Welcome to Science Buddies,
Here are some suggestions to get you started. Try the Science Buddies Project Wizard at: http://www.sciencebuddies.org/science-f ... deas.shtml
It will ask you some questions and recommend some science buddies projects to you. You can start there to see if any of them seem interesting. If not, the additional resources listed in any one of those might lead you to something else that catches your eye. In the mean time, A quick search and I came up with the following 3 that might be of interest...although they may be easier than you are looking for, but here goes:
Follow the Bouncing Ball: A Web Animation Project - http://www.sciencebuddies.org/science-f ... Q&from=TSW
You can always expand upon the basic premise of any project to make it more challenging. Please post back with any additional questions.
Hope this helps.
Science Buddies science fair guide:
Science Buddies project ideas: