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Science 8 . Chapter 9: Fluids U nder Pressure. 9.1 Fluids Under Pressure A Problem with a Natural F luid S ystem. •Some infants are born with a condition known as hydrocephalus .

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science 8

Science 8

Chapter 9: Fluids Under Pressure

9 1 fluids under pressure a problem with a natural f luid s ystem
9.1 Fluids Under PressureA Problem with a Natural Fluid System

•Some infants are born with a condition known as hydrocephalus.

•A normal brain has fluid surrounding it, this fluid cushions the brain. In hydrocephalic babies there is too much fluid surrounding the brain and the excess fluid creates an increase of pressure inside the skull, causing a bulging skull, seizures, and even brain damage.

treatment for this condition
Treatment for this Condition

•Treatment = a tube is inserted in to the abdomen or another part of the body to drain the fluid.

•A check valve in the tube helps ensure that the pressure in the brain is correct and the fluid does not flow in the wrong direction.

fluids under pressure daily uses
Fluids Under PressureDaily Uses
  • Fluids under pressure are used daily: Compressed gases

Fire hoses

Vacuum Cleaners



  • Liquids many not be compressible, but by placing them under pressure in confined places such as pipes, we can force them to go where we want.
atmospheric pressure
Atmospheric Pressure
  • Earth’s atmosphere is 160km above us
  • The layers of air exert pressure due to gravity
  • Air pressure changes with altitude
  • If there is a difference in pressure between the inside and out side of your ear drum then you will feel a “pop” as the pressure equalizes
pressure differences
Pressure Differences
  • Fluids move from area of high pressure to are of low pressure
  • When this happens we use this force to drive many different types of mechanical devices ex. Juice box, air hammer, etc.
liquid pressure
Liquid Pressure
  • Pressure of all fluids increases with depth
  • Atmospheric Pressure at sea level is 101.3 kPa

= one atmosphere or 1Atm

  • Every 10m down = pressure increases by 1 atmosphere
  • = the tendency of objects to rise or sink due to the density differences between them and the surroundings
  • Upward force exerted by a fluid = buoyant force
  • Sinks—object exerts greater average force down
  • Floats-- object exerts greater average force upwards
rising and sinking
Rising and Sinking
  • Air heated will rise and expand; cooled it will condense and sink
  • Convectionis the vertical movement of fluids caused by density differences
  • Cause heat is evenly distributed through out the earth

Textbook Questions

Page# 323

Questions# 1-5 ( number 6 is a bonus)

Workbook pages 130-133

9 2 constructed fluid systems
9.2 Constructed Fluid Systems
  • Pressure in fluids at rest and in motion can produce a force to operate mechanical devices
  • Hydraulic systems – create pressure that moves through a liquid
  • Pneumatic systems – enclosed gases transmit force, causing motion
  • Ex. Water pumps used during Hurricane Katrina
fluids at rest
Fluids at Rest
  • Pascal – observed that when pressure is applied to one point ina fluid in an enclosed system, that pressure is transmitted equally throughout
  • (Ex. Squeezing toothpaste)
  • Squeezing an enclosed fluid creates static pressure (Ex. Car brakes)
fluids in motion
Fluids in Motion
  • A fluid in motion has dynamic pressure = energy to perform tasks
  • It can also be used indirectly to perform tasks
  • Speed of a fluid increases then pressure decreases
  • (Ex. Airplane wing)
hydraulic systems
Hydraulic Systems
  • Hydraulics = study of pressure in liquids
  • Hydraulic systems = devices that create pressure that moves a liquid
  • Liquids are not compressible so if a pressure is exerted it travels through the liquid to perform a task somewhere else
hydraulic fluid transportation
Hydraulic Fluid Transportation
  • Your water from your tap is always under pressure so that it will flow out when the tap is turned on
  • It can come from a well in rural areas or in urban areas it will go through a water treatment plant where it is pumped to reach all areas of the system
  • Pumps are important to hydraulic systems, so they can push water against gravity
  • A simple example is a piston pump
  • An important part of a hydraulic system that controls the passage of fluid through a pipe is the valve
  • Open = water flows Closed = water stops
  • Check valve allows fluid to flow in only one way
hydraulic multiplication
Hydraulic Multiplication
  • Mechanical systems can increase the force exerted on a fluid
  • We can use this force to even lift a car
problems in hydraulic systems
Problems in Hydraulic Systems
  • Pipe systems must be planned carefully so there is the least amount of resistance to flow
  • Pressure is affected by pipe size and how smooth they are inside
  • Water flow is affected by build-up in the pipes, corrosion, and mineral deposits
pneumatic systems
Pneumatic Systems
  • = the use of gas (usually air) in an enclosed system under pressure
  • Like hydraulics except they use gas instead of liquid
  • Pneumatic systems = gas transmits a force, causing motion
  • Based on the fact that gasses can be compressed
  • Using air compressors we can use many types of tools
  • Pneumatics can be combined with hydraulic multiplication an example would be air brakes on large vehicles
problems in pneumatic systems
Problems in Pneumatic Systems
  • There needs to be a difference in pressure between the inside of the machine and the air
  • If it gets clogged up then the system no longer works, because the air can no longer escape
  • Ex. A vacuum cleaner

Textbook Questions

Page 333

Questions# 1-4, 6

Workbook pages 136, 138, 139

9 3 natural fluid systems
9.3 Natural Fluid Systems
  • Natural fluid systems exist in the atmosphere, deep in the Earth, and in the oceans, as well as, inside humans
fluid systems in humans
Fluid Systems in Humans
  • Human body is about 66% water
  • Water helps you to absorb food, transport nutrients, remove wastes, protects tissues, and maintains blood pressure
circulatory system
Circulatory System
  • Efficient natural hydraulic system = circulatory system
  • Used to transport blood vessels are like pipes
  • Pump = heart
blood pressure
Blood Pressure
  • = the force of the blood on the walls of the blood vessels
  • Special nerve cells can detect this change and send messages to your brain to speed up or slow down your heart
  • Normal resting heart rates (60-100 beats per minute) adult and (80-100 beats per minute) children
  • Typical reading for blood pressure would be 120/75 mm Hg
  • First # = pressure from the blood leaving the heart
  • Second # = pressure from the blood refilling the heart
  • Blood pressure is measured using a


disorders of blood circulation
Disorders of Blood Circulation
  • Blood pressure is a good indicator to overall health
  • High/Low blood pressure
  • Ideal blood pressure is 120/80
  • Clogged arteries
  • Smoking causes problems
the respiratory system
The Respiratory System
  • Breathing is partly the result of changes in pressure
  • Chest expands to create an area of low pressure so air rushes in
  • This expansion is due to muscle groups between your ribs and your diaphragm
disorders of breathing
Disorders of Breathing
  • Clogged or swollen passageways affect natural systems
  • Bacteria, viruses, and other micro-organisms can cause infections (colds, bronchitis, etc.) and swelling occurs making it difficult to breathe
  • Breathing smoke, pollution, coal dust, or asbestos can harm your respiratory system
  • Asthma disease where air flow into lungs is altered
  • Using an inhaler can help
  • Textbook Questions

Page 343

Questions# 1-5

Workbook 143, 145