Why do gases exert a pressure on the walls of their container?

Question: Why do gases exert a pressure on the walls of their container?
- Keywords:
  exert,
  gas,
  gases,
  pressure,
  walls
Asked by mikeala98 to Alex, Jools, Lynz, Matt, Rika on 22 Jun 2011.
- Matthew Dickinson answered on 22 Jun 2011:
  
  This is a great question, for example lets take fuel, As fuel is ignited the reaction is to draw all the air away from the chamber, this effect causes the energy from the fuel to grow (expansion) this effect puts a large level of pressure on the container. This is the best way I can explain this hope it has helped

Question: Why do gases exert a pressure on the walls of their container?