The Physics of Star Trek was the first book on physics I had ever read, and it was the one of the things that really got me hooked on the subject. I cannot recommend enough. Do not worry if you cannot understand everything; I couldn't until I got a little deeper into the topics they present.
I would also suggest Physics of the Impossible by Michio Kaku for when you finish The Physics of Star Trek. It is a little harder, but it explores similar things like force fields and time travel. It is also a little more up to date. Kaku also divides the book into three parts: Class I Impossibilities, Class II Impossibilities, and Class III Impossibilities. They give a better idea of what may actually become a possibility. I would highly recommend both books. Enjoy reading.