Two decades ago theorists began to investigate how objects move through viscous fluids when pulled close to a soft, springy surface. They predicted that objects would experience a counterintuitive lift force, even at low speeds. One of those theorists, L. Mahadevan of Harvard University, recently joined Baudouin Saintyves, Theo Jules, and Thomas Salez in devising and running an experiment to test that and other predictions. Depicted here, their setup consists of a glass tank filled with silicone oil. Inside the tank is the test surface: an inclined pane of glass coated with a layer of soft polymer that is embedded with fluorescent particles. When the test object, an aluminum cylinder, rolls or slides down the layer, the combination of a sheet of laser light and a video camera monitors the cylinder’s motion and the layer’s response. As the cylinder moves, it’s expected to push down on the soft layer...

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