"The Case of the Missing Joules" For ages 9-14. A two-page story about how energy can change forms (for instance, from calories to horsepower) written in a humorous style. There are also six follow-up (easy, one-step) math problems that use an energy conversion table (wouldn't you know it--the very same one the Detective Agency uses in the story!).
This is a high-quality, kid-friendly FREE video series you might find very helpful. These videos were made around 1980, but have a nostalgic 1970's feel to them. They are whimsical but very high content, suitable for use with elementary up through high school. Just combine these videos with an experiment book and you've got a great curriculum! You can access them via my youtube channel: "YouTube.com/eejm63" or you might want to try this channel, where they are loaded with a menu to the right, giving the title and contents of each film: http://www.animatedscience.co.uk/flv/