Fluid and Fluid Dynamics

• Fluid Mechanics is the study of the effects of forces and energy on liquids and gases.

  It subdivides into Fluid Statics (often called Hydrostatics) and Fluid Dynamics.
• Fluid Statics deals with the characteristics of fluids at rest or when there is no relative

  motion between the fluid particles. Some concepts under this branch include density,

  pressure, buoyancy, and surface tension.
• Fluid Dynamics studies fluids in motion. It has several subdisciplines,

  including Aerodynamics (the study of air and other gases in motion) and

  Hydrodynamics (the study of liquids in motion). Its development has been strongly

  influenced by numerous applications on the fields aeronautical engineering,

  meteorology, and even the study of blood flow, the dynamics of swimming, and the

  flight of creatures.
• Gases are highly compressible. Putting gas under a lot of pressure allows

  you to put a much greater mass of gas into smaller container.
• liquids are barely compressible. Under great pressure or force, a

  liquid will maintain a volume very close to its original volume.
• Gas and liquid has both indefinite shape
• Gases

  will expand to fill the entire space,
• liquids will maintain a relatively

  constant volume so they will not necessarily fill a container’s volume.
• Viscosity is

  the fluid’s resistance to flow.
• Gases have very very little viscosity,
• liquids run the

  scale on viscosity – from the more viscous end of the scale to the less viscous
• In gases, the molecules are randomly spaced relatively far apart. They

  basically bounce around all over the place because they are not held by

  strong forces of attraction.
• Liquids, when compared to gases, contain

  molecules that are quite packed together.
• Density is a measure of the compactness of matter – of how much mass occupies a

  given space.
• Water, for example, has a mass

  density of 1000 kg/m3
• Hence, to create a large

  amount of pressure, you can either exert a large force or exert a force over a small

  area (or do both).
• Simply put, the pressure of liquid exerts against the sides and bottom of a container

  depends on the density and the depth of the liquid.
• Pressure is depth dependent, not volume dependent,
• Pascal's Principle : A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid.
• There is a force pushing up on the ship that

  opposes the gravitational force, pulling the ship

  down. What is this force that pushes up on the

  ship? This upward force is called the buoyant

  force,
• Archimedes' principle : An immersed object is buoyed up by a force

  equal to the weight of the fluid it displaces.
• An object more dense than the fluid in which it is immersed will sink.
• An object less dense than fluid in which it is immersed will float.
• An object having a density equal to the density of the fluid in

  which it is immersed will neither sink nor float.
• Surface tension is caused by molecular attraction.
• capillarity, the

  rise or depression of a liquid in a fine, hollow tube or in a narrow space.
• the attraction between unlike substances is called adhesion;
• while the

  attraction between like substances, “molecular stickiness”, is called cohesion.
• Smaller diameter

  tubes have more relative surface area inside

  the tube, allowing capillary action to pull water

  up higher than in the larger diameter tubes.
• Daniel Bernoulli (1700-1782) was a Swiss scientist who

  studied the properties of moving fluids, such as water

  and air.
• Bernoulli’s principle,

  Where the speed of a fluid increases,

  internal pressure in the fluid decreases.