Potential Energy and Conservation of Energy (Physics)

Recall cards on potential energy and the conservation of energy: potential energy as energy stored in a system because of the configuration of its interacting objects, the rule that the change in potential energy is the negative of the work done by the associated conservative force, the arbitrary additive constant and the choice of a zero reference, gravitational potential energy U = mgy near Earth's surface, and elastic potential energy U = (1/2)kx^2 for a spring. Conservative forces (path-independent work, zero work around a closed path) versus non-conservative dissipative forces such as friction and air resistance, recovering a conservative force from its potential energy by F = -dU/dx or the gradient, and the curl test. Mechanical energy E = K + U, its conservation when only conservative forces do work, W_nc = change in E when they do not, and the law of conservation of energy. Potential energy diagrams: the total-energy line, the condition K = E - U >= 0, turning points, allowed and forbidden regions, force as minus the slope, equilibrium points, stable versus unstable equilibria from the second derivative, maximum speed at a potential minimum, and the infinite potential well. And sources of energy: thermal, chemical, radiant, and nuclear energy, renewable versus nonrenewable sources, conversion losses, hydro, wind, and solar power, and the 2010 world energy shares.