We did the gravity lesson with my 5-year old, and a couple of weeks after, while playing with a toy hydraulic lift, he mentioned “the energy of the hydraulic pressure makes the this lift go up, because the gravity is weaker than the pressure”. He came up with that on his own, based on the lessons we have given him so far, but I hadn’t been able to expand upon it until I saw this post. Thank you for the BFSU book, thanks to the lessons my boy often wakes up excited about science, wants to learn more, and says he wants to be a scientist when he grows up. This site is a treasure trove of information, will continue to refer to it for our lessons.