*October 9, 2024* # Free Energy ![[service-pnp-pga-07400-07482v.jpg]] > **Motive power (noun)**: An agency (such as water or steam) used to impart motion, especially to machinery I love steam engines because they are a potent metaphor for life. In addition, they quietly tell us the relationship between the four most fundamental quantities in the universe: *Energy, entropy, time, and space.* ## Entropy: misplaced energy There are some different kinds of energy. You might describe energy as the potential for change; something with energy can potentially do something, lead to something changing. In the physical world, energy is represented in many forms. As a rule of thumb, something *happens* when there is a transfer of energy. An apple falls from a tree, and gravitational energy flows into kinetic energy. A log burns, and chemical flows into heat and light. I'm still not sure I get what energy is, but at a ground level, you're not far off to think of it as *the currency in which things happen*. ![[rotated-doubled-Animated-mass-spring-ccw.gif]] A mass on a spring goes back and forth. Energy flows from compression, to velocity, to tension, and back again back and forth. ```mermaid graph LR B[Potential Energy] -->|acceleration| A[Kinetic Energy] A -->|compression/tension| B style A fill:#ff9999,stroke:#333,stroke-width:2px style B fill:#99ccff,stroke:#333,stroke-width:2px ``` In an ideal scenario, 100% of the energy flows in harmony with the oscillation. Energy passed from one form to another is fully re-payed each cycle, so the amount of energy in the system stays constant. In real life, when energy is transformed from one form to another, lots of other unintended stuff happens. Usually, there are several auxiliary channels that tax energy from the intended activity. ```mermaid graph LR subgraph Potential Loss C1[Elastic Deformation] C2[Heat] C3[...] end A[Potential] subgraph Cycle B --> A A --> B end B[Kinetic Energy] subgraph Kinetic Loss D1[Friction] D2[Air Resistance] D3[...] end C1 --- A C2 --- A C3 --- A B --- D1 B --- D2 B --- D3 style A fill:#99ccff,stroke:#333,stroke-width:2px style B fill:#ff9999,stroke:#333,stroke-width:2px style C1 fill:#d3d3d3,stroke:#333,stroke-width:2px style C2 fill:#d3d3d3,stroke:#333,stroke-width:2px style C3 fill:#d3d3d3,stroke:#333,stroke-width:2px style D1 fill:#d3d3d3,stroke:#333,stroke-width:2px style D2 fill:#d3d3d3,stroke:#333,stroke-width:2px style D3 fill:#d3d3d3,stroke:#333,stroke-width:2px ``` The usual theme is that over a period of time, some amount of the energy will go where you meant to put it, and the rest of it will flow into a million other little places you didn't. Energy is never created or destroyed, but it's easy to lose track of. **Energy that falls off the books is what we call *entropy*.** ## Time: spent energy To make a watch, we would make a mechanism to transfer kinetic energy out of the oscillator to some gears, which would advance hands on the face of the clock. Each tick, some energy would be spent to move the clock hand. ```mermaid graph LR subgraph inside clock A[Kinetic Energy] --> B[Potential Energy] B --> A D[Small Energy Waste] end A --> C[Advance Hand] style A fill:#ff9999,stroke:#333,stroke-width:2px style B fill:#99ccff,stroke:#333,stroke-width:2px style C fill:#90EE90,stroke:#333,stroke-width:2px ``` The spent energy can't be recovered. Some of it was lost to inefficiencies in the mechanical parts, some was lost prying the clock's hand into its next slot. A good watch must be very delicately crafted to be efficient; the cost of one second must represent a teeny-tiny fraction of the watches' energy, otherwise it won't last long enough to be useful. None of the energy spent on a tick is located somewhere specific; it's been distributed into the air and metal through sound and heat, like exhaust. We say the energy was *lost to entropy*. Of course, if we want a useful watch, we need a way to eventually restore energy that is spent. We can wind up the watch with its crown to tighten up the spring and add energy back to the cycle. ```mermaid graph LR E[Crown] --> B subgraph inside clock A[Kinetic Energy] --> B[Potential Energy] B --> A D[Misc Energy Loss] end A --> C[Advance Hand] style A fill:#ff9999,stroke:#333,stroke-width:2px style B fill:#99ccff,stroke:#333,stroke-width:2px style C fill:#90EE90,stroke:#333,stroke-width:2px style E fill:#90EE90,stroke:#333,stroke-width:2px ``` Some things to note: - Useable (free) energy in the system has a distinct location - The system has a distinct inside and outside, and specific ways to add to/extract the energy within - The system is aligned to spontaneously transform its free energy into useful work ## Engines: thermal clockwork At the end of the day, a steam engine is a really big watch. Instead of winding a crown, you add water and burn coal. Each tick advances the train's locomotion. ```mermaid graph LR A --> E[Crankshaft] D[Add Water] --> C G[Burn Coal] --> F[Raise Temperature] subgraph steam engine C[Boiling Water] --> B[Steam Pressure] B --> A[Piston] A --> B F end style A fill:#ff9999,stroke:#333,stroke-width:2px style B fill:#99ccff,stroke:#333,stroke-width:2px style C fill:#D8BFD8,stroke:#333,stroke-width:2px style D fill:#90EE90,stroke:#333,stroke-width:2px style E fill:#90EE90,stroke:#333,stroke-width:2px style G fill:#90EE90,stroke:#333,stroke-width:2px ``` In a steam engine, you burn coal, to boil water, to make steam. The steam expands, and pushes a piston out of its way to escape. The piston makes its round, drives a crankshaft, and comes down again. The crankshaft connects to some wheels, and your train moves. ![[Double_Acting_Oscillating_cylinder_steam_engine.gif]] You can imagine the piston bouncing on a cloud of hot, dense steam, much like a mass on a spring. When the steam escapes the chamber, the pressure goes down momentarily, but the boiling water provides a constant supply of steam to replace it, so the pressure stays high. The steam engine teaches something important: that disorder can be put to work. Heat and pressure are products of chaos, but together make a fine motive. When energy is cheap and work is useful, efficiency becomes less of a concern. The important difference between hot steam and "waste" heat is that hot steam wants to go somewhere. Definitively. While heat lost to friction is soaked up aimlessly, hot steam on the other hand has a clear "thermodynamic arrow" that we can point at the future to make specific things happen.