1. 講者： 許永昌 老師 1

2. Contents A Short Catalog of Forces Identifying Forces Action I Newton’s 2 nd Law Action II Newton’s 1 st Law Free-Body Diagrams 2

3. Preface 3

4. ForceSymbolCause(Agent) Spring ForceSpring Tension ForceRope Normal Forcesurface Frictionsurface DragAir or liquid ThrustExhaust gas GravityThe earth Electric & magnetic Forces A Short Catalog of Forces The graphical description: Catalog: particle (1) (2) (3) Long range 4

5. Action I: Identifying forces ( 請預讀 P126~P134) 5

6. Exercise (gravity) 6

7. Identifying forces (pictorial representation) 7 Example: Anna pull a block. Example: Anna pull a block.

8. Summary I 力是造成運動的 “ 因 ” 。 Identifying forces method 可以幫助我們找出作用在該 感興趣的物體的所有的力。 這些力的合力滿足向量疊加法則。 8

9. Homework Student Workbook 5.1 5.2 5.3 5.5 5.7 9

10. Newton’s 2 nd Law ( 請預讀 P135~P139) An object with mass m will undergo acceleration 10 Q: However, the object is not a PARTICLE!! How can we apply the Newton’s 2 nd Law on an object? Q: However, the object is not a PARTICLE!! How can we apply the Newton’s 2 nd Law on an object?

11. Newton’s 2 nd Law of motion 11 *Shipman, An introduction to Physical Science, 12 edition.

12. General Physics experiment II Reference: http://www.5min.com/Video/Introduction-to- Newtons-Second-Law-174067905http://www.5min.com/Video/Introduction-to- Newtons-Second-Law-174067905 Observed: When an object is isolated, its motion is a uniform motion, i.e. v=constant. (both the magnitude & direction are invariant) Use the paper clips to pull the cart. You will find that the graph of acceleration vs. # of paper clips is almost a straight line. (Not only F pull   a , but also F pull  a) Compare the acceleration of one cart & of two carts. Theoretically, a  1/# of cart. Note: The condition m cart >> m paper clips should be held for these experiments. 12

13. Newton’s 1 st Law of motion & inertial reference frame ( 請預讀 P139~P142) 13

14. Summary II Newton’s 1 st Law of motion : 一物體若在孤立狀態下，則該物體會表現出 uniform motion 。 藉此定義出 inertial reference frame 。 Newton’s Law is valid in inertial reference frame. Newton’s 2 nd Law of motion: 此方程將 Dynamics and Kinematics 關連在一起。 14

15. Homework Student Workbook 5.9 5.11 5.13 5.15 5.17 5.18 5.20 5.21 5.22 5.23 15

16. Free-body diagram 16 x y The direction of the forces will be discussed later.

17. Summary 17

18. Exercise(5.28) Toss a rock straight up into the air. The rock is “ the system” of interest. Please draw a picture and a complete free-body diagram for each case. The rock is rest on your palm. Your hand is moving up but before the rock leaves your hand. One-tenth of a second after the rock leaves your hand. After the rock has reached its highest point and is now falling straight down. 18

19. Homework Student Workbook 5.24 5.26 5.28 5.29 Textbook: 5.4 5.21 5.30 5.53 一樣，將 terms and notation 製成卡片，以便自我練習。 19