1. You can't write on the blackboard with chalk, because the powder at the tip of the powder can't be attached to the blackboard by static friction. Similarly, the written words can't be erased with the board.

2. Students who take notes can't write either, because the ball pen tip steel ball can't generate friction with the paper, so it will rotate and bring out the ink.

Students who want to answer questions can't stand up, because there is no friction between their feet and the ground, so they can't fix their bodies and make them upright and balanced.

Probably enough, 200 words, not much.