Kurt Rosenkrantz is a science curriculum writer and Gizmo designer for ExploreLearning. Kurt holds a Master of Science in Geology from the University of Cincinnati, and a bachelor’s degree in Earth Science from Harvard. He taught high school and middle school science for eight years before joining ExploreLearning in 2005.
A while ago, a teacher named Joshua Buchman suggested a way to improve our popular Roller Coaster Physics Gizmo. In the Gizmo, a toy car rolls down a track, over several hills, and into an egg. The egg will either crack or not.
In the original Gizmo, the egg would crack if the momentum of the car was over a certain threshold value. Mr. Buchman pointed out that it was more likely that the kinetic energy of the car, rather than its momentum, would be the critical factor. He argued that the car would need to travel a certain distance into the egg, overcoming the resisting force of the eggshell, for the egg to crack. In other words, the car would have to do a certain amount of work to crack the egg, and the work it could do depended on its kinetic energy.
This argument made sense to us, but we wanted to check that it was true in practice before changing the Gizmo, which was designed with the help of real-world experiments that took place in the EL offices a decade ago. To investigate, I bought toy cars, a track, and several dozen eggs. I set up the track at a steep angle and went to work.
Right away I realized that I needed to establish a consistent definition of “egg breaking.” It turns out that a very tiny impact can cause a small fracture in the egg, and that the fracture grows bigger and bigger as the force of the impact increases. Eventually I decided that the most consistent criteria I could use was “eggshell breaks completely into two halves.” So, any fracture that did not go all the way around the egg was considered a negative result.
After several very messy sets of experiments using cars of different masses, I plugged the data into a spreadsheet. Sure enough, the minimum kinetic energy required to break the egg was much more consistent than the minimum momentum required to break the egg. With experimental results supporting the scientific argument, we decided to make the change. In the updated Gizmo, the car now needs to have a minimum kinetic energy of 0.25 J to break the egg. We have adjusted all of our lesson materials and assessment questions to reflect this new result.
We hope you enjoy the new-and-improved Roller Coaster Physics Gizmo, and thanks again to Mr. Buchman for bringing this to our attention!