Definition of Force- Types, Formula, and Units

Let’s start with the introduction of “Definition of Force”.  This article will be discussed in detail about definition, formula, unit, and types of force.

Definition of Force

The definition of Force- Force is a push or pulls acting upon an object as a result of its interaction with another object. It is used in our everyday activities like stretching, twisting, pushing, pulling, lifting, and pressing. For example, a force is used when we push or kick a ball; a force is used when we pull the drawer of a force is used when we twist a wet cloth to squeeze out water.

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Definition of Force

Effect of Force

  • Force can move a stationary object.
  • It can stop a moving object.
  • It can change the speed of a moving object.
  • A force can change the direction of a moving object.
  • A force can change the shape and size of an object.


Types of Force

There are a variety of forces placed into two broad categories on the basis of whether the force has resulted from the contact or non-contact force.

Contact force

Forces that act between the objects when the objects are in contact with each other.


Examples of Contact Forces

  • Applied force

The applied force is a force applied on an object by a person or another object. If a boy pushes a desk across the room or hammers a nail, then there is an applied force acting upon the object.

  • Air resistance force

It is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object.

Air resistance force will frequently be neglected due to its negligible magnitude. It is most noticeable for objects that travel at high speed (like skydiver or a downhill skier) or for an object with large surface areas.

  • Tension Force

It is the force that is transmitted through a string, rope, cable, or wire when it is pulled tight by forces acting from opposite ends. It is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire.

tension force


  • Spring Force

It is the force exerted by a compressed or stretched spring upon any object that is attached to it. An object that compresses or stretches a spring is always acted upon by the force that restores the object to its rest or equilibrium position. For most springs magnitude of the force is directly proportional to the amount of stretch or compression of the spring.

spring force

  • Normal Force

The normal force is the support force exerted upon an object that is in contact with another stable object. For example, if a notebook is resting upon a surface then the surface is exerting an upward force upon the notebook in order to support the weight of the notebook. On occasion, a normal force is exerted horizontally between two objects that are in contact with each other. For instance, if a boy leans against a wall, the wall pushes horizontally on the boy.


  • Frictional Force

It is the force exerted by a surface as an object moves across it or makes an effort to move across it. Frictional force often opposes the motion of an object.


Non-contact forces

The force which acts on an object without coming physically in contact with it is called non-contact force. All four known fundamental interactions are non-contact forces.


Examples of non-contact Forces

  • Gravity and Gravitational Force

Gravity is a force of attraction which is exerted on all bodies that have mass. The force exerted on each body by the other through weight is proportional to the mass of the first body times the mass of the second body divided by the square of the distance between them.

This force actually refers to the weight of the object. All objects upon the earth experience a force of gravity that is directed downward towards the centre of the earth. The force of gravity on the earth is always equal to the weight of the object as found by the equation:

   F = m X g

  Where g=9.8 N/kg on the earth and “m” is mass in kg.

  • Magnetic force

A magnet can extract a force on another magnet without being in contact with it. Like poles of 2 magnets repel each other and unlike poles attract each other.



  • Electrostatic force

Two like charges repel and two unlike charges attract each other, the force between these charges is known as electrostatic force.



  • Electromagnetism

It mediates all chemical, biological, electrical, and electronic processes. It is the force that causes the interaction between electrically charged particles; the area in which this happens is called electromagnetic fields.

Examples of this force include electricity, magnetism, radio waves, microwaves, infrared, visible light, X-rays, and gamma rays.

  • Nuclear Force

The force acting between nucleons is known as nuclear force. It is the strongest force in nature.

  • It is a very short-range attractive force.
  • The nuclear force is a non-conservative force.
  • It is neither gravitational nor electrostatic force.
  • It is independent of charge.
  • The nuclear force is 100 times that of electrostatic force and 1038 times that of gravitational force.

Types of Nuclear Force

  1. Strong Nuclear Force

Unlike gravity and electromagnetism, the strong nuclear force is a short distance force that takes place between fundamental particles within a nucleus. The strong nuclear force is charge independent and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron.

The strong nuclear force is the strongest force in nature. It mediates both nuclear fission and nuclear fusion reactions.

  1. Weak Nuclear Force

Weak nuclear force mediates the decay of a neutron, in which the neutron decays into a proton and in this process emits a  particle and uncharged particles called a neutrino. As a result of mediating the decay process, the weak nuclear force plays a key role in a supernova. Both these strong and weak forces form an important part of quantum mechanics.


What is Torque or Moment of a Force?

The turning effect of a force about a point or a line is called the moment of a force about that point or line which is called exist of rotation. The turning effect of a coerce is dependent on the magnitude of the force and the perpendicular distance of its line of action from the axis of rotation.

The force turns or tends to turn the body either in the clockwise or anticlockwise direction. The direction of the moment of force is fixed by the direction in which the force turns or tends to turn the body.

The anticlockwise direction is considered as a positive direction of the moment of a force. For the larger magnitude of the force, there must be a large turning effect and its moment of force. Thus turning effect is too much appreciable for a larger moment of force and its perpendicular distance from the axis of rotation.

The moment of the force is defined as the product of the force and the perpendicular distance from the axis of rotation.

 Moment of force = Force X perpendicular distance from the axis of rotation

Moment of force,  = F x r x sinθ

  Where,  is the angle between the force and the position vector. The moment of a force or Torque is a vector quantity and its S.I. unit is N-m.


Two equal and opposite forces form a couple and it is defined as the product of the force and the couple arm.

      Couple = Force x couple arm

                 = F x d

A couple is a vector quantity that appears like torque and its SI unit is N-m. The effect of applying a torque or couple on a body is always to rotate the body because a couple will always have an unbalanced moment about any point or an axis of rotation.


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My Name is Mukesh Kumar. I am a Teacher, Blogger, Educational Content Writer, and Founder of CBSE Digital Education.

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