2. System=block spring. The spring is within the system △K+△U Spring gra 3. System=block Earth Here gravity is an internal force △K+△U gra Spring 4. System=block spring Earth The spring force and gravity are both internal to the system, so △K+△U+△U 0 Spring grav Ch 13 Energy III: Conservation of energyCh.13 Energy III: Conservation of energy 2. System=block + spring. The spring is within the system. 3. System=block + Earth. Here gravity is an internal Force. 4. System=block + spring + Earth. The spring force and gravity are both internal to the system, so K + Uspring = Wgrav K + U grav = Wspring K + Uspring + Ugrav = 0