Intro
This week shifts mechanics into an energy lens. Instead of tracking every force through every moment, you start asking how energy moves, where it is stored, and how representations like bar charts make those transfers visible.
Core Lesson
Work is energy transfer by a force acting through a displacement. Kinetic energy tracks motion. Potential energy tracks useful configuration or position within a chosen system. The power of energy thinking is that it often simplifies situations that look messy in force language.
Energy representations matter because they keep the bookkeeping visible. A bar chart can show whether energy is entering, leaving, being stored, or being dissipated. The system boundary controls what counts as internal, external, conserved, or transferred.
The right question is often not “what formula matches this noun?” The better question is “what is my system, what forms of energy matter here, and how are they changing?”
AP Lift
The AP exam rewards representation switching in energy problems. Students may need to move from a physical scenario to an energy bar chart, then to a conservation statement, then to a written justification. The representation work is part of the physics.
Must-Master Objectives
- Describe work as energy transfer.
- Distinguish kinetic energy from stored energy in a chosen system.
- Use energy bar charts or transfer language to describe a scenario.
- Explain how the choice of system changes the energy story.
Problem Set Prompts
- A box is pushed across a rough floor. Name one way energy enters the box-floor system and one way useful mechanical energy leaves it.
- Why can an energy bar chart be helpful before writing equations?
- A ball falls toward Earth. What energy forms are changing if the system is ball plus Earth?
- A spring is compressed and released. What two energy forms are most obviously trading?
- A student says “energy disappears because friction is present.” Improve the statement.
- How can changing the system boundary simplify an energy problem?
- A cyclist pedals up a hill at constant speed. Why is this still an energy-transfer problem?
- Stretch: Describe a situation where force language is possible but energy language is cleaner.
- Stretch: Explain why work can be positive, negative, or zero.
Reflection Prompt
- When you see a mechanics situation, do you naturally think in forces or in transfers and storage?
- What part of energy language still feels least stable: system choice, work, storage, or dissipation?