Easy Demonstration of the Marangoni Effect by Prolonged and Directional Motion: "Soap Boat 2.0"

So-called "soap boats" have been known for decades and can be used to demonstrate the Marangoni effect. Inspired by recent scientific work, this paper reports an improved demonstration: a "soap boat 2.0". With this demonstration, a floating object (typically polystyrene foam) can be propelled along the water surface for up to several minutes. The direction of motion (straight, left-handed, or right-handed circles) can be influenced by the boat design. Three easy-to-make and effective boat designs are presented, and fifteen "fuels" have been considered with regard to safety, effectiveness, duration, ease of use, and availability. Some Other possible variations of the demonstration are also proposed. The demonstration can be done with any age group, lasts for up to several minutes, and can be turned into a student project of varying length. Readily available materials (e.g., polystyrene foam) and benign household chemicals (e.g., >= 10% 2-propanol ("rubbing alcohol") in water) can be used.