http://what-if.xkcd.com/8/ <- The What-If's are even better than normal XKCD :D
Yep I love XKCD and it's off shoots. There's so much rubbish written and broadcast on the Internet that we need sites like these to cut through all the rubbish. Plus I love questions that seem obvious but for which the answer isn't well known. Like why is the daytime sky blue? Why is the night time sky black? Why is it colder in Winter than summer? This last one got me completely. I thought it was about the earth being further away from the sun or something...... wrong.
Check out Vsauce and Minute Physics on You-Tube, they are excellent resources for finding out this kind of stuff.