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Author Question: Why is an umbrella in danger of being turned inside out on a windy day? What will be an ideal ... (Read 130 times)

Mr.Thesaxman

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on: Jul 29, 2018
Why is an umbrella in danger of being turned inside out on a windy day?
 
  What will be an ideal response?

Question 2

Which is greater, the buoyant force that acts on an elephant, or on a helium-filled party balloon? Explain why the balloon rises in air and the elephant doesn't.
 
  What will be an ideal response?


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dreamfighter72

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Reply #1 on: Jul 29, 2018
Answer to Question 1

Answer: Because of the umbrella's curvature, air passes faster over its top than across its bottom. This produces a difference in forces, and like an airplane wing, experiences lift. This is in accord with Bernoulli's principle. The lift can turn or flip the umbrella inside out.

Answer to Question 2

Answer: The buoyant force exerted by the atmosphere on any body is equal to the weight of air displaced. Since an elephant has more volume, it displaces more air and has a greater buoyant force on it than the buoyant force on the smaller helium-filled balloon. Whether or not something rises has to do with the relative magnitudes of the buoyant force and the force due to gravity. Aha, the force of gravity on the elephant is enormously greater than the buoyant force on the elephant. So gravity wins and the elephant is pressed to the surface. But for the balloon, its weight is less than the small buoyant force it experiences. Buoyant force wins and the balloon rises.


Mr.Thesaxman

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Reply 2 on: Jul 29, 2018
Great answer, keep it coming :)

nguyenhoanhat

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Reply 3 on: Yesterday
Thanks for the timely response, appreciate it

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