Couple I knew were giving a brand new, cab-over-engine, engine between the seats, van by Daddy (a Ford dealer). They moved to an area with lots of snow, and he, Big Brain that he was, decided that they needed more weight in the back for traction.

He found and put in a 1,000 pound safe.

One nice day, weather clear, road dry, no snow, he slammed on the brakes.

Every hear of inertia? He learned about it when the safe slid forward and hit the engine compartment.