• Force: Meaning; Types and Uses of Force
  • Calculation of Gravitational Force
  • Friction: Balanced and Unbalanced Forces
  • Gravitational Force and Weightlessness
  • The Earth in Space
  • Space Travel
  • Satellites
  • Basic Science Upper Basic 7 Third Term Examination (Mock)






  1. Definition of Force
  2. Mathematical Expression of Force
  3. Types of Forces
  4. Differences between Gravitational Force and Magnetic Force
  5. Uses of Force


Definition of Force

Force is any action that moves an object or alters its uniform motion in a given direction. Force is the product of mass of the objects and its acceleration. The greater the mass of the object, the greater the force required to move it. Examples of force are pull, push, tension forces and frictional force between surfaces. Force is measured in Newton.

Mathematical Expression of Force

F ά mass × acceleration

F = ma, where m = mass and a = acceleration due to gravity

Types of Forces

There are two types of force. These are;

  1. Contact force
  2. Non-contact force/force field

Contact Force

These are force whose sources are in contact with the body to which they are applied. This occurs between two bodies making contact with each other. The contact can be Direct or Indirect. Examples of direct contact force are push and friction while indirect contact forces are pull and tension. E.g. pushing a car, pulling a table, etc.


Non-contact Force/Force Field

Force field is a force whose source does not require contact with the object to which it is applied. It occurs between two bodies or objects that are separated by Space. Examples are Magnetic

force, Gravitational force and Electric force.

Magnetic Field

A magnetic field gives a magnet its pulling power, called magnetism. This picture shows fragments of metal sticking to the ends of a magnet. The magnetic field of this magnet is strongest at its ends.

Magnetic Force

This is a force that exists around magnet. Objects like iron, pin and nail are attracted by the magnetic force if brought within the magnetic field.

Gravitational Force

Is the force with which the earth pulls all objects towards its centre. It is also called force of gravity. If a piece of stone and feather are allowed to fall at the same time, the stone reaches the ground first. This means that rate of force depend on body weight or mass.

Electric Force

This is a force that exists between two electric charges. Unlike charges attract each other. While like charges repels each other. A repulsive electric force exists between either two positive charges or two negative charges.

Uses of Force

The following are the uses of force:

  1. It is needed to make objects move
  2. It prevents car wheels from slipping on a tarred road when moving on it.
  3. It makes it possible for the car to stop or slow down when the brakes are applied.
  4. Friction between the sole of our feet and the ground makes it possible for us to walk without slipping.
  5. Magnetic force is used by watch repairers to pick tiny iron materials like pin, and screws.
  6. Magnetic force is applied to separate iron dust from solid non-magnetic substances like Sulphur and Sand.



  1. What is a force field?
  2. Explain with examples the two types of force field.





  1. Definition of Gravitational Force
  2. Calculation of Gravitational Forces


Definition of Gravitational Force

This is the force with which the earth pulls all objects towards its centre. It is also called force of gravity. The instrument used for measuring gravitational force is called spring balance.

Calculation of Gravitational Forces

The unit of force is Newton (the symbol is N). The unit was named after Sir Isaac Newton who first discovered the facts about gravity. The weight of a body is the force the earth exerts on it. All forces are measured in Newton. On the earth surface the universal value of acceleration due to gravity (g) is 9.8m/s2 or 10m/s2

To calculate gravitational force (Gf). The following formulae are used:

  1. F = mg, used for calculation of gravitational force.

Example 1: Calculate the gravitational force required to pull down a mango fruit of 10kg falling with acceleration of 5m/s2.


F = mg, where F is unknown, m = 10kg, a = 5m/s2

∴ F = 10 × 5 = 50 N.

Example 2: A mass of 300g is acted upon by a force which produces an acceleration of 5m/s2. Calculate the force.


F = mg,

Since mass is not given in  kg, convert it to kg,

Mass = 300/1000 = 0.3 kg

∴ F = 0.3 × 5 = 1.5N


  1. Work done is defined as the product of force and the distance covered by the object.

Work done = force × distance

Wd = f × h where f = mg

∴ Wd = mgh

Work done = mgh used for calculation of work done against gravity, measured in joules. (J)

Where m = mass of the object measured in kilogram (Kg)

g = acceleration due to gravity measured in meter per seconds square (m/s2)

h = height of object measured in meter (m)

Example 3: What is the work done by a man who lifts a block of 30kg through a height of 3 meters? (g=10m/s2).


Work done = mgh where g = 10m/s2, m = 30kg, h = 3m

:. Work done = 30 × 10 × 3 = 900 Joules

Example 4: If a load of mass 12kg is raised up to a height of 40m. What is the work done in the process? (g=10m/s2)


Work done = mgh

W = 12 × 10 × 40 = 4800 Joules

Example 5: What is the work done when a force of 50N is applied to throw up a stone across a height of 5m.


Work done = force × distance since f = 50N, distance = 5m

Wd = f × h = 50 × 5 = 250 Joules.



  1. If you lift an object from the surface of the ground, you do work in opposing gravity. Suppose you lift an object of mass 2kg from the ground to height of 2m, what is the work done in lifting the object? (g=9.8m/s2)





  1. Meaning of Friction
  2. Uses and Advantages of Friction
  3. Disadvantages of Friction
  4. How to Reduce Friction
  5. How to Reduce Friction
  6. Balanced and Unbalanced Forces


Meaning of Friction

The force that tries to stop a body from moving is called friction. Friction also means force that opposes motion. Friction can be reduced by lubrication i.e. adding oil and grease placed between the two surfaces in contact. The oil and grease are called lubricants.

Protection from Friction

Friction is a force that occurs when one object moves against another. The ceramic tiles on the outside of the space shuttle protect it from the great friction caused when the shuttle re-enters Earth’s atmosphere.

Uses and Advantages of Friction

The following are the uses and advantages of friction:

    1. It enables us to walk and run without slippery
    2. It enables us to sharpen knives and cutting tools
    3. It is a useful force when we tie shoe lace
    4. It is a useful force when we strike a match or sit on a chair
    5. Screw, nails, bolt and nuts rely on friction to prevent them from working loose.

  1. Friction is a useful force in belt drive and clutches on machinery, as it allows energy to be transferred.
  2. Friction makes cars to move on the road. The tyres of a car have rough surfaces so that when the engine of the car makes the wheels go round, they grip on the surface of the road. If tyres and roads were so smooth there will be no friction between them, the car would not move.

Disadvantages of Friction

The following are the disadvantages of friction:

  1. It causes wear and tear on the moving parts of machines.
  2. It causes unpleasant sound (noise).
  3. It increases the cost of maintenance.
  4. It causes heat in any engine which can lead to break down of the engine.
  5. It increases the energy required to operate machine.
  6. It reduces the efficiency of machine.

How to Reduce Friction

Friction is reduced by application of greases and oils called lubricants. Lubricant is placed between the two surfaces in contact.

Balanced and Unbalanced Forces

If a body is at rest, it means that all the forces acting upon it are equal and opposite. This is a balanced force.

But on the other hand if the forces acting on it are not equal the forces are unbalanced, the body will move in the direction of this unbalanced force.




  1. Define friction.
  2. State the advantage and disadvantages of friction.






  1. Meaning of Gravitation
  2. Effect of Gravitation on Objects
  3. Weightlessness


Meaning of Gravitation

Gravitation is a type of force that acts on a body across a distance, without any contact between the source and the body.

The earth exerts a gravitational force on bodies by which it pulls these bodies towards its centre. This is why fruits fall to the ground from the tree and do not rise upwards. Also, when a stone is thrown upwards it soon stops its upward movement and starts to fall back to the earth.

The force of gravity is a universal force. It exists between the earth and bodies and between planets and stars.

Gravitational pull determines the weight of objects.

The amount of force with which gravity pulls an object depends on three things, namely:

  1. The mass of the object.
  2. The mass of the earth.
  3. The distance between the centre of the object and the earth.

Effect of Gravitation on Objects

  1. Gravitation gives objects weight.
  2. Gravitation keeps the earth and the other planet in their orbits around the sun.
  3. Gravitation keeps the moon in its orbits around the earth.
  4. Gravitation keeps the moon in its path in the sky.
  5. It is the work against gravity that make aeroplanes to fly in the sky.
  6. Gravitation bring about the formation of tides, for convection (by which hot fluids rise)


The term weightlessness is described as a state of not experiencing the effect of gravity. Astronauts in space experience weightlessness. It does not mean that they do not have weight but they will just feel as if they are weightless. Weightlessness is felt in space and the moon. The weight of an object in the moon is one sixth (1/6) of the weight of the object on earth. If an astronaut weighs 60N on earth, in the moon he will weigh 10N.

Lesson Notes / Scheme of work

Primary 1  |  Primary 2Primary 3

Primary 4 |  Primary 5Primary 6



Question Bank

Primary 1 |  Primary 2  |Primary3

Primary 4  | Primary5 Primary6



Lesson Notes

Primary School lesson notes, all subjects.

Lesson notes

Lesson  notes and plan for secondary schools

Question Bank

Question bank for primary

Question Bank

Question Bank for Secondary School

work sheet

Worksheet for all levels

If you need all the content at an affordable price (N500) ONLY, feel free to contact us.

+2348039740135 : whatsapp

Are you a school owner or a teacher,

Click the image below to join Teachers’ Connect to learn more…



You cannot copy content of this page

error: Content is protected !!
Advertise with us