Change in most things is inevitable, and that is true about the English language--or nearly any language, really. It should not surprise that, just as fashion and music changes, so does language. Some things about our language change quickly and others change over time.
All languages change over time, and vary from place to place. They may change as a result of social or political pressures, such as invasion, colonisation and immigration. New vocabulary is required for the latest inventions, such as transport, domestic appliances and industrial equipment, or for sporting, entertainment and leisure pursuits. But a language can also change by less obvious means.
One of the primary reasons language changes or evolves is because the world changes and evolves. One great illustration of this is technology. For example, that thing we keep our perishable foods in was once called an icebox. The name was apt because, well, people came and delivered ice into boxes so people could keep some things cold (or at least cool). Soon we had refrigerators, then freezers. These changes happened over the past century. Another example is the radio, which was once called a wireless, and this change happened over the past seventy years or so.
During the past several decades, however, language has changed much more quickly to adapt to the innovations in technology. While the names of different types of products have obviously changed, it is our use of the technology which have caused the most recent additions to our language.
Not so very long ago, "sexting" was unheard of, "googling" someone was not possible, "flash mobs" did not exist, I will be "spell-checking" this answer, and "tweeting" was something only birds did. These are all based relatively new words which are based on our use of technology.
Another way language changes is through popular use. In the past decade, some phrases have become quite familiar in the realm of economics and business. We nearly fell off a "fiscal cliff" and we have certainly reached our "debt ceiling." A word that we once used to describe what some juries have to do, "sequestration," has now become an economic policy.
Finally, language changes through social interaction. As people interact with other people who do not have the same vocabulary, changes, amalgamations, meldings, and re-workings happen. One that readily comes to mind is the word "thong." When I was growing up, this was a thin beach-type shoe, generally made out of soft rubber; today, however, a thong is certainly not something people wear on their feet--and we have a new word, "flip-flops." Think about your own family intergenerational vocabulary for more examples of this one.
It is clear that language changes to meet the needs of its innovations but also due to popular culture and social interaction.