I recall them saying you don't have to do anything. Just stop participating and they will know whether you are active or something like that

Good to know because I leaped before I looked, never had AP level physics and barely any calculus but 1/3 of the way through an electronics cert.

I had the same question; looks like the parent post is correct. I found the FAQ here:

http://mitx.mit.edu/6002x-faq.html

"How do I drop the course?

You do not have to do anything. You can simply stop working on the course at any time you choose to do so.

What happens if I drop the course?

For the prototype course, learners achieving grades of "A," "B," or "C" will receive an electronic Certificate of completion with the learner's name and grade on it. If you receive a grade below a "C" or do not complete the course, you will not receive a Certificate and no grade record attaching your name to your participation in the class will be disclosed outside of MITx. You can also choose to opt for a no record at any time. However, the posts you make while enrolled in the class will remain visible."

Thanks for the info :)