Every now and then we come across homemade roller coasters designed by amateurs and built in their own backyards. While we appreciate the effort and creativity that goes into building one, most look poorly made and are of questionable safety. That is until we discovered Paul Gregg, a retired aerospace engineer who holds 29 US and foreign patents, two special invention awards, and was Boeing Aerospace Engineer of the Year in 1988. Paul uses his engineering skills to design and test his backyard roller coasters until he can prove they are reasonably safe to ride and operate, which I'm sure his grandchildren love! We recently got to ask Paul a few questions about how he uses math, science, and his engineering experience to design and build backyard roller coasters and why he decided to write a book about it.