Force - Definition, Examples, Unit, Characteristics, FAQs

What is Force in Physics

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

Force Formula

Mathematically, the formula for 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.

Forces Applications 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 the force acting on it with our hands.

S.I. Unit and Dimensional Formula of Force

• The SI unit of Force is Newton, named after the scientist Sir Isaac Newton, denoted by N.
• 1N is defined as the force acting on a moving body having an acceleration of 1 $\mathrm{m} / \mathrm{s}^2$ $\mathrm{m}/{\mathrm{s}}^2$ and having a mass of 1 kg. And in the CGS unit system, the Unit of force is $g \frac{c m}{s^2}$ $g\frac{cm}{s^2}$.

The dimensional formula

We know that F = ma

dimensional formula of [m] = [M]

dimensional formula of a = vt = $\left[L{T}^{-2}\right]$

Substituting these in the equation, we get

[F] = $\left[\mathrm{M} L \mathrm{~T}^{-2}\right]$$\left[\mathrm{M}L{\mathrm{T}}^{-2}\right]$

The dimensional formula of force is,

[F] = $\left[\mathrm{M} L \mathrm{~T}^{-2}\right]$$\left[\mathrm{M}L{\mathrm{T}}^{-2}\right]$

Types of Forces With Examples

Mainly, Force can be categorized into two types, namely;

1. Contact Forces
2. Non-Contact Forces

Differences Between Contact and Non-Contact Forces

Various types of Contact Forces:

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 the Tension force. It is denoted by T. If a rope is released from a pulley and the rope is moving downward with acceleration a and mass m, then the tension force is written as

T=ma+mg

2. Force acting on a spring, Spring Force

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

F=−Kx

where,

• x is the distance to which the spring is stretched
• k is the spring constant, and the negative sign shows that the 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 that opposes the relative motion between two bodies over their contact is called the Frictional force.

The frictional force is mainly of two types:

The types of frictional forces are 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. This type of resistance force 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, the force normal to the surface of contact is called the normal force. For example, if an object is placed on a table, then the 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 the 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 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
4. Nuclear force

1. Gravitational Force

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

$F_g=G \frac{m_1 m_2}{r^2}$

where,

G is called the Gravitational constant, which has a fixed value of G=6.67×10⁻¹¹ $\frac{\mathrm{N} \cdot \mathrm{m}^2}{\mathrm{~kg}^2}$.$\frac{\mathrm{N}\cdot {\mathrm{m}}^2}{{\mathrm{kg}}^2}$

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 the electrostatic force. Mathematically, if two charged particles have charges q₁ and q₂ and are separated by a distance r, then the electrostatic force F is calculated as

$F=k \frac{q_1 q_2}{r^2}$

where,

${\epsilon }_0$ $\varepsilon_0$ = $8.85 \times 10^{-12} \mathrm{C}^2 / \mathrm{N}-\mathrm{m}^2$ $8.85\times {10}^{-12}{\mathrm{C}}^2/\mathrm{N}-{\mathrm{m}}^2$is known as the 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 forces. Mathematically, if a charged particle is moving with velocity vector v, and the magnetic field vector is B, and the charge has a magnitude of q, then the magnetic force F is calculated as

F=q(v×B)

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

4. Nuclear force

Nuclear force is the fundamental force that binds protons and neutrons (nucleons) together within the nucleus. This nuclear force holds the protons or neutrons together despite their charges are similar in nature.

Nuclear force is of two types:

• Weak nuclear force- This force plays an important role in nuclear fission. This force is responsible for Radioactive decay, like beta decay.
• Strong nuclear force- It is the strongest force that exists in nature. This force is responsible for the binding of two similarly charged atoms, but its range is the smallest (up to a few angstroms).

Causes of Force

Whenever a body experiences a force on it, it changes its state of motion, such as a moving body comes to 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 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 the presence of a magnetic field. The magnetic field is the cause of the force experienced by a moving charged particle and hence changes its direction in the presence of the 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 force 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 as well as a particular direction. For example, a body moving in a circular path experiences a centripetal force that has a definite value and direction always towards the center.
3. If a body is at rest, then it means all the net forces acting on it are zero, and forces are added using the rules of vector algebra.
4. The 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

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

Line of Action

The Line of action simply means the line that 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.

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