"Simple Physics is an iPad app that presents users with fun and challenging engineering problems. The app has twelve challenges that progress in difficulty as you move through the app. The premise of each challenge is the same. The challenge is to create a structure like a bridge or staircase that can support a given amount of weight. You’re given a budget for materials for each structure and you have to stay under that budget. When your structure is complete, test it to find out if it will work."
Via John Evans