Replying to Need ideas and thoughts!!

Alright so in my physical computing class we have to make something with arduinos (basically a mini computer). A project we discussed was a wearable sensor that will track motion and change the music on your iPod accordingly. For example, the harder you shred, the more hype the music will be that plays, etc. Another project could be technology that tracks anything such as speed, jumps, distance, etc.
If you have any ideas let me know!