The walls of your classroom are in motion but appear stationary. Explain

It all depends on the choice of the reference frame, means from where the observer is watching the classroom.

From anywhere within the earth the walls of the classroom will be stationary with respect to the Earth because the person sitting in the room is moving with the room as well with the same velocity of the Earth (the velocity due to rotation and revolution of earth), since the room is located on the earth. 

But, from outside the earth, from space, the observer will perceive the walls of the  classroom to be moving, because the observer in the space wouldn't be in motion with the earth.  

For example - A person sitting inside a moving car will be in motion from the reference of an observer standing outside of the car, while the same person will be at rest with the reference of the observer sitting with him/her inside the car.