Unit 3 · 3.4 — Conservation of Energy

Everything to learn here

• Concept: In a closed, isolated system with no external work or nonconservative forces, the total mechanical energy is perfectly conserved and remains absolutely constant.
• Concept: Nonconservative forces do path-dependent work that dissipates mechanical energy into thermal energy, resulting in a change in the system's mechanical energy (W_nc = delta E).
• Concept: Defining the system boundary is the critical first step in an energy problem; if Earth is not in the system, there is no gravitational potential energy, only external work done by gravity.
• Equation: $$K_i+U_i+W_{nc}=K_f+U_f\text{(Conservation of Mechanical Energy equation with nonconservative work)}$$
• Equation: $$E_{t}otal=K+U\text{(Total Mechanical Energy)}$$
• Vocabulary: Mechanical Energy (Em) — The sum of all macroscopic kinetic and potential energies within a defined system.
• Vocabulary: Closed System — A system that does not exchange mass or energy with its surroundings.
• Skill: Creating Representations — Constructing Energy Bar Charts (LOL diagrams) to track the qualitative distribution of K, U, and W_nc before and after an event, ensuring total bar height is conserved for closed systems.
• Skill: Common Error Avoidance — Evaluating the presence of nonconservative work before equating initial and final mechanical states rather than assuming mechanical energy is always conserved.
• Vocabulary: Vocabulary: Mechanical Energy — The sum of a system's kinetic and potential energies, representing the total energy available for motion.
• Skill: Determine if a system's energy changes by identifying whether the forces acting on it are internal or external to the system.
• Concept: Any change in one form of energy within a system

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