xkcd #2904: Physics vs. Magic ( imgs.xkcd.com )
Alt text:
‘At the stroke of midnight, your brother will be hurtling sideways at an altitude of 150 meters’ is a regular physics prediction about your nonmagical trebuchet, whereas ‘you are cursed to build a brother-launching trebuchet’ falls out of the Lagrangian.
![](https://kbin.pithyphrase.net/media/cache/resolve/entry_thumb/2a/b4/2ab407db7014149dc3330063a8a80c63b759b510c78c646f5ba04c2c41c8314a.png)