Chapter 8 Potential Energy and Conservation of Energy第八章 位能與能量守恆

Chapter 8 Potential Energy and Conservation of Energy

8-1 What is Physics?8-2 Work and Potential Energy8-3 Path Independence of Conservative Forces

8-4 Determining Potential Energy Values8-5 Conservation of Mechanical Energy8-6 Reading a Potential Energy Curve8-7 Work Done on a System by an External

Force8-8 Conservation of Energy

8-1 What is Physics?

• Potential Energy 位能 (U)– Gravitational Potential Energy 重力位能– Elastic Potential Energy 彈力位能、彈性位能– Electrical Potential Energy 電位能

• Technically, potential energy is energy that can be associated with the configuration of a system of objects that exert forces on one another

bungee 鬆緊繩bungee-cordbungee-cord jumperplunge 跳下

8-2 Work and Potential Energy

• Conservative Force 守恆力、保守力– Gravitational Force– Spring Force

• Nonconservative Force 非守恆力、非保守力– Kinetic frictional force– Drag force

• Thermal Energy 熱能– Thermal energy is not a potential energy

U W

8-3 Path Independence of Conservative Forces

• 與路徑無關的守恆力– The net work done by a conservative force

on a particle moving around any closed path is zero

– The work done by a conservative force on a particle moving between two points does not depend on the path taken by the particle

,1 ,2ab abW W

Sample Problem

8-4 Determining Potential Energy Values

• Reference point 參考點、基準點

( )

( )

f

i

f

i

x

x

x

x

W F x dx

U W

U F x dx

Sample Problem

8-5 Conservation of Mechanical Energy 力學能守恆

• Mechanical Energy 力學能– Kinetic energy 動能– Potential energy 位能

• Principle of Conservation of Mechanical Energy 力學能守恆原理

mec 0E K U

mecE K U

Sample Problem

8-6 Reading a Potential Energy Curve

turning point 轉折點equilibrium point 平衡點

轉折點與平衡點• turning point 轉折點• equilibrium point 平衡點

– unstable equilibrium– stable equilibrium

Sample Problem

8-7 Work Done on a System by an External Force

8-8 Conservation of Energy

• Law of Conservation of Energy

能量守恆定律、能量守恆律• Internal energy 內能• Isolated system 隔離系統、孤立系統

Sample Problem