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講者: 許永昌 老師 1. Contents 2 後面幾章的重點 Action: Law of Conservation of mass ( 請預讀 P239) Purpose: Realize the meaning of “conservation”. Realize the significance.

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Presentation on theme: "講者: 許永昌 老師 1. Contents 2 後面幾章的重點 Action: Law of Conservation of mass ( 請預讀 P239) Purpose: Realize the meaning of “conservation”. Realize the significance."— Presentation transcript:

1 講者: 許永昌 老師 1

2 Contents 2 後面幾章的重點

3 Action: Law of Conservation of mass ( 請預讀 P239) Purpose: Realize the meaning of “conservation”. Realize the significance of “before” and “after”. Action: Water + Juice  Drink Before: m water and m juice. After: m drink. Conservation: m water + m juice = m drink. 3

4 Momentum and Impulse ( 請預讀 P240~P247) 4 JxJx t(s) F x (N)

5 Action: Impulse 5

6 Example 9.1 A 150 g baseball is thrown with a speed of 20 m/s. It is hit straight back toward the pitcher at a speed of 40 m/s. The interaction force between the ball and the bat is shown in the graph. What maximum force F max does the bat exert on the ball? 6 t(s) F x (N) 6.0 ms F max

7 Student Workbook P9-3 A carnival game requires you to knock over a wood post by throwing a ball at it. You’re offered a very bouncy rubber ball and a very sticky clay ball of equal mass. Assume that you can throw them with equal speed and equal accuracy. You only get one throw. Which ball will you choose? Why? 7

8 Homework Student Workbook:

9 Summary I 9

10 Law of Conservation of Momentum ( 請預讀 P247~P252) System: Total Momentum: Net force: Newton’s 2 nd Law of Motion: For a System: 10 這就是為何我們常常 簡化問題為 particle 的 樣子。

11 Collisions ( 請預讀 P253~P255) 11

12 Explosions ( 請預讀 P255~P257) System: Fuel+Rocket Before: P i,y =(M+  m)v i,y. Final: P f,y =Mv f,y +  m(v f,y +v thrust,y ). We get: 12

13 Examples: Textbook: 9.45: An object at rest on a flat, horizontal surface explodes into two fragments, one seven times as massive as the other. The heavier fragment slides 8.2 m before stopping. How far does the lighter fragment slide? Assume that both fragments have the same coefficient of kinetic friction. A 10 g bullet is fired into a 1.0 kg wood block, where it lodges. Subsequently, he block slides 4.0 m across a floor (  k =0.20 for wood on wood). What was the bullet’s speed? 13

14 Homework Student Workbook: Student Textbook: 一樣,請製作卡片。 14


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