Consider a test tube of water. The water surface is pulled near the tube's inner wall and forms a concave meniscus. However, in the case of mercury, a convex meniscus is formed. At the point of contact, if tangent lines are drawn to the solid surface towards the liquid and to the liquid surface away from the solid, the angle between the tangents is the contact angle. The contact angle is acute for liquids that rise along the solid surface and obtuse for liquids that are depressed. The contact angle measures how likely the liquid is to wet the solid surface. Liquid surfaces bend near a solid due to different forces at the point of contact. The adhesive force between the solid and liquid molecules is perpendicular to the solid surface, while the cohesive force between the liquid molecules is within the liquid. In addition, the weight acts downward. If the net force passes through the solid, a concave meniscus is formed. If it passes through the liquid, a convex meniscus is formed.