Fluids Under Pressure

• Pressure is the amount of force applied to a given area. Air is fluid, and it applies pressure around you all the time.
• Pressure (p) = force (F) / unit area (A)
• Closer to the surface of the Earth,  we experience more air pressure, there is less air pressure if we travel to higher altitudes.
• Pressure in a fluid changes with depth. For example, the weight of water in the upper part of a swimming pool presses down on the water in the lower part of the pool. 
• If a fluid is allowed to move, it will go from an area of higher pressure to an area of lower pressure. 
• The most compressible state of matter is gas. 

  That is because there is a large amount of space between the particles in a gas like the air in a ball. When you kick a soccer ball, it is easy to force the air particles inside into a smaller volume.
• There is much less space between the particles in a liquid than a gas. 

  When a force is applied to the 

  particles, much more compression 

  takes place in the gas than in the liquid. This means gases are morecompressible than liquids.
• Liquids are difficult to compress because they have some space between their particles, but always occupy the same volume and space. 

  If you try to compress a liquid with a lot of pressure, then the liquid will flow wherever the space is. 
• Solids can’t really be compressed. 

  The particles in a solid are so closely packed together that there is no room for them to move.
• Compressibility is the ability of matter to be compressed.