College Physics （大学物理）

1. College Physics（大学物理） Qingxu Li (李清旭) Tel: 62471347, Email: liqx@cqupt.edu.cn Room 306, College of Mathematics and Physics

2. “The most incomprehensible thing about the universe is that it is comprehensible.” — Albert Einstein

3. College Physics • Textbook Physics for Scientists and Engineers with Modern Physics (3rd Ed.), by D. C. Giancoli; 滕小瑛改编, 高等教育出版社 • Reference Books Feynman’ Lectures on Physics, by R. P. Feynman 物理学, 第五版, 马文蔚改编, 高等教育出版社 • Grades Final Exam (70%) + Performance (30%) • Notes a. Exercises and Exam are to be finished in English b. Useful materials can be found in the site slxy.cqupt.edu.cn

4. Contents to be Discussed • Classical /Newtonian Mechanics (28 Periods) • Wave/Physical Optics (20 Periods) • Electromagnetism • Introduction to Modern Physics Relativity, Quantum Physics, etc. (Chp. 15-18, 23-24, 36-40 will not be discussed in the course)

5. The Nature of Sciences (Physics) Observations  Experiments Explanations Theories Verifications Testing Up to date: A theory cannot be absolutely verified! Three ways to unknown: Expt., Theor., Comput.

6. Models and Theories （模型和理论） Model A model is an analogy or mental image of the phenomena in terms of something we are familiar with. A model gives us an approximatemental or visual image for what actually is happening. In simple, a model is a simplified substitute for the real problem that allow us to solve the problem in a relatively simple way. A theory is broader and more detailed than a model, and it attempts to solve a set of problems with great precision. Models often lead to important theories. It is important to tell the differences between the models or theories and the real systems or the phenomena themselves.

7. Physical Laws （物理定律） Laws or physical laws are concise but general statements about how nature behaves, and some- times the statement takes the form of a relationship or equation between quantities. Scientific laws are descriptive: they do NOT say How nature shouldbehave, but rather are meant to describe how nature does behave. Laws are also can not be tested in the infinite variety of cases.

8. Measurement and Uncertainty （测量及其误差） Experiments and therefore measurements play an essential role in physics. Accurate measurement are undoubtedly important, but no measurement is absolutely precise. There is always an uncertainty associated with every measure -ment. (accuracy and precision, P3)

9. Significant Figures （有效数字） In general, a significant figure in a measurement is a reliably known digit. You SHOULD avoid the temptation to keep more digits in the final answer than is justified. When multiplying several quantities, the number of significant figures in the final answer is the same as the number of significant figures in the quantity having the lowest number of significant figures. The same rule applies to division. When numbers are added or subtracted, the number of decimal places in the result should equal to the smallest number of decimal places of any term in the sum. the number of decimal places 小数点后的位数

10. However, to obtain the most accurate result, you should normally keep an extra significant figure or two throughout a calculation, and round off only in the final result. General rule for rounding off numbers: the last digit retained is to be increased by 1 if the last digit dropped is greater than 5. If the last digit dropped is less than 5, the last digit retained remains unchanged. If the last digit dropped is equal to 5, the remaining digit should be rounded to the nearest even number.

11. Scientific Notion Numbers are commonly written in “powers of ten”, or “scientific notion”. One advantage of scientific notion is that it allows the number of significant figures to be clearly expressed.

12. Standards of Length, Mass, and Time (SI system, Système International) Length, meter （长度，米） The meter: the distance traveled by light in a vacuum during a time of 1/299792458 second. Mass, kilogram （质量，千克） The kilogram: the mass of a specific platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures at Sevres, France. Time, second （时间，秒） The second: 9192631770 times the period of oscillation of radiation from the cesium atom. (P5, Table 1-1, 1-2, 1-3, 1-4, 1-5)

13. Estimates and Order-of-Magnitude Calculations （估算和数量级计算） Order-of-Magnitude is valuable when little information is available and an approximate answer is useful. order-of-magnitude a certain quantity as the power of ten of the number that describe that quantity For an order-of-magnitude calculation, the results are reliable to within about a factor of 10. Example 1-4, 1-5.

14. Dimensional Analysis （量纲分析） Dimension denotes the physical nature of a quantity Dimensions of length, mass, and time: L, M, and T. Dimensions can be treated as algebraic quantities Quantities can be added or subtracted only if they have the same dimensions. An arbitrary equation holds, if and only if the dimensions on the two sides of the equation. Principles of Physics, Serway and Jewett.

15. P44 3-1---3-5 Vector （矢量） A vector is specified by both magnitude and direction. magnitude 大小，数量，震级 direction 方向 module 模 unit vector 单位矢量

16. Properties of Vector equality addition subtraction multiplication of a vector by a scalar addition: the triangle method of addition or parallelogram rule of addition （矢量求和：三角形法则或者平行四边形法则） equality 相等，addition 加法，subtraction 减法，multiplication 乘法

18. Scalar Vs Vector （矢量和标量） path Vs displacement vector Fig. 1.1 As a particle moves from A to B along an arbitrary path represented by the broken line, its displacement is a vector quantity shown by the arrow draw from A to B. path 路程 displacement 位移

19. Problems P13: 8, 23, 38 P69: 12,15 This PPT file can be downloaded from the website: slxy.cqupt.edu.cn