Well one of the memory sticks would be unpartitioned and the other would contain a FAT32 partition with some music files on it.
Can the change in weight, if there is one, be proofed?
http://en.wikipedia.org/wiki/Flash_memory
Problem:
"What is the weight difference between an empty memory stick and the same memory stick when it contains data?"
Additional question:
Can the answer to the previous question be proofed?