Friction (CIE IGCSE Physics)

• Friction is a force that works in opposition to the motion of an object
  • This slows down the motion of the object

• When friction is present, energy is transferred in the form of heat
  • This raises the temperature (thermal energy) 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 
  • Not only does this slow the object down but also causes an increase in thermal energy

The interface between the ground and the sledge is bumpy which is the source of the frictional force

Friction in Fluids

• Gases and liquids are known as fluids
  • Fluids are different to solids because the particles in fluids can 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
• Particles bump into the object as it moves through the air
  • As a result, the object heats up due to the work done against the frictional forces

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