Well, this week I found two references to physics at this point in HHGG. One is a mention of Improbability Physics, which applies to the improbability drive of the Heart of Gold. The other relates to Trillian, who in explaining her reason for hitching a lift with Zaphod says, "After all with a degree in Maths and another in astrophysics what else was there to do? It was either that or the dole-queue again on Monday...." [chapter 13]
My first inchie is the obvious one - probably the most famous equation in the world:
The quilled inchie was difficult. The definition of physics says in part that it deals with the structure of atoms. So I depicted an atom of water, with one oxygen molecule and two of hydrogen to get H20. I don't know -- it was a hard one this week. (Looks a bit like Mickey Mouse to me, now that I look at it.)