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Buoyancy

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A regularly shaped object is immersed in water of density 1000 kg/m3. ... What weight of water will be displaced by 25 kg of floating pine? ... – PowerPoint PPT presentation

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Title: Buoyancy


1
Buoyancy
2
Why is there buoyant force?
  • A regularly shaped object is immersed in water of
    density 1000 kg/m3.
  • Calculate the liquid pressure on the top of the
    object.
  • Calculate the liquid pressure on the bottom of
    the object.
  • Find the difference in the pressures.

3
When will it float?
  • When the weight of a submerged object is
  • greater than the buoyant force,
  • the object will sink
  • less than the buoyant force,
  • the object will float
  • equal to the buoyant force,
  • the object will remain at any level

4
Finding Buoyant Force
  • Archimedes Principle
  • An object completely or partially immersed in a
    fluid is pushed up by a force that is equal to
    the weight of the displaced fluid.
  • Fb pfg?V
  • Archimedes Principle is consistent with Newtons
    3rd Law
  • If something pushes water (or any fluid) with a
    force of 100 N, then the water pushes back with a
    force of 100 N.

5
Example
  • Palmer drops an ice cube into his glass of water.
    The ice (density 917 kg/m3) has dimensions
    0.03m x 0.02 m x 0.02 m. What is the buoyant
    force acting on the ice cube?
  • Before you startwill the ice cube float or sink?

6
Another Example
  • Williams wedding ring, presumed to be pure gold,
    has a mass of 0.1 kg. When submerged in water,
    its apparent mass is 0.080 kg. The density of
    water is 1 kg/L.
  • What is the buoyant force (in Newtons)?
  • What volume of water (in liters) is displaced?
  • Is the ring made of pure gold? The density of
    pure gold is 19.3 kg/L.

7
And another
  • Pine is ½ as dense as water and therefore floats
    in water.
  • What weight of water will be displaced by 25 kg
    of floating pine?
  • Think firstthe pine is FLOATING
  • What additional force would be required to
    completely submerge the pine?
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