What If? (XKCD+)

For those who haven't already seen it, the outstanding XKCD comic now has a weekly "What If?" section,

"answering your hypothetical questions with Physics, every Tuesday"

or, as the main site puts it:

"abusing science to answer hypothetical questions".

I prefer this second description as the second question answered ("What if everyone who took the SAT guessed on every multiple-choice question? How many perfect scores would there be?") does not seem to have much to do with Physics. The inaugarul entry, however, "What would happen if you tried to hit a baseball pitched at 90% the speed of light?", has a definite Physics theme and is highly entertaining, complete with great XKCD illustrations. (The footnote at the end is also most excellent but I won't spoil the punchline here!)