講者： 許永昌 老師 1

Contents Goal of this chapter Action: K and W Action: Work is  Fcos  dr=  F  dr. Work-Kinetic Energy Theorem Conservative and Nonconservative forces Conservation of Energy Power 2

Goal of this chapter 3

Energy Transfer and Energy transformation ( 請預讀 P303~P304) 4 E th KU SYSTEM Energy transfer

Action: K and W ( 請預讀 P302~P306) 5 F F

Action: Work done by a force F is  Fcos  dr ( 請預讀 P307~P309) 6 

The dot product of two vectors ( 請預讀 P310~P311) Geometric: Algebra: E.g. A=(1, 1) B=(sqrt(3), 1) A  B=? 請同時使用兩種算法算看看。 7 A B A B A B

Exercise of work-kinetic energy theorem A 2.0 kg ball is lifted upward on a string. It goes from rest to a speed of 2.0 m/s in a distance of 1.0 m. What is the tension (assumed to stay constant) in the string? Method 1: by Newton’s 2 nd Law of Motion Method 2: by Work-Kinetic Energy Theorem. 8

Homework Student Workbook 11.1, 11.2, 11.3, 11.9,

Summary I 10

Conservative and Nonconservative force ( 請預讀 P312~P316) 11 A B A B

Conservative and Nonconservative force (Continue) 12

Exercise A 1.0 kg block whose velocity is v x =2.0 m/s at x=0 m moves along the x-axis. Assume that there is only one kind of force exerted on this block and F x -versus-x graph is shown as follows. Calculate the velocity of this block at x=5 m or it never gets to x=5 m. Plot the potential-versus-x graph. 13 x (m) F x (N)

Finding force from potential energy ( 請預讀 P317) Since we get Therefore, 14 梯度

Homework Student Workbook 11.14, 11.15, 11.17, 11.19,

Summary II 16

Center of Mass ( 請預讀 P343) Based on Newton’s 2 nd and 3 rd Law of Motion: If we define We get 17 X

Kinetic Energy 18 X X X 考慮旋轉時，會把 K rot 由 K micro 中抽離出， 也當作 Kmech 中的一個。

Potential energy contributed from the internal forces 19

System and Environment ( 請預讀 P318~P322) Work-kinetic energy theorem: W net =  K. K=K macro +K micro. W net =W c +W nc W c =  U mech  U micro W nc =W ext ( 這裡與課本不同的是， dissipative force 在微觀尺度其實也是來自 保守力，所以已經被計算在 U micro 裡頭了 ) We get: 20

System and environment ( 請預讀 P323~P324) Work-kinetic energy theorem 21 Conservation of Energy System W Q Wave, …

Power ( 請預讀 P325~P327) 22

Exercise A 0.5 kg cart and a 2.0 kg cart are attached and are rolling forward with a speed of 2.0 m/s. Suddenly a spring-loaded plunger pops out and blows the two carts apart from each other. The smaller cart shoots backward at 2.0 m/s. What are the speed and direction of the larger cart? If the spring constant of the plunger is 25,000 N/m, by how much was the spring initially compressed? 23

Summary III 24

Homework Student Workbook 11.22, 11.23, 11.25, Textbook 請自行練習 Terms and Notation ( 製造字卡 ) 25