Despite being 'easy' these are full-on scientific concepts. Nevertheless, they are explained about as clearly as possible by one of the finest scientists and communicators of the last hundred years. This isn't a casual read, but it is extremely interesting and mind-blowing. It got me so interested that I ended up buying the full set of Physics textbooks by Feynman!
I'd regard this as essential and enjoyable reading for anyone interested in the way the world works, as this explores some of the most crucial scientific theories that have a bearing on all aspects of science and nature. The structure and behaviour of atoms, quantum mechanics and gravity, are all covered superbly. By the end of the book, you'll still be fairly boggled by the concepts, but they are so fundamental to life, science and technology that there are few people who wouldn't benefit from at least some understanding of these landmark theories.