Energy is all around us. It is in the food we eat, the gasoline we put in our cars, and the sunlight that strikes our face. But what exactly is energy? It is a common everyday term, but its actual scientific definition differs somewhat from its everyday usage. Technically, energy is defined as "the ability to do work", where work is "the transfer of energy to an object by applying a force through a distance." What these two definitions mean when put together is that energy is the ability to change the motion of objects.

Pushing a box across the floor is a usage of energy, just as throwing a ball is. There are some uses of energy, though, in which it is hard to see the motion of objects changing. When we put a kettle of water over a flame, we are using energy to accelerate the motion of the molecules of water. When we turn on a television, we are increasing the flow of electrons through the system, and are thus using energy.

To power our modern way of life, we have to tap into large energy reserves. In these activities, we look at energy use and energy sources in depth.