Forces in Fluids

1
Forces in Fluids

• Buoyant Forces

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Terms

• Buoyant Force the upward force that fluids
  exert on all matter
• Archimedes principle the buoyant force on an
  object in a fluid is an upward force equal to the
  weight of the volume of fluid that the object
  displaces

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Buoyant Force is Caused by Differences in Fluid
Pressure

• Determining buoyant force
• Based on the weight of the displaced liquid
• The weight of the object has nothing to do with
  buoyant force
• Ex

Block displaces - 250mL of water 250mL of water
2.5N Buoyant force 2.5N
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Weight vs. Buoyant Force

• Sinking
• An objects weight is greater than the weight of
  the water it displaces
• Ex. rock
• Floating
• An objects weight is equal to the weight of the
  water that it displaces
• Ex. Fish, duck
• Buoying Up
• When the buoyant force on the object greater than
  the objects weight
• Ex. Duck diving under and being pushed up

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Sketch picture on bottom of page 169
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An Object Will Float or Sink Based on Its Density

• More Dense Than Air
• Ducks dont float in air because they are more
  dense than air
• Most substances are more dense than air
• Less Dense Than Air
• Few substances are less dense than air
• Ex. Helium

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The Mystery of Floating Steel

• Steel 8 times more dense than water
• Ships can float because of shape
• Overall density less than water
• Built to displace more water to accommodate load

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A Ships Shape Makes the Difference
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The Mystery of Floating Steel

• Density on the Move
• Submarines have tanks to take on water to
  increase mass
• An increase in mass increases density
• Allows sub to sink (descend)
• How does it rise (ascend)?
• How is a Fish Like a Submarine?

10
VIDEO
11
Elements
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Non-animated still

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