Chapter 6 Force and Motion - II第 6 章 力與運動 ( 二 )

Chapter 6 Force and Motion - II

6-1 What is Physics?

6-2 Friction

6-3 Properties of Friction

6-4 The Drag Force and Terminal Speed

6-5 Uniform Circular Motion

6-1 What is Physics?

• frictional force 摩擦力• drag force 阻力• centripetal force 向心力

6-2 Friction

• static frictional force 靜摩擦力 fs• kinetic frictional force 動摩擦力 fk• cold-weld 冷熔接

The mechanism of sliding friction

6-3 Properties of Friction

,maxs s N

k k N

f F

f F

Sample Problem

Sample Problem

6-4 The Drag Force and Terminal Speed

• fluid 流體• drag force 阻力 D• drag coefficient 阻力係數 C• terminal speed 終端速率

21

2D C Av

• shot 鉛球• shot put 擲鉛球• sky diver 高空跳傘者• parachutist 跳傘者

6-5 Uniform Circular Motion

• A centripetal force accelerates a body by changing the direction of the body’s velocity without changing the body’s speed. 2

2

va

R

vF m

R

Sample Problem

Circular Motion

• loop-the-loop 騎單車翻圈子、倒飛觔斛• negative lift 負升力• Men in Black MIB 星際戰警• sedan 轎車• the verge of V-ing 瀕臨……• banked 傾斜 (tilted)

• bank 傾斜行駛

Sample problem

Sample Problem