Friction (Cambridge O Level 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

Friction Acting on a Sledge

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

Air Resistance Acting on Return Module

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