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