Pouring oil into an engine. Image credit tenerifenews.com

Pouring oil into an engine. Image credit tenerifenews.com

ZIMSEC O Level Combined Science Notes: Dealing with friction in machines

  • Friction is the force that opposes all movement
  • It is the resistance that one surface or object encounters when moving over another
  • Work must be done to overcome friction resulting in wasted energy and reducing the efficiency of machines
  • Friction results in input being lost as heat
  • Friction varies directly in proportion to the weight of the moving parts
  • This means that the greater the weight of the moving parts the greater the greater the friction
  • Friction is not affected by the area of contact between the moving parts
  • Friction is higher between rough surfaces than on smoother surfaces

Reducing friction

  • Popular methods of reducing friction include:
  • lubrication and
  • rolling friction and ball bearings


Lubrication is another way of reducing friction. Image credit skf.com

Lubricating grease. Image credit skf.com

  • This is when a lubricant is used to reduce friction between the two surface layers
  • A lubricant is a long-chain hydrocarbon molecule which maintains a surface layer even under great pressure
  • An example of a lubricant is grease
  • When lubricated the two solid layers slide more easily over one another
  • The surfaces are kept apart by a thin layer of lubricant
  • Heat from a machine e.g. an engine can cause the engine to “seize” and stop working
  • Different engines therefore have various oiling systems to ensure smooth running

Rolling friction and ball bearings

Roller bearing. Image credit bicycles.stackexchange.com

Roller bearing. Image credit bicycles.stackexchange.com

  • When one body rolls over another the friction is much less than when they slide over each other
  • The effort required to push a car is much less when its wheels are turning
  • Compared to trying to push it when its wheels are locked (e.g. when the breaks are applied)
  • Ball bearings and roller bearings are used to reduce friction in various moving parts
  • Such as in engines and wheels

NB In reality both methods are used wherever possible for example grease is  applied to bearings

To access more topics go to the Combined Science Notes page