How can you increase the frictional force between two surfaces?

Question: How can you increase the frictional force between two surfaces?
- Keywords:
  force,
  friction,
  surface
Asked by smithmoorebell to Ben, Clare, Ezzy, Mario, Sam on 12 Mar 2012.
- Elizabeth Pearson answered on 12 Mar 2012:
  
  Friction is based upon two main things. How hard the two surfaces are being pushed together and the frictional coefficient ie. how rough the surfaces are. If you make the surfaces rougher or increase the weight pushing down then you increase the friction.

Question: How can you increase the frictional force between two surfaces?