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Mathematical expressions, which quantify how the stored energy in a system depends on its configuration (e.g. relative positions of charged particles, compression of a spring) and how kinetic energy depends on mass and speed, allow the concept of conservation of energy to be used to predict and describe system behaviour.

The potential energy between two objects due to long-distance forces can be thought of as being stored in a field. When the objects move due to the field forces, the energy stored in the field decreases

When two objects interacting through a field change relative position, the energy stored in the field is changed.

Energy is defined as the ability to do work. Energy can be found in many things and can take different forms. For example, kinetic energy is the energy of motion, and potential energy is energy due to an object's position or structure. Energy is never lost, but it can be converted from one form to another.

A discussion on how energy can't be created or destroyed in an isolated system, and works an example of how energy is transformed when a ball falls toward the Earth.

Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system’s total energy is conserved, even as, within the system, energy is continually transferred from one object to another and between its various possible forms.

Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. Magnets or electric currents cause magnetic fields; electric charges or changing magnetic fields cause electric fields.

The idea of the electric field, how it's useful, and explains how the electric field is defined.

Viewing g as the value of Earth's gravitational field near the surface rather than the acceleration due to gravity near Earth's surface for an object in freefall.

Basics of gravity and the Law of Universal Gravitation.