According to Newton's first law of motion which states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force .

Force can be defined as an agent that can cause a body to change its state of rest or uniform motion in a straight line. Force can simply be defined as an agent that causes a body to move or stop moving. Force enables a body possess inertia. The unit of force is Newton.

One newton can be defined as the force required to cause a mass of 1kg to accelerate by 1m/s².

1. Contact force: This is any force that is applied by objects in contact with each other. The contact force acts on a point of direct contact between the two objects. Contact forces are exerted via contact. Some examples of contact forces include:
   • Air resistance: This is the force exerted on a body when it is falling or in contact with air. For example, a mango fruit falling from a tree experiences air resistance.
   • Tension: This is the force experienced by a body e.g string, ropes, cables after been stretched by an applied force. Tension is a pulling force. For example, a rope holding a ceiling lamp experiences tension.
   • Reaction or Normal force: According to Newton's Third law of motion, for every action there is an equal and opposite reaction. This is a force that acts perpendicular and opposite to an applied force acting on two surfaces in contact. For example, a stone on a table is acted upon by reaction force and frictional force which are acting in opposite directions. $$ R = mg $$
   • Friction:This is a force that tends to oppose relative motion between two surfaces in contact.
   • Push and pull: When a force is applied to move an object away from the force applied, the force applied is a pushing force. When the force moves the object towards the force applied, the force applied is a pulling force.
   • Upthrust: This is a force that pushes an object immersed in a fluid upwards. It causes an object to float in water.


2. Force fields: A field is a region of space in which a body experiences the effect of a force. Force fields are non contact forces which do not require direct contact with objects for their effect to be experienced. Force fields act within a region called fields. Some examples of Force fields include:
   • Magnetic Force: This is the force exerted by a magnet on magnetic substances within a magnetic field.
   • Electric force: This is the force experienced by a charged body in an electric field.
   • Gravitational force:This is the force exerted on a body under the influence of a gravitational field.