Hip hop was developed in New York in the 1970s primarily as a means to express political and social views. Hip hop was created mostly by African-Americans and people in poverty. Today, hip hop envelops a much wider culture and incorporates more technologically advanced beat machines and synthesizers.
Rock music originated in the 1940s and is an instrument-oriented genre. A typical rock band will have at least one guitar, a bass, drums and vocals. Some people credit the invention of rock music to Chuck Berry in 1955 when he recorded his first album, and he is known as the "Father of Rock and Roll."
There are many sub-genres of rock music, such as metal, punk, pop and funk. All or most of them have syncopation and time signature in common. Syncopation is the unexpected change of rhythm based on the primarily 4/4 time signature where an audience would clap along on beats 2 and 4. Syncopation creates an interesting rhythm that is unique by genre and artist and creates a variety of music.
Hip hop was originally created with man-made beats, turntables and rapped vocals then evolved into rapping, scratching, dancing and sampling with more technologically advanced equipment. Hip hop is also mostly in 4/4 time signature and uses syncopation in a different way from rock music. It generally has a syncopated beat with rapped lyrics layered on top, while rock usually has syncopated vocals. Rappers sometimes write, memorize or improvise lyrics to rap along with a back beat or a capella.
Both music genres have cultures behind the music. Hip hop's current culture includes dance and graffiti writing. Rock's culture has changed since its origins but has largely included drugs and sex appeal.