This lab has students try to stop a simulated asteroid from hitting the Earth. It's a lab that grabs student attention quickly and provides them with a lot of fun while they learn about conservation of momentum. It takes one full 50-minute class period and requires a computer lab. Equivalently, it could be assigned for homework, but it's a lot easier to assess when the teacher can watch the students work.
This lab is suitable for introductory physical science or for a low-level physics course.