Notes

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Notes Pressure Buoyant Force

• Chapter 3, Lesson 2

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Pressure in a Fluid

• A fluid is a material that can flow and has no
  definite shape.
• Liquids and gases are fluids.
• Fluids can exert forces.

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Pressure in a Fluid

• Pressure is the force per unit of area applied on
  the surface of an object.
• Pressure depends on the area over which a force
  is exerted.
• If the area increases, pressure decreases.

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Pressure in a Fluid

• Pressure depends on the size of the force.
• If the force increases, pressure increases.

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Pressure in a Fluid

• The equation for pressure is P F A
• Pressure (pascals) force (newtons)
• area (meters
  squared)
• The SI unit of pressure is the pascal,
  abbreviated Pa. A pressure of 1 Pa is equal to a
  force of 1 N applied over an area of 1 m2
• 1 Pa 1 N / m2

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Pressure in a Fluid

• For any liquid in a container of any shape, the
  pressure depends only on the height of the column
  of liquid above the surface where you measure the
  pressure.

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Pressure in a Fluid

• The deeper underwater you go, the greater the
  pressure is on you. This is because as you go
  deeper, the column of water above you gets
  taller.

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Pressure in a Fluid

• In a fluid, pressure is exerted on all points on
  the outside of an object in a direction
  perpendicular to the surface of the object at
  that point.

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Pressure in a Fluid

• A gas, like any fluid, exerts a pressure on an
  object. That pressure depends on the height of
  the gas above the object.

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Pressure in a Fluid

• Atmospheric pressure is the force exerted per
  unit area by air particles.
• As you climb, or increase your elevation,
  atmospheric pressure decreases.

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Pressure in a Fluid

• Atmospheric pressure at sea level is caused by a
  large weight of gas, but is difficult to notice
  because there is an equal, internal pressure
  pushing out from the inside of your body.

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Buoyant Force

• The buoyant force is the net upward force exerted
  on an object in a fluid by the surrounding fluid.
  It acts against gravity.

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Buoyant Force

• In a fluid, there is no net horizontal force on
  an object caused by pressure from the fluid.

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Buoyant Force

• Because in a fluid, pressure increases with
  depth, the force of the fluid pushing up on the
  bottom of an object is always greater than the
  force of the fluid pushing down on the top of the
  same object.

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Buoyant Force

• The size of the buoyant force does not depend on
  depth.

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Buoyant Force

• Archimedes Principle states that the buoyant
  force on an object is equal to the weight of the
  fluid the object displaces.

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3.2 Pressure and the Buoyant Forces
Pressure is the ____ per unit area. A mass B volum
e C force D pascal
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3.2 Pressure and the Buoyant Forces
Which direction does the buoyancy force act on an
object? A upward B downward C to the left of the
object D to the right of the object
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3.2 Pressure and the Buoyant Forces
Where is the pressure the greatest on an object
in a fluid? A top B bottom C sides D none of the
above
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Vocab Pressure Buoyant Force

• TB p. 140-148
• force
• fluid
• pressure
• atmospheric pressure
• buoyant force
• Archimedes principle