In this brainteaser, students discover that sticky tape can pick up electrons as well as dirt, dust, and hair!
Electrons tend to move around, so there are usually free electrons moving around the surface of most objects, including tables. When you peel sticky tape off a surface like a table, it takes some electrons with it making it negatively charged.
In the first part of the activity, both tape A (with tape C taped on it) and tape B are peeled off the table, collecting electrons from the table. When brought together, they repel each other since they're both negatively charged.
In the second part of the activity, tape C is peeled off of tape A, collecting electrons from it. This leaves tape A positively charged, which attracts both the negatively charged tapes B and C.
Remember: opposite charges attract and like charges repel.