Force - Definition, Examples, Unit, Characteristics, FAQs

The force is a fundamental concept in physics that represents an interaction which causes changes in the state of motion of objects.Forces are essential in understanding and predicting physical phenomena. Force can cause an object to accelerate, slow down or change direction of motion. The article could cover different types of forces such as gravitational force , normal force, frictional force, tension forces etc. Additionally, the article might include characteristics of force and its practical examples in everyday activities.

Understanding Force: The Basics

The term Force means the push or pull, an external agent which has the ability to change the state of a body. If a body is applied by some external force it can bring a moving body into rest as well as Force can bring a body at rest into motion. S. Isaac Newton introduced the concept of Force in his famous book Principia Mathematica 1687.

Define Force:

Force is an external applied agent to a body which has the tendency to change the state of motion of a body. Mathematically, Force acting on a body is defined as the rate of change in momentum of a body.

Force Equation:

Mathematically, The formula of force is written as

$F=ma$

where,

• m is the mass of the body
• a is the acceleration of the body.

This equation $F=ma$ is known as the Force equation.

Also read :

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Applications of Force In Everyday Life

Some of the most common examples of force in everyday life are:

1. When we hit a ball with the bat while playing sports, the ball moves in a particular direction due to the force acting on it by the bat.

2. When we push a door, it changes its position and gets opened or closed and this is due to force acting on it with our hands on it.

S.I Unit and Dimensional Formula of Force

• The S.I unit of Force is Newton, named after scientist S. Isaac Newton denoted by N.
• 1N is defined as the force acting on a moving body having an acceleration of $1{\mathrm{ms}}^{-2}$ and having mass of 1Kg. And in CGS unit system the Unit of force is ${\mathrm{gcms}}^{-2}$
• The dimensional formula

We know that , $F=ma$

dimensional formula of $[m]=[M]$

dimensional formula of $a=\frac{v}{t}=\frac{[L]/TT]}{TT}=\frac{[L]}{[T{]}^2}$

Substituting these in the equation, we get

$[F]=[M]\cdot \frac{[L]}{TT{]}^2}$

Dimensional formula of force is ,

$$[F]=[M][L][T{]}^{-2}$$

Different Types of force

Mainly, Force can be categorized into two types namely;

1. Contact Forces
2. Non-Contact Forces

NCERT Physics Notes:

• NCERT Notes Class 11th Physics
• NCERT Notes Class 12th Physics
• NCERT Notes For All Subjects

Differences Between Contact and Non-Contact Forces

Various types of Contact Force:

1. Force acting on a rope, Tension Force
2. Force acting on a spring, Spring Force
3. Frictional Force
4. Force due to Air resistance
5. Normal Force
6. Applied Force

1. Force acting on a rope, Tension Force

When we pull a rope or string or any cable, the force acting on the rope in the direction of its length is called Tension force. Its denoted by T. If a rope is released from a pulley and rope is moving downward with acceleration a and mass m then tension force is written as

$$T=ma+mg$$

2. Force acting on a spring, Spring Force

Whenever a spring is stretched to some length, spring always has a restoring force to bring it on its original state, and such restoring force is called spring force which is calculated by famous Hooke’s law as

$F=-Kx$

where,

• x is the distance to which spring is stretched
• k is spring constant and negative sign shows that spring force is a restoring force.

3. Frictional Force

When two bodies are in contact and tend to slide over each other, then the force which opposes the relative motion between two bodies over their contact is called Frictional force.

Frictional force is mainly of two types:

The types of frictional force is given below with explanations.

4. Force due to air resistance

When a body is moving through the atmosphere then the particles of the air come in contact with the moving body, hence opposing the motion of the body in the air, such type of resistance forces produced due to air is known as Air resistance. Also, when a body moves in a fluid like water then opposing force due to water or any fluid is known as retarding force.

5. Normal Force

When two bodies are in contact with each other then, the force normal to the surface of contact is called normal force, For example, if an object is placed on a table then, force on the object perpendicular to the table is called the normal force.

6. Applied Force

As the word suggests, the applied force is considered when a body applies some force on any other body which brings a change in direction or velocity of the body, such forces are called applied forces.

Applied Forces are mainly of three kinds:

• Push: When we push an object to change its position, such as pushing a door to open or close in everyday life, it is an example of applied force.
• Pull: When we pull some object such as pulling a rope over a pulley is an example of applied force.
• Drag: When a body is moved against any other body such as a body moving in fluid or in air, such retarding forces acting on the body to oppose its relative motion are examples of air drag and fluid drag forces.

Various Kinds of Non-Contact Forces:

1. Gravitational force
2. Electrostatic force
3. Magnetic force

1. Gravitational Force

It was first S. Isaac Newton who gave the concept of Gravitational force and it is defined as the attraction force acting between two bodies that have mass and are separated by some finite distance and this force act on every object in the universe. Mathematically, if two bodies have mass m₁ and m₂ and are separated by a distance of r then Gravitational force F is calculated as

$$\mathrm{F}=\frac{\mathrm{G}{\mathrm{m}}_1{\mathrm{m}}_2}{{\mathrm{r}}^2}$$

where,

G is called Gravitational constant which has a fixed value of $\mathrm{G}=6.67\times {10}^{-11}{\mathrm{Nm}}^2{\mathrm{Kg}}^{-2}$

Also read -

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2. Electrostatic Force

It was Coulomb, who introduced the concept of electrostatic force. The force acting between two static charged particles having definite charge magnitude and separated by some finite distance is called electrostatic force. Mathematically, if two charged particles have charges q₁ and q₂ and are separated by distance r then electrostatic force F is calculated as

$$F=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{r^2}$$

where,

${\epsilon }_0=8.854\times {10}^{-12}{\mathrm{C}}^2/{\mathrm{Nm}}^2$ is known as permittivity of free space.

3. Magnetic force.

If a charged particle is moving in a uniform magnetic field then, the charged particle experiences a force due to the presence of a magnetic field and such forces are called magnetic force. Mathematically, if a charged particle is moving with velocity vector v and magnetic field vector is B and the charge has a magnitude of q then magnetic force F is calculated as

$F=q(v\times B)$

Hence, all quantities Force, Magnetic field and velocity are perpendicular to each other.

Causes of Force:

Whenever a body experiences a force on it, it changes its state of motion such as a moving body comes at rest or increases or decreases its velocity when a body at rest starts moving. Every force has its cause and various most common force experiences cause are listed as:

1. Falling of a body. Whenever a body falls, it experiences a force and the cause of this force is gravity which is due to the gravitational pull of the earth towards the body.
2. Bending of a moving charged particle in presence of the magnetic field. The magnetic field is the cause of force experienced on a moving charge particle and hence changes its direction in presence of magnetic field.
3. To push an object away from the body and to pull an object towards the body is the main cause of force experienced on the body.

Characteristics of Force:

Some of the main characteristics of force are listed as:

1. Force brings the change in velocity or direction of a body, when the applied body may experience a change in its velocity or change in its direction. For example, when we apply some force on a stationary body, it gets some velocity and changes its position.
2. Force is always defined by two parameters, one is magnitude such that it will always have some definite magnitude and as well as a particular direction. For example, a body moving in a circular path experiences a centripetal force that has definite value and direction always towards the centre.
3. If a body is at rest then it means all the net forces acting on it are zero and forces are added using rules of vector algebra.
4. Force applied to a certain area creates pressure.
5. Force can change the shape of an object by producing stress on the object.
6. When two forces act on an object, the net force is

• Sum of the forces if the forces acts in the same direction
• Difference of the forces if the forces act in the opposite direction

7. Line of Action:

The Line of action simply means the line which follows the applied force on a body. A line of action is a geometrical line passing through the point where force is applied and it has the direction always in the direction of the Force.

Also check-

• NCERT Exemplar Class 11th Physics Solutions
• NCERT Exemplar Class 12th Physics Solutions
• NCERT Exemplar Solutions for All Subjects

Summary

Force is an external effort in the form of push or pulls ,which (i)tries to produce motion in a body at rest, or (ii) tries to stop a moving body, or (iii)tries to change the direction of motion of the body.Force is a vector quantity.We learnt briefly about types of forces: from gravty to electromagnetsim with examples in this article.