Fluids

• Fluid


  The common name for gas and liquid
• Fluids


  • Can have the capacity to flow
• Fluid pressure


  Caused by collisions of the fast-moving atoms or molecules of a fluid
• Pressure


  A scalar quantity, force per unit area, measured in Pascals
• 1 atm is approximately 10 N/cm2 of surface area
• 1 atm = 101.3 kPa
• Blood pressure


  The blood pressure in the arteries is as much as 20 kPa higher than atmospheric pressure
• Density


  The mass per unit volume of a substance
• Measuring pressure with a manometer

  1. Manometer indicates the pressure relative to the atmospheric pressure

  2. Mercury manometer consists of a vertical U-shaped tube, containing some mercury, with one side typically open to the atmosphere and the other connected to a vessel containing a gas whose pressure we want to measure

  3. When both sides of the manometer are open to the atmosphere, the mercury levels are the same

  4. If we connect an inflated balloon to the left side of the U-tube, the gas in the balloon is at a higher pressure than the atmosphere, the gas pushes the mercury down on the left side and forces it up on the right side
• Barometer


  Instrument for measuring atmospheric pressure
• Sphygmomanometer


  Instrument for measuring blood pressure
• Steady flow


  The velocity of the fluid at any point is constant in time
• Laminar flow


  The fluid flows in neat layers so that each small portion of fluid that passes a particular point follows the same path as every other portion of fluid that passes the same point
• Unsteady flow


  The flow velocity at any point changes erratically
• Turbulence


  An example of unsteady flow
• Ideal fluid


  Incompressible, undergoes laminar flow, and has no viscosity
• Continuity equation


  1. Expression of conservation of mass for an incompressible fluid

  2. The total mass of the fluid must be constant
• Bernoulli's equation


  A form of the energy conservation law applied to fluid flow
• Bernoulli's principle


  1. The speed is higher where the pressure is lower

  2. Arterial flutter and aneurisms

  3. Airplane wings
• Viscosity


  The resistance of a fluid (liquid or gas) to a change in shape, or movement of neighbouring portions relative to one another
• Surface tension


  The tendency of fluid surfaces to shrink into the minimum surface area possible