4p1 Force


  Force is a pull or push of a body.Force can cause a  body to stop. 
Force can cause a body at rest to start moving.
Force can change the size and shape of an object.
Force can affect direction and the speed of a moving body.

The SI unit of force is the Newton (N) 


 There are four types of fundamental forces which are;

  1. Gravitational forces- Is the force of attraction between bodies in the universe. An example is the earth’s gravity which pulls objects towards earth’s centre.
  2. Strong forces- These are forces responsible for binding nuclei of an atom. They hold the nucleus together (neutron and proton)
  3. Weak forces – Is the force responsible for various trends of  radioactive decay. The decay of fundamental particles such as Beta particles.
  4. Electromagnetic  forces- Is the force which cause magnetic and electrical effect.


  1. Define the term force and state its SI unit.
  2. What can force do?
  3. List four types of force
  4. Distinguish between stretching force and restoring force. Give one example of each force                      
  5. What do you understand by the weight of a body?

Effect of forces include;

1. Stretching and restoring

2.Compressional and restoring

3. Attraction

4. Repulsion

5. Torsion


7. Viscosity

8. Air resistance

Stretching and Restoring
Stretching occurs when an object increases its length when the force is applied to it. For some objects there is a tendency to return to their original shape and size. This is called restoring force.

Compressional and Restoring

 Compressional force is the force when applied to an object results in decrease in its volume. If the body returns to its original shape and size it is called restoring force.

Is the force by which one object attracts another for example a magnetic exerts an attractive force on a piece of metal.

This is the force of separation that a body or particle exerts on another.

Example when the like poles of two magnets are brought near each other.

Viscosity is the force which resist flow of fluid we may call it the liquid friction.

Torsional force
This is produced when a solid object is twisted, if this object return to its original shape then it is called restoring force.

Air Resistance
Is the force which resists the movement of an object through air.

Friction Force
Is the force which opposes motion of a moving body whenever one object slides over another object, friction tries to stop the movement.

The weight of a body is the attractive force towards the earth’s centre exerted by the earth on the body.

Formula for weight
Weight=Mass × Gravitation Acceleration


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