Destin Sandlin, host of Smarter Every Day (based in Huntsville, Alabama) and Derek Muller of Veritasium (who's in Sydney) each filmed a video from their respective hemispheres to MythBust this oft-quoted scientific tidbit. The two vids are meant to be watched in sync, and are filmed in such a way that the dialogue, music, and effects mesh up as though it's one video.
It's a collaboration the YouTube stars have been planning for three years, and we've embedded the vids here on one page for your convenience. Press play on one video, pause at the sync mark, start the other one, and re-start the first one when they both match up:
In the guys' experiment, they each filled a kiddie pool with water. They didn't want to just go off tubs and toilets — there are too many variables there. Toilets have jets in them that influence water flow, and no matter where you are on Earth, there will be toilets and sinks that drain clockwise, and others that flow counterclockwise.
Each kiddie pool was filled and allowed to sit for 24 hours. Then the guys pulled plugs from underneath each tub, dropped in some food colouring for visual aid, and waited with bated breath.
The results? Water did indeed drain counterclockwise in Alabama, and clockwise in Australia. As the Earth spins on its axis, it pulls water in different directions depending on where you are. We can see this in nature with the Coriolis Effect: hurricanes in the northern hemisphere spin counterclockwise, while the south's cyclones whip clockwise.
Sync up the videos and prepare yourself for some great science YouTubing. It's well worth the trouble.