; there is always some uncertainty due to limited instrument accuracy and difficulty reading results. What is the smallest unit of measurement that you can use with this ruler?

17. 1-4 Measurement and Uncertainty; Significant Figures Estimated uncertainty is written with a ± sign; for example: Percent uncertainty is the ratio of the uncertainty to the measured value, multiplied by 100: Try it out: What is the percent uncertainty in the following measurement? 5.8 ± 0.5 km

18. 1-4 Measurement and Uncertainty; Significant Figures Accuracy vs. Precision

19. 1-4 Measurement and Uncertainty; Significant Figures • The number of significant figures is the number of reliably known digits in a number. • All nonzero numbers are significant. • Any zero between nonzero #s is significant • Any zero to the right of the decimal point is significant, as long as there is a nonzero number to the left ofthe decimal point. • Any placeholder zeros are not significant. • “Counting Numbers” have an infinite number of significant figures.

20. 1-4 Measurement and Uncertainty; Significant Figures All nonzero numbers are significant. “Counting Numbers” have an infinite number of significant figures.

21. 1-4 Measurement and Uncertainty; Significant Figures Any zero between nonzero numbers is significant

22. 1-4 Measurement and Uncertainty; Significant Figures Any zero to the right of the decimal point is significant, as long as there is a nonzero number to the left ofthe decimal point.

23. 1-4 Measurement and Uncertainty; Significant Figures Any placeholder zeros are not significant.

24. 1-4 Measurement and Uncertainty; Significant Figures How many significant figures does each of the following numbers have? 20.21 cm has ______ significant figures 0.062 cm has ______ significant figures 15,100 cm has ______ significant figures 80 km is ambiguous – it could have 1 or 2 significant figures.

25. 1-4 Measurement and Uncertainty; Significant Figures When adding or subtracting, the answer is no more accurate than the least accurate number used. Example: 189 g + 55.67 g = ______ g

26. 1-4 Measurement and Uncertainty; Significant Figures When multiplying or dividing numbers, the result has as many significant figures as the number used in the calculation with the fewest significant figures. Example: 11.3 cm x 6.8 cm = ______ cm2

27. 1-4 Measurement and Uncertainty; Significant Figures Try it out: how many significant figures are in the following numbers? 5054 0.0037 16000 0.009820 1600 pears Multiply or divide the following, using sig figs. 78.24 x 0.0052 = _________ (33 x 451)/120.5 = _________

28. 1-5 Units, Standards, and the SI System

29. 1-5 Units, Standards, and the SI System We will be working in the SI system, where the basic units are kilograms, meters, and seconds. Other systems cgs; units are grams, centimeters, and seconds. The British engineering system has forceinstead of mass as one of its basic quantities. The units are pounds, feet, and seconds.

30. The SI prefixes between the two arrows are the most common ones seen…be sure to have these memorized!

31. 1-5 Units, Standards, and the SI System Derived units are just combinations of the SI base units seen at the right. Example: Speed and Velocity

32. 1-6 Converting Units Converting between metric units, for example from kg to g, is easy, as all it involves is powers of 10. Converting to and from British units is considerably more work. For example, given that 1 m = 3.28084 ft, this 8611-m mountain is 28251 feet high.

33. Summary of Chapter 1 • Theories are created to explain observations, and then tested based on their predictions. • A model is like an analogy; it is not intended to be a true picture, but just to provide a familiar way of envisioning a quantity. • A theory is much more well-developed, and can make testable predictions; a law is a theory that can be explained simply, and which is widely applicable. • Dimensional analysis is useful for checking calculations.

34. Summary of Chapter 1 • Measurements can never be exact; there is always some uncertainty. It is important to write them, as well as other quantities, with the correct number of significant figures. • The most common system of units in the world is the SI system. • When converting units, check dimensions to see that the conversion has been done properly. • Order-of-magnitude estimates can be very helpful.