Explain why, if you pour water into a glass very carefully, you can 'stack' the water slightly above the rim of the glass.

검증된 단계별 안내

Understand the concept of surface tension, which is the cohesive force between water molecules at the surface that allows the water to resist external force and maintain its shape.

Recognize that when you pour water carefully, the water molecules stick together due to hydrogen bonding, creating a sort of 'skin' on the surface that can hold the water above the rim without spilling immediately.

Consider the role of adhesion between the water molecules and the glass surface, which helps the water cling to the rim and supports the formation of a convex meniscus above the glass edge.

Note that the balance between gravitational force pulling the water down and the surface tension holding it together allows the water to 'stack' slightly above the rim before gravity overcomes the cohesive forces.

Realize that if you disturb the water or add too much, the surface tension breaks, and the water spills over, demonstrating the delicate balance maintained by these forces.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Surface Tension

Surface tension is the cohesive force between liquid molecules at the surface, causing the liquid to behave like a stretched elastic membrane. This allows water to resist external force and maintain a shape slightly above the rim without spilling immediately.

Cohesion and Adhesion

Cohesion refers to the attraction between water molecules, while adhesion is the attraction between water molecules and the glass surface. Together, these forces help water molecules stick to each other and the glass, enabling the water to form a convex meniscus above the rim.

Capillary Action and Meniscus Formation

Capillary action involves the movement of liquid within narrow spaces due to adhesion and cohesion. The meniscus is the curved surface of the liquid; in this case, the convex meniscus forms as water molecules cling to the glass edge, allowing the water to 'stack' slightly above the rim.