Friction is the force that opposes motion.

          Properties of friction

1.       Rough surfaces produce more friction than smooth surface.

2.       Heavy bodies produce more friction than the light one.

3.       Sliding friction is smaller than rolling friction.

          Friction as a useful force.

  1. It enables us to write using pens, pencils chalk, etc.
    1. It enables brakes of vehicles to stop movement.
    1. It helps in lighting a match stick.
    1. It enables forward movement of vehicle tyres.
    1. It was used by early man to produce fire.
    1. It is used in sharpening tools.
    1. It enables plant roots to hold the plant firmly in the soil.
    1. It enables us to walk without sliding.
    1. It enables us to hold objects tightly.

How to increase friction.

  1. Making surfaces rough  through;

i) Applying sand or stones between surfaces.

ii) Increasing the weight of the object.

iii) making trades on car tyres.


v) Putting spikes on shoes to increase on friction.


          Friction as nuisance

  1. It causes things to wear off.
    1. It causes unnecessary noise in machines.
    1. It produces unnecessary heat in machines.
    1. It delays work.
    1. It makes us do little work after applying a lot of energy.

How to reduce friction.

Friction can be reduced by:

  1. Oiling the moving parts of the machine.
  2. Greasing the moving parts of the machine.
  3. Using rollers and ball bearings.
  • Reducing the weight of objects.
  • Making rough surface smooth.
  • Synovial fluids in joints reduce friction.
  • Streamlining bodies to reduce friction in water and air.


1.       Viscosity is friction in air or water.

2.       Viscosity is reduced by streamlining the machine that move in water and air.

3.       Some animals that dwell in water and air are streamlined bodies to reduce viscosity.

          Animals streamlined to reduce viscosity.

  1. Fish
  2. Birds
  3. Crocodiles
  4.  Snakes
  5. Earthworms
  6. Cheetah or Leopard
  7. Whale

          Streamlined machines to reduce viscosity.

  1. Boats
  2. Canoes
  3. Marines
  4. Spears
  5. Arrows
  6. Rockets and jets.
  7. Aero planes