Force and pressure

11.1 Pressure and surfaces

  • Pressure is caused when objects exert forces on each other, or when a fluid exerts a force on an object in contact w/ the fluid. Size of pressure depends on the area of contact on which the forces act and the size of the force
  • pressure (pascals, Pa) = force (N) / area (m^2)
  • Knives must be sharp so that there is a smaller area of contact and a larger pressure, so less force needs to be exerted

11.2 Pressure in a liquid at rest

  • The pressure of a liquid increases with depth.
  • The further the hole is below the level of water in the bottle, the greater the force w/ which the jet leaves the bottle because the water pressure increases as the holes get further down the bottle
  • Pressure in a liquid depends on the density of the liquid. Oil's less dense than water so water is below oil. 
  • pressure, p (Pa) = height, h (m) x density, p (m^3) x gravity, g (N/Kg)

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11.3 Atmospheric pressure

  • Atmospheric pressure is due to air molecules colliding w/ surfaces. Each impact exerts a tiny force on the surface, but the no. of molecules that…


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