Textbook Question
A 0.48-kg piece of wood floats in water but is found to sink in alcohol (SG = 0.79), in which it has an apparent mass of 0.047 kg. What is the SG of the wood?
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19. Fluid Mechanics
Buoyancy & Buoyant Force
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Why are some tiny insects able to walk on water?
A
Because they are repelled by water molecules.
B
Because they have special swimming abilities.
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 layer 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 tiny insects, to remain on the surface of a liquid without sinking, as long as their weight is not enough to break the surface layer.
Consider the balance of forces: For an insect to walk on water, the upward force due to surface tension must balance the downward gravitational force acting on the insect.
Analyze the interaction between the insect's legs and the water surface: The legs of the insect distribute its weight over a larger area, increasing the effectiveness of surface tension in supporting the insect.
Conclude that surface tension is the key factor: The ability of tiny insects to walk on water is primarily due to the surface tension of water, which provides the necessary support to prevent them from sinking.
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