pressure

• pressure is...


  the force per unit area
• pressure


  the amount of force exerted per unit area of a surface
• fluids are substances that can flow because...

  their particles are able to move around - as they move around they collide with surfaces and other particles
• particles are light but...

  they still have a mass and exert a force on the object they collide with
• the pressure of a fluid means a force is...

  exerted normal (at right angles) to any surface in contact with the fluid
• pressure (Pa) =


  force (N) / area (m²)
• pressure formula


  P=F/A
• pressure formula triangle

  
• pressure in a liquid depends on...

  depth and density
• density


  the measure of the compactness of a substance - how close together the particles in a substance are
• for a given liquid the density is...

  uniform (the same everywhere) and doesn't vary with shape or size
• the density of gas can...

  vary over a wide range because the molecules are free to move
• the more dense a given liquid is...

  the more particles it has in a certain space
• more particles in a certain space means...

  there are more particles that are able to collide so the pressure is higher
• as the depth of the liquid increases...

  the number of particles above that point increases. the weight of these particles adds to the pressure felt at that point
• liquid pressure increases with...

  depth - this is because of the weight of the fluid above it
• pressure (Pa) =


  Height (m) x density (kg/m³) x gravitational field strength (N/kg)
• pressure formula


  p=hpg
• gravitational field strength on Earth

  9.8 N/kg (or 10 N/kg)
• objects in fluids experience...

  upthrust
• when an object is submerged in a fluid (either partially or completely)...

  the pressure of the fluid exerts a force on it from every direction
• pressure increases with...


  depth, so the force exerted on the bottom of the object is larger than the force acting on the top of the object
• a larger force exerted on the bottom of a submerged object causes a...

  resultant force, known as upthrust
• upthrust


  a force that pushes things up in liquids and gases.
• the upthrust is equal to the...

  the weight of fluid that has been displaced by the object
• an objects floats if its weight equals...

  upthrust
• if the upthrust on an object is equal to the objects weight...

  then the forces balance and the object floats
• if an objects weight is more than the upthrust...


  the object sinks
• whether an object floats or not depends on...

  its density
• an object that is less dense than the fluid its place in weighs ... than the equivalent volume of fluid


  less
• an object being less dense than the fluid its placed in means...

  it will displace a volume of the fluid that is equal to its weight before it is completely submerged, making the object's weight is equal to the upthrust, so it floats
• an object less dense than the fluid its in will...

  float
• an object that is denser than the fluid is unable to ... enough fluid equal to its weight

  displace
• an object unable to displace enough fluid equal to its weight means...

  its weight is always larger that the upthrust, so it sinks
• an object more dense than the fluid its in will...


  sink
• how do submarines make use of upthrust?

  - to sink, large tanks are filled with water to increase the weight of the submarine so that it is more than the upthrust- to float, the tanks are filled with compressed air to reduce the weight so that it is less than the upthrust
• the atmosphere is a layer of...

  air surrounding the earth
• atmospheric pressure


  the pressure exerted by the weight of the atmosphere
• atmospheric pressure is created on a surface by...

  air molecules colliding with the surface
• as the altitude (height above the Earth) increases...

  the atmospheric pressure decreases