Liquids

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Liquids

• Chapter 19

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Liquids

• While in the liquid phase, a substance will take
  the shape of their container, but will not expand
  to fill the container.
• In the liquid state, molecules can flow. They
  freely move from place to place by sliding over
  one another.

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Pressure in Liquids

• Any contained fluid exerts a force on the walls
  of its container. The ratio of this force to the
  surface area of the container is called pressure.
• F
• P A

• The unit for pressure is the Newton per meter
  squared, or the Pascal.

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Pressure in Liquids

• In a fluid, pressure is exerted equally in all
  directions.
• Therefore, the pressure always acts perpendicular
  to every surface.

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Pressure in Liquids

• For a liquid of uniform density, the pressure is
  proportional to the depth of measurement

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Pressure in Liquids

• For a liquid of uniform density, the pressure is
  proportional to the depth of measurement

Pressure weight density x depth Pressure
density x g x depth
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Pressure in Liquids

• For a liquid of uniform density, the pressure is
  proportional to the depth of measurement

Pressure density x g x depth
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Pressure in Liquids

• Pascals Vases demonstrate that the pressure of
  the liquid depends on the depth alone, and not
  the volume or shape of the fluid.

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Buoyancy

• When an object is placed in water, it weighs less
  than it did in air. This is due to an upward
  force exerted on the object by the water.
• The upward force is called the buoyant force.

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Buoyancy

• When an object is placed in water, it weighs less
  than it did in air. This is due to an upward
  force exerted on the object by the water.
• The upward force is called the buoyant force.

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Buoyancy

• If the buoyant force on an object is greater than
  the weight, the object will float.

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Archimedes Principle

• When an object is submerged in a liquid, some of
  that liquid is displaced.
• The volume of liquid displaced is equal to the
  volume of the immersed object.

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Archimedes Principle

• The Greek philosopher Archimedes determined the
  relationship between buoyancy and the amount of
  liquid displaced.
• An immersed object is buoyed up by a force equal
  to the weight of the fluid it displaces.

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Archimedes Principle
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Archimedes Principle

• The buoyant force depends on the volume of the
  object that is being submerged in the fluid
  nothing else matters.
• For every liter of volume (or 1000 cm3), there is
  a 10-newton buoyant force.

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Archimedes Principle

• For example, what is the buoyant force on
• - a half liter block of wood?
• - a 100 milliliter brass weight?
• - a 2 liter bottle of ginger ale?
• - a 2 liter bottle half full of ginger ale?
• - a 2 liter bottle full of air?

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Archimedes Principle

• The buoyant force acting on an object does not
  depend on the depth of the water.

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Density and Submersion

• Whether an object will sink or float in a liquid
  has to do with how great the buoyant force is
  compared to the objects weight.
• This can be summed up with three simple rules
• If an object is denser than the fluid in which it
  is immersed, it will sink.
• If an object is less dense than the fluid in
  which it is immersed, it will float.
• If an object has a density equal to the density
  of the fluid in which it is immersed, it will
  neither sink nor float.

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Flotation

• How can you make iron float?
• If the iron can be made less dense than water, it
  will float. This can be done by filling the
  piece of iron with pockets of air.
• This can be done by making bubbles in the iron as
  it cools, or by making a hollow object of iron.

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Flotation
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Flotation

• The Principle of Flotation
• A floating object displaces a weight of fluid
  equal to its own weight.
• For example, the aircraft carrier USS Enterprise
  weighs 90,000 tons.
• It displaces 90,000 tons of water.

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(No Transcript)
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Flotation

• To see how a submarine is able to make use of
  this principle to submerge and then re-surface,
  take a look at my website.

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Pascals Principle

• Changes in pressure at any point in an enclosed
  fluid at rest are transmitted undiminished to all
  points in the fluid and act in all directions.

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Homework

• Read ch 19 and do problems 1-20 on pages 280 and
  281.
• Due Monday, 3/6