Why does a plastic strip become positively charged when rubbed with a cotton cloth?

Question:

Why did the plastic strip become positively charged when rubbed with a cotton cloth?

Answer:

The plastic strip becomes positively charged because it loses electrons to the cotton cloth during the rubbing process.

Explanation:

When Haley rubs a cotton cloth along a plastic strip and the plastic strip becomes positively charged, it's because the plastic strip has lost electrons to the cotton cloth. In the process called triboelectric charging, when two different materials come into contact and are then separated, one of the materials will end up donating some of its electrons to the other. Since electrons carry a negative charge, the loss of electrons means the plastic strip ends up with a deficit of negative charge and therefore becomes positively charged.