Physics I

Wu Hao

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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

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Water of pool

Example1: It need 4 hours to fill a pool, 3 hours to empty, how about both switch is turned on?

1 12 ?1 3 1 4

Is water flow constant?

dm comes out in dt h

ghdm2

2v dm 2 ,v gh

dh kvdt

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About the course grade

30% for the midterm,

40% for the final exam,

30% for the attendance, homework, quiz,

project and so on.

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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 )

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Chapter 1Introduction,

Measurement, Estimating

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The Nature of Science

Observation

Theory

Testing

Aristotle and Galileo Galilei

Three aspect of physics / science:

Classical mechanics → Relativity & QM

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Ideal Models

Complex how many factors?

Ideal models:

Main factors & mathematical relationship

Approximation & precision

Is the model good enough?

Falling object Apple & Water

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Useful Models

Mass point (particle)

Translational motion

Rigid body

Rotational motion

Other model for more complex motion

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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

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Dimensions

Type of units or base quantities that make it up

dim A=[LpMqTr]

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(gt2-l)=1; c) C=v2/R+dv/dt

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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 1.5×1011m, and gravitational constant G= 6.67×10-

11N·m2/kg2, try estimate the mass of the Sun.

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