We've been looking at ways to help Quantopian members get more education about algorithmic trading. One of the places we've been looking for help is Khan Academy. Earlier today I watched the Khan Academy videos on short selling, and I realized that I could use Quantopian to help explain the Khan lessons.
First, you should check out the two lessons on Khan Academy:
http://www.khanacademy.org/finance-economics/core-finance/v/shorting-stock and http://www.khanacademy.org/finance-economics/core-finance/v/shorting-stock-2
Then you should watch my video:
http://youtu.be/g9pcX9NRjCw
When you're ready, just click the "clone algorithm" button below. That will give you a copy of the algorithm for you to play with, edit, and make further tests.