Physics I Wu Hao 1

Why learning physics “ Physics is the most fundamental and all-inclusive of the science, and has had a profound effect on all scientific development.” —— Richard Feynman 1) Understanding our world 2) Necessary base knowledge 3) Scientific thinking methods 4) Physics in everyday life 2

Water of pool Example1: It need 4 hours to fill a pool, 3 hours to empty, how about both switch is turned on? Is water flow constant? dm comes out in dt h 3

About the course grade 30% for the midterm, 40% for the final exam, 30% for the attendance, homework, quiz, project and so on. 4

Textbook and reference book Focus on those mentioned in class Notice: remember specialized vocabulary Reference books ： 《 The Feynman Lectures on Physics 》, Feynman etc ， World Publishing Corporation ( 世界图书出版公司 ) 《 Sears and Zemansky’s University Physics 》, H. D. Young etc, China Machine Press ( 机械工业出版社 ) 5

Chapter 1 Introduction, Measurement, Estimating 6

The Nature of Science Observation Theory Testing Aristotle and Galileo Galilei Three aspect of physics / science: Classical mechanics → Relativity & QM 7

Ideal Models Complex how many factors? Ideal models: Main factors & mathematical relationship Approximation & precision Is the model good enough? Falling objectApple & Water 8

Useful Models Mass point (particle) Translational motion Rigid body Rotational motion Other model for more complex motion 9

Measurement & Units Measurement, uncertainty Significant Figures: reliably known digits Units and Standards SI units ( length: meter, time: second, mass: kilogram ) Metric prefixes (Table 1-4, P7) e.g. nm, MB 10

Dimensions Type of units or base quantities that make it up dim A=[L p M q T r ] Dimensions of speed, force or angle? Dimensional analysis: 1.± or = can be only used between quantities with same dimensions. 2.Quantities in Exp, Sin or Log should be dimensionless (pure number). Check: a) mv=2mgl; b) cos(gt 2 -l)=1; c) C=v 2 /R+dv/dt 11

Order of Magnitude Rough estimate, power of 10 Example2: Estimate the volume of a lake. ( roughly circular, 1km cross, average depth of 10m ) Use flying papers to estimate the power of A-bomb Example3: Distance between the sun and the earth is about 1.5×10 11 m, and gravitational constant G= 6.67× N·m 2 /kg 2, try estimate the mass of the Sun. 12