Laws of physics play an important and fundamental role in Science. Many laws of physics are built after various research or some are a modification of existing laws and theoretical research.

Physical laws are the conclusions drawn based on the result and conclusion of years of scientific observations and experiments which are repeated again and again under different conditions to reach the assumptions which can be accepted worldwide. We all know our world works on some principles and these principles are drawn by our scientists in the form of certain physical laws. Following are the most important physics laws.

**Archimedes Principle**

Archimedes' principle is a law of physics fundamental to fluid mechanics. It indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and it acts in the upward direction at the center of mass of the displaced fluid.

**Avagadro’s Law**

The law states that two given samples of an ideal gas, of the same volume and at the same temperature and pressure, contain the same number of molecules. In practice, real gases show small deviations from the ideal behavior and the law holds only approximately, but is still a useful approximation for scientists. As an example, equal volumes of molecular hydrogen and nitrogen contain the same number of molecules when they are at the same temperature and pressure, and observe ideal gas behavior.

**Bernoulli's Principle**

The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738. The principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.The aerodynamic lift on the wing of an airplane is also explained in part by this principle.

**Boyles's Law**

**The states that the absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.**

**Charles's Law**

**The law states that when the pressure on a sample of a dry gas is held constant, the Kelvin (absolute) temperature and the volume will be in direct proportion.**

**Coulomb’s Law**

Coulomb's law or Coulomb's inverse-square law, is a law of physics that describes force interacting between static electrically charged particles.

The law states that the magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.

The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different signs, the force between them is attractive.

**Graham’s Law**

Graham's law states that the rate of diffusion or of effusion of a gas is inversely proportional to the square root of its molecular weight. Thus, if the molecular weight of one gas is four times that of another, it would diffuse through a porous plug or escape through a small pinhole in a vessel at half the rate of the other. A complete theoretical explanation of Graham's law was provided years later by the kinetic theory of gases. Graham's law provides a basis for separating isotopes by diffusion.

**Hooke’s Law**

This law states that the extension of a spring is proportional to the tension stretching it. Doubling of the tension results in the doubling of the amount of stretch.

**Kepler's Law**

**Each planet revolves round the Sun in an elliptical orbit with the Sun at one focus. The straight line joining the Sun and the planet sweeps out equal areas in equal intervals. The squares of the orbital periods of planets are proportional to the cubes of their mean distance from the Sun.**

**Law of Conservation of Energy**

The law of conservation of energy states that the total energy of an isolated system remains constant - it is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another. The amount of energy present in the universe is always remain constant.

**Newton’s Laws**

*Law of Gravitation:*

Objects attract each other with a force directly proportional to the product of the masses of the objects and inversely proportional to the square of the distance between them. Hence, for objects on or near the earth, the mass of the earth is very much greater than the object, and so the gravitational force between them makes objects fall towards the earth. That is why lead and feather fall at the same rate in a vacuum.

*Newton’s First law of Motion:*

A body continues in its state of rest, or of uniform motion in a straight line, except in so far as it is compelled by external impressed forces to change that state. It is also called Law of Inertia.

*Newton’s Second Law of Motion:*

The rate of change of momentum is proportional to the impressed force and takes place in the direction of the straight line in which the force acts. In other words “Force is equal to mass multiplied by acceleration”.

*Newton’s Third Law of Motion:*

To every action there is equal and opposite reaction. This is the principle behind the recoil felt on pulling the trigger of a gun.

*Newton’s Law of cooling:*

The rate at which a body cools or loses its heat to its surroundings is proportional to the excess of mean temperature of the body over that of the surroundings, provided this temperature excess is not too large.

**Ohm's Law**

**It states that the current passing through a conductor between two points is directly proportional to the potential difference across the two points provided the physical state and temperature etc. of the conductor does not change.**

**Pascal’s Law**

**When pressure is applied to a fluid, the pressure change is transmitted to every part of the fluid without loss. Hydraulic machines like the hydraulic press work on this principle.**

- Atmospheric pressure decreases with increase in height. The SI unit of pressure is pascal which is named after Pascal who established this law.

**Stefan’s Law**

**The total energy radiated from a black body is equal to the fourth power of its absolute temperature.**

**Tyndall Effect**

The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible. The amount of scattering depends on the frequency of the light and density of the particles.