Textbook Question
Estimate the diameter of a steel needle that can just barely remain on top of water due to surface tension. (See Figs. 13–38 and 13–39a, and Table 13–1.)
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19. Fluid Mechanics
Buoyancy & Buoyant Force
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Why can some insects walk on water?
A
Because they have special swimming abilities.
B
Because they are repelled by water molecules.
C
Because of the surface tension of water.
D
Because they are less dense than water.
Verified step by step guidance1
Understand the concept of surface tension: Surface tension is a physical property of liquids that makes the surface behave like a stretched elastic membrane. It is caused by the cohesive forces between liquid molecules.
Recognize the role of surface tension in supporting small objects: Surface tension allows small objects, like insects, to remain on the surface of a liquid without sinking, as long as their weight is not enough to break the surface.
Consider the size and weight of the insect: Insects that can walk on water are typically small and light enough that their weight is supported by the surface tension of the water.
Examine the structure of the insect's legs: Many water-walking insects have legs that are covered with tiny hairs or are shaped in a way that maximizes the surface area in contact with the water, enhancing the effect of surface tension.
Conclude that surface tension is the key factor: The ability of some insects to walk on water is primarily due to the surface tension of water, which prevents them from sinking, rather than their density or any repulsion by water molecules.
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