Who doesn't love learning about science from Bill Nye The Science Guy? His videos were a huge part of my classroom instruction when I taught 3rd, 4th, and 5th grade for years. Bill Nye's videos were entertaining and factual and students love them. He now has an iPad app that can access some of these videos as well as activities to reinforce science concepts. Students can "sit" at Bill Nye’s desk and choose what they want to learn about. There is some in app purchase material, but much can be done with no cost.
Below are some screen shots of the app in use. It is a great app to have students learn about science.