Inertia

Newton's First Law of Motion says that objects at rest tend to stay at rest until a force pushes or pulls the objects.

To demonstrate this, I put a piece of paper on an upside-down cup, then put another, right-side-up cup on top of the paper. When I just pulled on the piece of paper, the top cup fell. However, when I held the piece of paper out and hit it with a really quick downward motion of my free hand, the paper came out without the top cup falling over!

This happened because the paper moved fast enough to overcome the friction between the cup and paper, but too fast to overcome the inertia of the top cup, so the top cup stayed at rest. This trick also worked with a piece of satin and a smooth TV tray. I was able to drop coins into a jar and keep books on the table. Using a cloth dish towel and a fabric bench top didn't change much, but the books moved a little more because of the increased friction.