Atmospheric Pressure | Physics for Grade 10 PDF Download

The Atmosphere

• The Earth's atmosphere is a thin layer (relative to the size of the Earth) of air around it
  • It exerts a pressure of about 100 kPa at sea level
    
    The Earth's atmosphere
• The atmosphere extends more than 100 km into space and becomes less dense with increasing altitude (height above sea level)
  • This means that the pressure becomes less too
• Atmospheric pressure various slightly from day to day, depending on the weather, and fine clear weather is usually associated with high pressure

Atmospheric Pressure

• The graph below shows how the pressure varies with altitude:
  
  Graph of atmospheric pressure against altitude
• Atmospheric pressure varies with height above a surface, for example, at sea level
• This is due to air molecules colliding with a surface creating atmospheric pressure
  • These molecules create a force per area of the surface which creates the pressure
• The number of air molecules (and so the weight of air) above a surface decreases as the height of the surface above ground level increases
  • This is also known as the density of the air
• Therefore, as height increases, there is always less air above a surface than there is at a lower height and the atmospheric pressure decreases with an increase in height
  
  Atmospheric pressure decreases as the density of the molecules decreases

Exam Tip

Explaining why atmospheric pressure decreases with increasing altitude is a common exam question - make sure you can summarise these points!