# What is Force in Physics-definition,types

Sometimes a question comes to our mind what is a force in physics? In our daily life, we experience a force whenever we do work on an object. When we do work on an object either by pushing, pulling, or holding, we experience a force.

What is Force in Physics for Class 11th and 12th Students

## Introduction

Force is the phenomenon that we experience either by pushing, pulling, or holding an object. For example, if you push an object, you exert a force that is away from yourself. Similarly, if you pull an object you experience a force that is towards yourself.

When you hold an object which is heavy, you experience a great amount of force which may cause changes in the shape or deformation of an object. So force is a natural phenomenon. Detail knowledge of what is the force in physics

## Definition of Force

Force is defined as the interaction between two objects that tends to maintain or alter the motion of an object or distort it. In other words, it can be defined as the external source which has the capacity to change the state of rest or motion of a particular object.

## Formula

The symbol of force is F

 F=mass. acceleration= m.a

F can be also defined as:-

 F=mass x velocity/ total time taken=mass x length/time²=mass x length x time -2

Where, Velocity (V)= displacement/total time=length/time

In SI unit (Standard international unit system) its unit is expressed in Newton

In the CGS system (Centimetre gram second system) its unit is expressed in dyne

SI Base unit: – Kg m s-2

Dimension:- M LT -2

As Force has both magnitude and direction, Force is a vector quantity and its direction is along with the motion.

## Concept of Force in Terms of Motion

The concept of force is commonly explained in terms of Sir Isaac Newton’s law of motion.

Newton’s first law of motion

A body remains at rest or moves with a constant velocity until some external force is applied to it.

OR

A body does not accelerate if the vector sum of all the forces is zero. If we apply external forces which change their position and vector sum of all forces is not zero.

EX: – if a=0 then F=0 and if a ≠0 then F≠0

This law gives the idea of inertia.

Newton’s second law of motion

When external forces act on a body it produces acceleration and its direction is along with force.

In other words, the acceleration of a particle as measured from an inertial frame is given by the vector sum of all forces acting on the particle divided by its mass.

a = F / m

The acceleration is measured by this law.

Newton’s third law of motion

Action and reaction create simultaneously or if a body ‘A’ exerts a force F on another body ‘B’ then ‘B’ exerts a force equal and opposite force (–F) on A. These forces are equal in magnitude but the direction is opposite. Directions of these forces are acting along the line joining the bodies.

Note:-action and reaction depend on our assumption.

This principle of action and reaction explains how a force tends to deform a body (i.e., change its shape) and whether or not it causes the body to move.

## Effect of force

From the above concept of motion we have seen that due to force on a body (or an object), motion can be described in the following ways:-

1. It can make a movement of the body that is at rest in a position
2. It can stop or slow down the moving object
3. It can accelerate the movement of a body whose direction is along with the force
4. Force can also change the direction of the moving body which can further distort of moving body.

## Types of force

A force is a physical cause that can be seen during changing in the state of motion or dimension of an object. This is the basic concept of what is force in physics.

Based on application, a force can be divided into two types:-

1. contact force
2. non-contact force

### Contact Force

We can create a force on objects either directly or through any medium. In this type of force, the interaction of two objects touches each other.

Examples: – Muscular force, Frictional force, Mechanical force

Muscular force:-If we use our muscles for any activity. Lifting weight, pushing, or pulling an object using our muscles and others are some examples. Mechanical force:-If we use other sources for any activity.

Example:-pooling of objects using rope is the best example.

Frictional force:-

A force that acts on pair of two surfaces in contact and one surface opposes the motion of the other surface.

Example:- Object that slides on a rough surface.

### Non-contact force

In this type of force, there is no direct contact between two objects. In other words, if a force that acts through spaces without making direct contact with the objects is called a non-contact force.

Examples:- Gravitational force, Electrostatic force, Magnetic force

Gravitational force

It is the attraction of two objects by virtue of their masses and there is a certain distance between them.

Example:- Falling of an object from a certain height is due to the strength of gravity of the earth.

FG = G M m1r² where FG is the gravitational force, M and m1 are masses of earth and an object. The value of G is 6.67 X 10‾11N-m²/kg² called the gravitational constant. The direction of FG is towards the center of the earth which is called along the vertically downward direction.

Electrostatic force

If two charged particles having charges Q1 and Q2 are stationary and kept at a certain distance d.

Then, electrostatic force, FE = Q1Q2/4πε0 d²

The value of 1/4πε0 is 9.0 X 10⁹ N-m²/C²

Where ε0=8.854x 10‾12 C²/N-m² is a constant. This is also called the Coulomb force. Here there are no direct contacts between two charged particles but there is spacing between them. In this type, force is either repulsive or attractive.

Magnetic force

It may also be either an attractive or repulsive force that arises due to electrically charged particles that are in motion. If we place two Magnets at a certain distance they may attract each other or repel each other depending on the North Pole and the South Pole. Nuclear force

We know that matter is composed of electrons, protons, and neutrons. Protons and neutrons have positive and neutral (or no charges) respectively. The nucleus of an atom contains protons and neutrons. Electrons having charges 1.6X10-19 C revolve around the nucleus. In an atom, electrons are bounded by electromagnetic force acting on them due to the proton.

But one thing that is important is that there is a nuclear force that exists between protons and neutrons due to which protons and neutrons are bounded together. These forces exist between protons and protons, protons and neutrons, and neutrons and neutrons. These forces hold the nucleus together called Nuclear force.

Some key points:-

1. Gravitational force is the weakest force as its gravitational constant value is very small
2. The nuclear force is the strongest force which is 100 times stronger than the electromagnetic force.

## Conclusion

From the above discussion, we have seen that force changes the state or position of rest or motion and changes the direction and magnitude of a particular object. It also changes the direction of a movable object along with the shape and size of an object. This gives an idea of what is force in physics.