fluids

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fluids
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Fluids

• A fluid is a substance that has
• no definite form
• Is able to flow in all directions
• All liquids and gases are fluids
• The body is full of fluids- gas and liquid

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Fluids

• Powders such as sugar, flour or sand are not
  fluids even though they have no form and flow
• They are made of small particles of definite form
  

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Properties of fluids

• Fluid properties vary from one to another.
• Viscosity the ability of a liquid to flow
• Honey high viscosity
• Water low viscosity
• Density
• Humans use the properties of fluids for in
  various systems refrigeration, hydraulic
  systems, air bags, anaesthetic agent

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Pressure

• Pressure is the measure of the amount of force
  exerted on a certain area
• When we push on an object we apply a force on it
• If the force is high enough can move or even
  deform the object

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Pressure

• When we apply a force on a fluid, the fluid
  exerts a force on whatever contains it

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• Pressure (newtons/meter2) Force (newtons)
  
  Area (square meters)
• The international unit for pressure is the PASCAL
  (Pa)
• 1Pa 1N/m2 this is a relatively small unit
• kPa (1000Pa) is used to measure atmospheric
  pressure

Pssst This works the same as the Density Triangle
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• Other units are used to measure pressure
• Millimetres of mercury (mmHg)
• Atmosphere normal atmospheric pressure at sea
  level
• 101.3kPa760mmHg1atm

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The relationship between pressure and the area on
which the force is applied

• The force exerted on a floor by a person standing
  on it consists of the persons mass and the
  gravitational pull acting on it
• This is what we call a persons
• weight (mass x gravity)

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• By changing the area the force is acting on you
  notice an increase in pressure
• Increase area decrease pressure
• Decrease area increase pressure
  

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Pressure varies inversely proportional to the
surface area or force applied
5N/m2
0.5m2
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• If 1,000N were applied to an area of 100m2 what
  would the exerted force be?
• PF
• A
• If the same force (1000N) were applied to ½ the
  previous area( 50m2)
• PF
• A
• The pressure because the area was smaller
  

1000Newtons 100 m2
10N/m2
1000Newtons 50 m2
20N/m2
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• pressure is directly proportional to the force
  applied

Pressure (N/m3)
Force (N)
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• Look at these examples again
• If 1,000N were applied to an area of 100m2 what
  would the exerted force be?
• PF
• A
• If increasing the force (2000N) were applied to
  the same area( 100m2)
• PF
• A
• Double the force double the pressure

1000Newtons 100 m2
10N/m2
2000Newtons 100 m2
20N/m2
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Particle theory to explain pressure

• A tire pumped up with air has a force exerted
  upon it by the air inside.
• If the pressure is high enough the tire will
  remain firm even if pressure is applied to it
• This is explained by the air molecules inside the
  tire having lots of energy hitting the walls
• Adding more air increases the number of
  molecules pushing outward harder tire

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• In the body, fluids exert pressure on blood
  vessels (arterial pressure)
• The pressure difference causes fluids to move
  (from high pressure to low pressure)
• Lungs air moves into lung

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Compressible and incompressible fluids

• Compressibility is the capacity to reduce the
  volume by exerting a force
• A gas is a fluid that can be compressed because
  its particles are farther apart
• Air tanks for scuba divers, propane tanks

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• Liquids are
  incompressible
• Hydraulic brakes
• Incompressible- impossible to decrease the volume
  by exerting a force
• Instead of a change in volume there is a
  transmission of force from one particle to
  another inside the substance (like dominos)
• The blood forced through vessels by the pumping
  heart

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The relationship between volume and pressure of
compressible fluids

• Gases which are compressible fluids do not have a
  definite volume (it fits the container)
• If the container is flexible (balloon) then the
  volume can change

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• The volume and pressure are interrelated
• At a given temp. the larger the volume the lower
  the pressure (molecules farther apart)
• Decrease the volume the higher the pressure (more
  molecules hitting walls)