I decided to look for apps for the iPad that let you drag and build circuits - I came across "Exploriments" which is a set of app science experiments on different topics, all very hands-on. The first one is free and explores weight and mass letting you try playing with weight differences on different planets,
Check out their Blog HERE
Here is a demo video on their unit on electrical circuits
Here is a link to their app page that explains insights in the different units and shows demo videos for some of them.
The Unit I downloaded had an overall actions button that showed what the activity chosen can do and how to manipulate it. It was very easy to use. The insight button gave you a set of scrolling index card style insights 1-10 of things learned in each activity. The free mass/weight app had 3 built-in activities each on a concept.
For students that need hands-on ways to learn material, I would highly recommend checking these out. They range from free to 3.99 for individual app topics such as units on motion, weight and mass, electricity, optics, Newton's Law, compunds, Pendulums, Vectors, etc.
Teachers may be interested to know they have these available for use on a computer for the Promethean and SMART board.
Have fun Exploring!