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Energy Musings

Energy Musings. Helen Quinn. Varied usage across fields. Physics : kinetic and potential energy, E=mc 2 Chemistry : bond energy, enthalpy… Biology : Food (or biomass) is energy Earth science : Energy flows (matter cycles) Engineering : energy resources, energy sources…

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Energy Musings

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  1. Energy Musings Helen Quinn

  2. Varied usage across fields Physics: kinetic and potential energy, E=mc2 Chemistry: bond energy, enthalpy… Biology: Food (or biomass) is energy Earth science: Energy flows (matter cycles) Engineering: energy resources, energy sources… Everyday: feeling energetic, mental energy…. Not just at school level but persists to Ph.D level

  3. Macroscopic view of energy • Motion • Mechanical • Electrical • Chemical • Thermal • Elastic • Gravitational • Radiation Overlaps and confusions, not defined or even definable

  4. Microscopic view of energy Motion of (massive) particles energy stored in gravitational, electromagnetic or nuclear force fields Radiation bridges the two • Travelling fields or quantum particles (photon, graviton) Every form of energy gravitates Mass = rest energy of any system, includes all energy types

  5. Key underlying ideas • System and system model (components, boundary) • States of system (configurations) • Processes within system • Processes across system boundary Without clarity on these any energy conversation is likely to be confused.

  6. Energy defines the physics Hamiltonian, H,expresses energy as a function of particle positions, motions and field strengths and changes. Conservation of energy follows from Noether’s theorem if H is frame invariant (does not depend on location or time or choice of coordinate frame of reference) Equations of motion (laws of physics for the system) derived from H

  7. The problem with mass-energy In all but nuclear physics, a large constant quantity compared to all energy transfers within and between systems under study. Best to remove it from the problem! The choice of what to set aside is arbitrary, leads to arbitrary zero of potential energy negative energies confuse students

  8. 4 messages for k-12 students • Only changes in energy matter (who cares how much you have if most of it is not negotiable). • Any change in energy is balanced by some other change in energy (you can’t make or destroy energy, only move it around) • Energy availability governs what can happen (you can’t do anything without energy) • Energy tends to spread itself around as much as possible (you cannot prevent losses from a system)

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