CHAP1 General principle

1. CHAP1 General principle

2. CHAP1 General principle • Mechanics • Definition • A physical science studies the state of rest or motion of bodies subjected to the action of forces

3. Mechanics Rigid Body Deformable Body Fluids Statics Dynamics Incompressible Compressible Deformation/ stress Material Behavior CHAP1 General principle • Classfication

4. CHAP1 General principle • Fundamental Concepts • Basic Quantities • Length • The position of a point • The size of a physical system • Time • A succession of events • Mass • A property of matter • Force • A push or pull exerted by one body on another

5. Solution model Physical problem R r CHAP1 General principle • Idealizations or Models • Simplify application of the theory of mechanics • Particle質點 • A particle has a mass with a neglected size Ex: orbital motion of earth r<<R Earth a particle

6. F p1 p1 a b b’ a’ p3 p2 c p3 c’ p2 F CHAP1 General principle • Rigid body 剛體 • A rigid body is a combination of a large number of particles in which all particles remain at a fixed distance from one another both before and after applying a load before after

7. F Real physical problem Idealization model Loading area <<< the size of body CHAP1 General principle • Concentrated Force 集中力 • A force is assumed to act at a point in a body Concentrated force Distributed load

8. =0 F =0 M CHAP1 General principle • Newton's Three Laws of Motion • First law • Second law • Third law F=m . a F action=-F reaction

9. CHAP1 General principle • Unit of Measurement Quantity SI Units FPS Units Length m ft Time s s Mass kg Slug(lbs2/ft) Force N (kgm/s2) 1b

10. CHAP1 General principle • International System of Units Prefixes Exponential form prefix SI Symbol Multiple giga G mega M kilo K Submultiples milli m micro nano n

11. CHAP1 General principle • Numerical calculations • Dimensional Homogeneity • Each terms of any equation must be expressed in the same unit • 例: • Significant figures 有效數字 • A significant figure is any digit, including a zero, provided it is not used to specify the location of the decimal point for the number. (Ex. 5604 & 34.52 4 significant figures) • Numbers begin or end with zeros, then the number should be reported using power of 10. (Ex. 40, 4(10)1 or 0.4(102))

12. CHAP1 General principle • Rounding off Numbers 四捨五入 • The accuracy of the calculated result < the accuracy of the problem data • Rules for rounding off a number to n significant figure

13. CHAP1 General principle • Calculations: • In general we round off final answers to three significant figures since the data for geometry, loads, etc, are often reported with this accuracy.