Chapter 1: Introduction to Physics, Unit Conversions, and an Introduciton toVectors

1. Chapter 1: Introduction to Physics,Unit Conversions,and an IntroducitontoVectors If you can’t explain it simply, you don’t understand it well enough. -Albert Einstein If you thought science was certain – well, that is just an error on your part. -Richard Feynman

2. What is Physics? • It is the study of the basic nature of matter and the interactions that govern its behavior. • It is the MOST fundamental of the sciences. • Its principles and theories can be used to explain the fundamental interactions involved in chemistry, biology, and other sciences at the atomic and molecular level.

3. Steps in the Scientific Method • Careful observations of natural phenomena • Formulations of rules or empirical laws based on generalizations from these observations and experiences • Development of hypotheses to explain the observations and empirical laws and the refinement of those hypotheses into theories • Testing of hypotheses or theories by further experimentation or observation

4. Units • SI (Le SystemeInternationaled’Unites) units are used in the scientific community in the United States • This is otherwise known as MKS units (meters, kilograms, seconds) • Length is given in meters (One meter is the distance traveled by light in a vacuum during 1/299,792,458 of a second, this is the equivalent of defining the speed of light as 299,792,458) • Mass is given in kilograms (One kilogram is the mass of the international standard kilogram, a polished platinum-iridium cylinder stored in Paris) • Time is given in seconds (One second is the time required for 9,192,631,770 oscillations of the radio wave absorbed by the cesium-133 atom)

5. Prefixes

6. Unit Conversions Multiplying expressions by one does not change its value. Similarly, a conversion of 2 feet to meters would be

7. Significant Figures • To state our knowledge of a particular number precisely, we use significant figures: Example: 0.00620 = 6.20 x 10-3 Notes: • The leading three zeros locate the decimal point, but are not significant in and of themselves. • The number of significant figures does not equal the number of decimal points. • Changing units shifts the decimal point but does not change the number of significant figures.

8. Using Sig Figs • When multiplying or dividing several numbers, or taking roots, the number off significant figures in the answer should match the number of significant figures of the least precisely known number used in the calculation. • When adding or subtracting several numbers, the number of decimal places in the answer should match the smallest number of decimal places of any number used in the calculations. • Exceptions: • It is customary to keep one extra significant figure if (and only if) the number starts with a 1. • It is acceptable to keep one or two extra digits during intermediate steps of a calculation, as long as the final answer is reported with the proper number of significant figures. Textbook problems in science and engineering use an accepted standard of three significant figures for nearly all calculations. Use scientific notation in your calculators at all times.

9. Question 1:Convert the following to SI units: • 9.12 μs • 3.42 km • 44 cm/ms • 80 km/hour

10. Question 2:Convert the following to SI units: • 1 hour • 1 day • 1 year • 32 ft/s2

11. Question 3:The quantity called mass density is the mass per unit volume of a substance. Express the following mass densities in SI units: • Aluminum, 2.7 x 10-3 kg/cm3 • Alcohol, 0.81 g/cm3