Great question! My name is Humberto Valle, I'm the CEO and Competitive Strategist for Unthink Digital Marketing.

Your question has very simple answer:
Copy writing is the artistic use of words within advertising and or landing pages for example.
Figuring out a simple and clever way to make your point across is copywriting.
Catchphrases are copy, calls to action words are copy, Red Bull's "Vitalizes body and mind" at the bottom of their cans is copy.

Content Writing is just as complex or simple as copywriting but is actual writing of sentences and paragraphs or how tos, etc. Used primarily by inbound marketing agencies such as our www.Unthink.me; content writing is a way to help consumers find answers to their questions, provide them with solutions, etc as they move through their Buyer's Journey which goes from Awareness to Consideration to Decision - content writing should be written for each phase of the journey and each phase can have its own best type of content that is created for a certain persona at a specific phase in the journey.
-Consider me writing this answer for you if I had written this in a blog post and promoted it as an "Easy Comparison Between Copywriting and Content Writing" and my response was the article content - someone reading this would be within the Awareness phase.
- Copy was used in the title and possibly my call to action at the bottom of my blog offering you a "FREE eBook on blogging best practices" - this would take you a landing page that has more copywriting (clever wording to convince you give me your contact info exchange of the eBook) and the eBook itself is another way of content writing.

www.Unthink.me is known as the most helpful marketing agency in the world, for a low monthly subscription we help smart business owners with all inclusive inbound marketing and advertising campaigns.

Copywriting = writing with a call to action, meaning to sell. A sales letter, a squeeze page, a video sales letter (VSL) are all examples of copywriting.

Content writing = writing to inform or entertain. No call to action. Magazine-style articles, procedure manual content, and children's stories are examples of content writing.

Content marketing is, essentially, there to attract eyeballs, whether that is done by actually writing something people want to read or what a search engine thinks people want to read (which is not always the same... far from it).

Copywriting sells.

Copywriting is a copy that influence people to say yes to something.

Maybe it's to click to the link.

Maybe it's to book a call.

Maybe it's to download an ebook…

Whatever it is...

And content writing is to inform.

To add value, in advance.

Content marketing's purpose is to demonstrate how valuable you are, qualify the leads, and show people why they have to work with you, in advance.

Content writing basically builds trust.