Heidi, I am not sure of apps for Android for elementary level, perhaps I could look further. I teach science at college level, physics and math. And have used some Android apps to teach about motion and forces. One of them uses the accelerometer feature in most Android phones, that allow my students to have a sense of what is motion, and how forces are involved in the change of state of motion. There should be some apps on Android market and other sites which are free that may help you with some classes.