Gas Pressure (HL IB Physics)

• Pressure is defined as

The force applied per unit area

• For example, when a drawing pin is pushed downwards:
  • It is pushed into the surface, rather than up towards the finger
  • This is because the sharp point is more concentrated (a small area) creating a larger pressure

When you push a drawing pin, it goes into the surface (rather than your finger)

• When an object is immersed in a liquid, the liquid will exert pressure, squeezing the object
  • The pressure exerted on objects in fluids creates forces against surfaces
  • These forces act at 90 degrees (at right angles) to the surface

The pressure of a fluid on an object creates a force normal (at right angles) to the surface

• The equation for pressure is:

• Where:
  • P = pressure (Pa)
  • F = force (N)
  • A = cross-sectional area (m²)
• Pressure is measured in Pascals (Pa)
• This equation is only relevant when gas molecules exert a force perpendicular to the surface

Gas molecules bouncing off the walls of a container

• It is possible for someone to experience this force by closing their mouth and forcing air into their cheeks
• The strain on the cheeks is due to the force of the gas particles pushing at right angles to the cheeks

• This equation means:
  • If a force is spread over a large area it will result in a small pressure
  • If it is spread over a small area it will result in a large pressure

High heels produce a higher pressure on the ground because of their smaller area, compared to flat shoes