Radio waves are what cell phone company rely on
Rubbing both pieces cause each piece to have a negative charge.
When two parts have the same they repel each other, so holding one piece up tot he end of the other piece would push it away.
Because one piece is held in the middle by a string, it would rotate the piece in a circle.
If they held the piece to the other end of the one held by a string it would start to rotate in the opposite direction.
2 minutes is 120 seconds, so if you were finding vibrations per minute, it would be 60 times a minute.
