Well, I'll be jammed!: The Mystery and Intrigue of Amorphous Matter
"Many of us have experienced the frustration of trying to get stuck coffee beans out of a dispenser, throwing out expensive paint that has dried out and hardened, or even being caught in a traffic jam. These phenomena, along with the better known glass transition, are all examples of jamming---the transition of a many-body system from a fluid-like state to a disordered solid-like state with an extremely long relaxation time. The nature of the jamming transition is one of the oldest unsolved problems in condensed matter physics."
https://www.ithaca.edu/intercom/article.php/20071029111150324