Friction (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

• Friction is a force that works in opposition to the motion of an object
  • Frictional forces slow down the motion of the object

• When friction occurs, energy is transferred by heating
  • Friction causes an increase in temperature of the object and its surroundings
  • The work done against the frictional forces causes this rise in the temperature

• Friction in solids is caused by imperfections in the surfaces of the objects moving over one another
• Therefore, friction:
  • decreases the speed of the moving object
  • increases the temperature of the objects due to heating 

Friction between surfaces

The interface between the ground and the sledge is bumpy, causing the frictional force

• Friction between solids can be reduced by:
  • lubricating the surfaces
  • smoothing the surfaces

• Gases and liquids are known as fluids
  • Fluids are different to solids because the particles in fluids are free to move around
• Friction acts on objects moving through gases and liquids as the particles collide with the object 
  • This type of friction is called drag

• Air resistance is a type of friction that slows the motion of an object moving through air
• Air particles bump into the object as it moves through the air
• Air resistance:
  • reduces the speed of the object
  • increases the temperature of the object and the air particles due to heating

The return module of a rocket heats up due to the work done by air resistance as it travels a distance through the atmosphere

• Friction in fluids can be reduced by:
  • streamlining the shape of the object moving through the fluid