For conservation of energy the loop the loop track is nice. You can calculate the height needed for the steel ball to just make it around the loop in terms of the loop radius. A meter stick is provided to measure loop diameter and height needed. Note: you actually need a tad higher than this due to friction and angular contributions.
A heavy steel ball will hang down in front of the chalk board from the ceiling by a string probably on Wednesday and Thursday. This is a pendulum which can be released from a position touching your nose. If you believe strongly enough in conservation of energy it will not hurt your nose on the return trip. Students may root for a hit after the midterm. Do not give any extra push.
The airtrack can be used as as last week with car launched by spring. But now discussed in terms of conservation of energy. The distance up the incline will be proportional to spring stretch.