Science AHSGE Standard VIII

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Science AHSGE Standard VIII

• Objective 2- Pressure in Fluids

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Pressure

• Amount of force applied to an area
• Pressure Force / Area
• Metric unit of pressure- Pascal (Pa)
• One newton per square meter
• Common units include
• Atmospheres (Atm)
• Pounds per square inch (PSI)

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Atmospheric Pressure

• As you increase in elevation (distance above sea
  level), air pressure decreases
• Its harder to breath at the top of a mountain
  because the air is thinner
• As you down in elevation, air pressure increases
• Your ears pop as you go up or down in elevation
  or altitude (distance up in the air) in order to
  equalize pressure within your body with that
  outside

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Atmospheric Pressure
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Atmospheric Pressure
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Lungs and Air Pressure

• Air flows into and out of lungs when air pressure
  in the alveoli (lung sacs) differs from that of
  the surrounding air
• Higher alveoli pressure exhale
• Lower alveoli pressure inhale

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Water Pressure

• Downward pressure of water is equal to the weight
  of the column of water above an objects surface
  area
• The deeper you go, the greater the pressure
• When diving, ears also pop to equalize body
  pressure
• Water pressure in local water sources increases
  with the height of the water tower
• The higher the tower, the faster the water
  movement due to gravity higher water pressure

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Water Pressure
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Water Pressure

• High Pressure Gases in Liquids
• When liquid pressure is lessened, the gas is
  released as bubbles
• Ex Open a can of coke- Fizzes
• Ex The Bends- Painful condition caused by a
  build up of nitrogen gas in the body while
  surfacing too fast from a dive

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Turgor Pressure

• Fluid pressure inside a cell that keeps cell from
  collapsing in on itself
• Dehydration- Loss of turgor pressure
• Cell shrivels
• Wilting in plants
• Too much turgor pressure can cause cell to burst

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Blood Pressure

• The measurement of force applied to the walls of
  the arteries as the heart pumps blood through the
  body
• Determined by the force, the amount of blood
  pumped, and the size and flexibility of the
  arteries
• Systolic pressure- as heart beats Diastolic
  pressure- between heart beats
• Normal 120/80
• Which artery will have the lowest blood pressure?
  Highest?

A B C D
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High Blood Pressure

• Hypertension- Chronic high blood pressure
• Can be genetic
• Most characterized with blockages
• Stroke- Interruption of blood supply and oxygen
  to an organ
• Results in tissue damage
• Common to brain
• Caused by either bleeding or blood clots
• Fatty deposits and platelets collect on the walls
  of arteries

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High Blood Pressure

• Anuerysm- An abnormal widening or ballooning of a
  portion of an artery
• Can be congenial (present before birth)
• Can be caused by high blood pressure or blockages
  

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Pascals Priciple

• Pressure applied at any point inside a closed
  system with a confined fluid will transmit
  equally throughout the fluid
• Ex A balloon is a closed system applying
  pressure on one end will cause the same pressure
  throughout the balloon
• Ex Hydraulic systems are closed, confining
  either a gaseous or liquid fluid.
• Pressure applies to the smaller input piston
  first (F1 and A1) and transmits to the larger
  output plunger second (F2 and A2)
• Remember Pressure force/area
• Force is measure in newtons
• Area is measured in cm² or m²

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Try this!

• A force of 200 newtons is applied to the piston
  of 0.15 square meters, while a force is released
  from the 0.75 square meter plunger. What force is
  exerted from the plunger?

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