Fluid Mechanics

1
Fluid Mechanics

• Chapter 8

2
Mass Density

• The concentration of matter of an object,
  measured as the mass per unit volume of a
  substance.
• Represented by the Greek letter ? (rho)
• mass density ( ? ) mass/volume
• Units kg/m3

3
Buoyant Force

• Upward force exerted by a liquid on an object
  immersed in or floating on the liquid.
• Because the buoyant force acts in an opposite
  direction as the force of gravity, the net force
  acting on an object submerged in a fluid, is
  smaller than the objects weight.
• Objects appear to weigh less in water than they
  do in air so the weight of an object in a fluid
  is the objects apparent weight.

4
Your Turn!

• Why does an air mattress float and a brick sink?
  Think of an answer and make sure you put it in
  terms of forces.

5
Eureka!!!

• Archimedes Principle- Any object completely or
  partially submerged in a fluid experiences an
  upward buoyant force equal in magnitude to the
  weight of the fluid displaced by the object.
• Does this mean that the buoyant force is just
  like weight (mg)?

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Buoyant Force

• FBFg(displaced fluid)
• FBmfg
• In other words
• The magnitude of the buoyant force equals the
  weight of fluid displaced
• What does Fg equal?
• Based on Archimedes Principle, what would be a
  good equation for FB?

7

• Fg -FB apparent weight
• Fg-apparent weight FB
• Fgmg
• FB ? V g
• Where did ? V come from?
• What is V?

8
Sink or float?
Buoyancy Largest Ascend Forces Balanced
Hover Weight Largest Sink
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