Gr 3–4—Though presenting broad concepts well enough, these introductions to different kinds of energy are, at best, unsystematic when it comes to details. For instance, though the author explains in Heat just what BTUs measure, in Electricity she mentions amperes, volts, and watts without specifically defining their differences. Furthermore, readers may be more confused than enlightened by statements such as this one in Chemical: "A carrot is an example of chemical energy stored in plants." Captioned color and black-and-white photos illustrate the texts, and side boxes contain information on pioneering scientists such as James Joule and Nikola Tesla as well as additional facts. The glossaries and indexes are more scattershot than useful.