Fluid Mechanics: Why Golf Balls Have Dimples
How liquids and gases push, flow, lift and drag, from floating steel ships and draining sinks to water hammer and wings.
Fluid Mechanics · 50 questions
Try 3 questions
1. Heating honey makes it runnier. What happens to the viscosity of air when it is heated?
- It decreases
- It increases
- It stays the same
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Answer: It increases
Gas viscosity comes from molecules carrying momentum between layers; hotter molecules move faster, so air gets more viscous.
2. A steel needle laid gently on water can float, even though steel is much denser. What holds it up?
- Surface tension of the water
- Air trapped inside the steel
- Buoyancy from its displaced water
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Answer: Surface tension of the water
The water surface acts like a stretched skin; the needle dents it, and surface tension supports its small weight.
3. Why do lakes freeze from the top down instead of from the bottom up?
- Ice forms only where wind blows
- Water is densest at about 4 °C
- The bottom is warmed by the sun
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Answer: Water is densest at about 4 °C
Water colder than 4 °C is lighter and stays on top, so ice forms at the surface and insulates the water below.
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