1. 机械能守恒定律 Law of conservation of mechanical energy 珠海一中 杨林 ZhuHai No.1 Middle School YangLing

2. Vocabulary Mechanical energy 机械能 Kinetic energy 动能 Potential energy 势能 Gravitational potential energy 重力势能 Elastic potential energy 弹性势能 Gravity 重力 Free fall motion 自由落体运动 Pendular movement 摆动 Projectile motion 抛体运动

3. 1. 自由落体运动中能量的转化 Energy change the forms in the motion of free fall Energy change the forms in the motion of free fall 2. 竖直上抛运动中能量的转化 Energy change the forms in the motion of upright projectile Energy change the forms in the motion of upright projectile 3. 实验： experiment 小球在摆动中机械能守恒 小球在摆动中机械能守恒 The total mechanical energy remain constant in the pendular movement of the little ball The total mechanical energy remain constant in the pendular movement of the little ball

4. 4. 分析自由落体运动 : Research free fall motion again Research free fall motion again A h1h1 v1v1 B h2h2 v2v2 由动能定理得 : According to the theorem of kinetic energy 由功 _ 能原理得 : According to the work _ energy theorem We can substitute (1) to (2)

5. The above equation can be rewritten as or The above equation states that in the free fall motion.the sum of the kinetic energy and the potential energy(or total of mechanical energy) remain constant

6. Above result not only apply to free fall motion.but also apply to all kinds of motion that work is done upon an object by gravity or spring forces. Above result not only apply to free fall motion.but also apply to all kinds of motion that work is done upon an object by gravity or spring forces. Then we can get the law of conservation of mechanical energy. When work is done upon an object by gravity and spring forces.energe change forms _ from kinetic energy to potential energy (or vice versa).yet the total amount of mechanical energy is conserved.

7. Exercise Explain (KE to PE or PE to KE)? Answer (is the mechanical energy remain constant)? 1.A bungee chord begins to exert an upward force upon a falling bungee jumper. 2.The spring of a dart gun exerts a force on a dart as it is launched from an initial rest position. 3.A skier glides from location A to location B across the friction free ice.

8. 4.A baseball is traveling towards a man in the bleachers.ignore air friction force. 5.A weightlifter applies a force to lift a barbell above his head at constant speed.