Plastic and glass rods that have been charged by rubbing with wool and silk, respectively, hang by threads.

a. An object repels the plastic rod. Can you predict what it will do to the glass rod? If so, what? If not, why not? Explain.
b. A different object attracts the plastic rod. Can you predict what it will do to the glass rod? If not, why not? Explain.

a. When you rub a plastic rod with wool, it becomes negatively charged. This is because the wool material loses some of its electrons to the plastic rod. The wool becomes positively charged while the plastic rod becomes negatively charged.

Hence, for an object to repel the negatively charged plastic rod, it must also be negatively charged. This is because objects with like charges repel one another.

On the other hand, when you rub a glass rod with a silk material, it becomes positively charged. This is because the glass rod loses its electrons to the silk material. The silk material then becomes negatively charged, while the glass rod becomes positively charged.

Therefore, the negatively charged object will attract the already positively charged glass rod.

b. For an object to attract a negatively charged plastic rod, then it must be positively charged, since unlike charges attract.

So, a positively charged object will repel the negatively charged glass rod.