# Major Laws of Physics

We all know that Physics can be divided into different fields of studies. These fields of studies include mechanics, nuclear physics, optical physics, atomic and molecular physics, astrophysics, thermodynamics, electrodynamics, and magnetism. All these fields have laws, principles, and theories that govern them. The concepts from these fields become easy to understand when the laws and principles are studied.

In this article, we shall learn some of these laws based on the fields of physics. Also, we shall understand their applications. Below is the list of three fields along with the two laws that we are going to discuss further:

Field |
Laws |

Mechanics | ● Newton’s laws of motion
● Newton’s law of universal gravitation |

Optics | ● Beer-Lambert law
● Raman scattering |

Thermodynamics | ● Laws of thermodynamic
● Ideal gas law |

## Mechanics

Mechanics is one of the fields of Physics that deals with the motion of the bodies under the influence of forces. There are three categories in mechanics and they are:

- Statics: When the force is acting on an object that is at rest
- Kinematics: When a body or system of bodies are in motion
- Kinetics: This is the prediction of the motion of an object in a given situation

### Newton’s Laws of Motion

The laws that helped us in understanding the behaviour of an object when it is at rest when it is in motion, and when there is a force acting on it is explained by **Newton’s laws of motion.** There are three laws of motion and they are:

- Newton’s first law of motion: This law is also known as the law of inertia. The law states that when an object is at rest or uniform motion, the object will continue to be at rest or in uniform motion unless acted upon by an external force.
- Newton’s second law of motion: According to the second law of motion, the force acting on the object is the product of mass and acceleration.
- Newton’s third law of motion: According to the third law of motion, for every action, there is an equal and opposite reaction.

### Newton’s Law of Universal Gravitation

According to Newton’s law of universal gravitation, every particle attracts every other particle in the universe with a force that is directly proportional to the product of the masses and is inversely proportional to the square of the distance between them.

The mathematical representation of the law is:

Where,

- F is the gravitational force between the bodies
- m1 and m2 are the masses of one of the objects
- r is the distance between the centres of the two objects
- G is the universal gravitational constant

## Optics

Optics is one of the branches of physics that deals with light and its behaviour. This behavioural study of light can be done by understanding the properties of light when they interact with matter. Reflection is considered to be one of the primary properties of light. Refraction, dispersion, total internal reflection, polarization are the other properties of light.

### Beer-Lambert Law

According to Beer-Lambert law, the path length of the sample and its concentration are directly proportional to the absorbance of the light. The mathematical representation of the law is:

Where,

- I is the intensity
- I
_{o}is the initial intensity - μ is the coefficient of absorption
- x is the depth in meter

### Raman Scattering

Raman scattering is also known as the Raman effect and is defined as the scattering of photons by the excited molecules when they are at higher energy levels. Raman spectroscopy is one of the applications of Raman scattering. It finds use in fields such as nanotechnology, in medicine, and in chemistry to understand the structure of molecules and their bonds.

## Thermodynamics

The concepts of heat and temperature and their conversion into different forms of energy is studied in thermodynamics. The term thermodynamics is derived from the Greek work *thermes *and *dynamikos *which means heat and power respectively. Following are the branches of thermodynamics:

- Classical thermodynamics
- Statistical thermodynamics
- Chemical thermodynamics
- Equilibrium thermodynamics

### Laws of Thermodynamics

There are four laws of thermodynamics and they are:

- Zeroth law of thermodynamics: This law states that if two bodies are in equilibrium with the third body individually, then the first two bodies are also in thermal equilibrium with each other.
- First law of thermodynamics: According to this law, the energy can neither be created nor destroyed, it can only be changed from one form to another. This law is also known as the law of conservation of energy.
- Second law of thermodynamics: This law states that the entropy of an isolated system always increases.
- Third law of thermodynamics: This law states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

### Ideal Gas Law

According to ideal gas law, it is an equation of a hypothetical system of gas with a good approximation of the behaviour under the conditions that comes with limitations. The **ideal gas law** is given as:

PV = nRT |

Where,

- P is the pressure of the ideal gas
- V is the volume of the ideal gas
- n is the number of moles present in the ideal gas
- R is the gas constant
- T is the temperature

These were some major fields of Physics and laws that fall under them. Stay tuned with BYJU’S for more understanding of other concepts.