Final answer:
The free surface of gasoline poured into a cylindrical tank is flat. The shape is influenced by the liquid's tendency to minimize potential energy and is not affected by capillary action unless in a narrow tube where the interaction with the material matters.
Step-by-step explanation:
When gasoline is pouring into a cylindrical tank, the free surface of the gasoline assumes a flat shape. This occurs because gasoline, as a liquid, seeks to minimize its potential energy, resulting in a level surface when it is not interacting with other constraints such as a container's walls or forces such as capillary action. When considering capillary action in a narrow tube, the interaction between the liquid and the tube's material affects the shape of the meniscus. For example, with water in a glass capillary tube, due to the strong adhesive forces between water molecules and the glass's polar Si-OH groups, the surface level of water in the capillary will be higher than that of the surrounding water, forming a concave meniscus. Conversely, liquids like gasoline or motor oil that cannot form strong interactions with glass have a convex meniscus, akin to that of mercury in a glass container.