American Association of Physics Teachers
Com Padre Digital Library: Open Source Physics: Scalar Field Gradient Model
Students investigate scalar and vector fields though a downloadable java simulation. The simulation explores the gradient of a scalar field using a numerical approximation to the partial derivatives.
PBS
Pbs Learning Media: How Big Is the Universe?
In this media-rich essay from the NOVA Web site, astronomer Brent Tully of the University of Hawaii walks you through the latest scientific theories about the size of the universe.
Wikimedia
Wikipedia: Electrical Potential
Wikipedia provides detailed information on electrical potential, including a definition, introduction, and mathematical formulas.