Sex and physics, two of my passions and now there is The Physics of Sex. What could be better, my two favorite subjects all rolled into one. This site has a three part series on why we have sex that is a great read link1, link2 link3 or if your are to lazy to move your eyes across the page you can listen to the podcasts 1, 2, 3. While you are there you might as well read about are Sexual Rhythms and Friction and Lubrication and how do we not love these subjects. These articles also available as podcasts.