Pressure in fluids

• What is meant by the term ‘fluid’?

  A liquid or gas
• in any fluid, at what angle do the forces, due to pressure, act on a given surface?

  at right angles (normal to) the surface
• State the equation used to calculate pressure. Give appropriate units.

  Pressure = force/area

  • pressure (Pa), force (N), area (m squared)
• what happens to the density of the atmosphere with increasing altitude?

  the atmosphere becomes less dense as altitude increases
• explain why atmospheric pressure decreases with an increase in height

  • pressure is created by collisions of air molecules
  • the quantity of molecules (and so weight) decreases as the height increases
  • this means atmospheric pressure decreases with an increase of height
• what is the earth’s atmosphere?

  a thin (relative to the magnitude of the earth) layer of gas surrounding the earth
• how does pressure in fluids increase with depth?

  as the depth increases, the mass of liquid above that depth also increases. this means that the force due to the mass increases. since the force has increased whilst the area has remained constant, the pressure will increase.
• why does pressure in fluids increase with density?

  as the density of a fluid increases, the number of particles in a given volume increases. consequently the weight of the fluid is greater. this means that the force from the fluid above a certain point is larger. since the force has increased, the pressure also increases.