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Physics 121

Physics 121. 1. Introduction. 1.1 Science and Creativity 1.2 Physics and its relation to other fields 1.3 Models, Theories, and Laws 1.4 Measurement and Uncertainty 1.5 Units, Standards, and the SI System 1.6 Converting Units 1.7 Order of Magnitude: Rapid Estimating

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Physics 121

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  1. Physics 121

  2. 1.Introduction 1.1 Science and Creativity 1.2 Physics and its relation to other fields 1.3 Models, Theories, and Laws 1.4 Measurement and Uncertainty 1.5 Units, Standards, and the SI System 1.6 Converting Units 1.7 Order of Magnitude: Rapid Estimating 1.8 Mathematics in Physics

  3. Example 1.1 . . . Pizza Party ;-) A 6 inch round pizza can comfortably serve one student. How many students can a 12 inch round pizza with the same crust thickness serve?

  4. Linear and Non-Linear Thinking! • Does the braking distance of a car double when you double the speed? • Does a 12 inch pizza serve twice as many people as a 6 inch pizza?

  5. Solution 1.1 . . . Pizza Party ;-) If a 6 inch pizza can comfortably serve one student, then a 12 inch pizza with the same crust thickness will serve a party of 4

  6. Powers of 10 • 1,560 = 1.56x103 • 4,200,000 = 4.2x106 • 103 = 1,000 • 106 = 1,000,000 = 1M = 1 Million • 2.5GB = 2.5x109 = 2.5 Giga Bytes = 2.5 Billion Bytes • 0.007 = 7x10 -3 = 7 parts in a thousand

  7. Sig Figs (Significant Figures) • Measurements in science always entail UNCERTAINTIES. • For example, a measurement of 2.4 cm is likely to be actually between 2.3 and 2.5 cm … you never know! • So our uncertainty is 0.1 cm. In other words, we may express our measurement as 2.40.1

  8. Sig Figs . . . continued! • So you see 2.4 and 2.40 are not the same! 2.4 has 2 sig figs and 2.40 has 3 sig figs. • 2.4 means that the number is probably between 2.3 and 2.5. • On the other hand, 2.40 means that the number is probably between 2.39 and 2.41

  9. Example 1.2 . . . Sig Figs What is the area of a circle whose radius is measured to be 2 .5 cm? A. 19.634954 cm2 B. 19.634954 cm C. 20 cm2 D. 7.8 cm

  10. Hint: Sig Figs Problem . . . • 6.5 has 2 sig figs • 7.28 has 3 sig figs • 65.142 has 5 sig figs • 2.3547681 has 8 sig figs • Unless specified otherwise, in this class we will report our answers using 2 sig figs

  11. Solution 1.2 . . . Sig Figs What is the area of a circle whose radius is measured to be 2 .5 cm? A. 19.634954 cm2 B. 19.634954 cm C. 20 cm2 D. 7.8 cm

  12. SI (metric) Units • 1 meter (m) = 100 cm • 1 kilogram (kg) = 1000 g • 1 kilometer (km) = 1000 m • 1 in. = 2.5 cm • 1 mi. = 1.6 km • 1 kg = 2 pounds • 1 liter (L) = 1000 cm3 • 1 gallon = 4 L

  13. Example 1.3 . . . Unit Conversion Convert 55 mph to km / h and m / s

  14. Solution 1.3 . . . Unit Conversion 55 miles / h x 1.6 km / 1 mi. = 88 km / h 88 km / h x 1000 m / 1 km x 1 h / 3600 s = 24 m /s

  15. That’s all folks!

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