The Velocity Incline

I wedged the end of a wooden ruler between two stacked hardcover volumes, creating an angled descent down to the floor. A clear glass marble sat ready at the upper rim. I released my grip. The sphere accelerated down the grooved surface and shot across the waxed planks, striking the skirting board with a sharp, clean click. Decent momentum. I stepped down from the plinth, retrieved the marble with two finger joints, and set it back at the summit to test a steeper incline.