Students use real world scenario to understand forces. My students love this lab, it's hilariously fun, educational, and students really grasp the idea and have a concrete visual to cement the force concept.
If you have any specific questions please ask, for I adjusted as I went with this lab. ASU science extravaganza had something like this on display and I just adapted to make it work for my students.
Engaging the students in science can be a battle, this lab is not a battle! They absolutely love it! My administration and district staff were amazed by the level of fun and excitement that comes from using "poo" to hook the kids into lab.