Billboard has come up with a list of the 50 most popular songs about sex in time for Valentine's Day with each song given points according to its performance on the Billboard hot 100 chart from August 1958 until January this year. "Physical," released by Newton-John in 1981, topped the list after spending 10 weeks as No. 1 in the Billboard Hot 100 chart. And while it certainly speaks to sex with lyrics such as "There's nothin' left to talk about, unless it's horizontally," the song became known as well-known as a track for aerobics classes in line with the...