Final answer:
A plastic ruler can attract paper bits after being rubbed due to static electricity, where the ruler becomes negatively charged and attracts the neutral or slightly positively charged paper.
Step-by-step explanation:
A plastic ruler can attract small bits of paper after being rubbed due to a phenomenon known as static electricity. When a ruler is rubbed with a cloth, electrons are transferred from the cloth to the ruler, making the ruler negatively charged. The bits of paper, being neutral or slightly positively charged, are attracted to the negatively charged ruler as opposite charges attract each other. This behaviour can be observed with various materials, such as plastic wrap clinging to surfaces or a comb attracting paper bits after running through hair, all due to the effects of electric force.