This 21 minute screencast recording & narration covers making a "Reversed Gravity" game in the Scratch programming environment.
Scratch is a free programming educational tool from MIT for kids and teens. It can be used in the browser or downloaded to your Windows, Mac, or Linux PC. https://scratch.mit.edu/
In this game, the player must jump to avoid crabs. Not only does the viewer learn how to implement gravity physics, but they also make a "reverse gravity" mode and have the character walk on the ceiling. The viewer can follow along as the narrator puts the program together one code block at a time from scratch.
You can play this game yourself at https://scratch.mit.edu/projects/11776786/#editor
This video and others can be found at the http://inventwithscratch.com website.
These videos are released under a Creative Commons license and are free to copy and share.