• Friction                                         Force
  • Nuisance                                       Moments
  • Mechanical advantage                 Wedges
  • Inclined Plane                                Axles
  • Screws



  • Is the force that opposes movement of objects.

Types of friction
1. Static friction
: It is found in objects which are fixed in one position.
2. Sliding or rolling friction: It is found in moving objects.
3. Viscosity friction: This occurs in liquids and gases.

Properties of friction.
i.There is more friction with rough surfaces than with smooth or slippery ones.
ii.The greater the load, the greater the friction force (weight increases friction)
iii.Whenever friction occurs heat is produced.

Friction as a useful force in our daily life.
1. It helps in moving and stopping vehicles.
2. It helps when writing.
3. It helps when sharpening objects.
4. It helps when walking.

5. It helps in lighting match sticks.
Friction as a nuisance force/ disadvantages.

1. It wears away things e.g. shoe soles, parts of engines.
2. It hinders work as it makes us use a lot of force.
3. It produces unnecessary heat and noise.

How to increase friction.
i. Making smooth surfaces rough.
ii. Putting treads on vehicle tyres /  on shoe soles.


iii. Putting spikes on sports boots.
iv. Putting grips on handles of bicycle.

How friction can be reduced.

i. Using rollers; they decrease areas of contact between moving parts.

ii. Using ball bearings; these are round metallic balls they reduce friction by keeping moving parts separated.

ball bearing

iii. Lubricating; This involves using oil or grease.
Oil and grease are referred to as lubricants.
iv. Stream lining objects like planes, cars

v. Making rough surfaces smooth.


  1. State a brief meaning to the term friction.
  2. In one way explain how friction can be increased on a slippery surface.
  3. Write down any two advantages of friction in our lives.
  4. Why is friction said to be a nuisance force?
  5. Why are some objects stream lined?
  6. State any two items that are stream lined?