Major Laws of Physics

Physics is the study of nature, where it is a field of science that that treats the laws and properties of matter and the forces acting upon them (light, magnetism, heat and gravitation, to name a few).  To be put simply, physics is the study to find out how the universe behaves.  Physics is one of the oldest academic disciplines, perhaps the oldest after the inclusion of Astronomy.  It has been the catalyst to many modern innovations in mechanical engineering, quantum physics, chemical physics, thermodynamics and industrialisation.  

Throughout the years, physicists start to see that nature is more complex than we give it credit for.  The following laws of physics are considered fundamental in the study of physics but there has been alterations throughout the years by physicists in the objective of trying to be less idealistic and less rigid.  However, in many instances, physics still remains a very closed system with idealistic concepts, which are hard to find in the real world.  Nevertheless, the following laws of physics are fundamental and in many ways, valid in most cases that you'll run into.

Law 1:  Newton's Three Laws of Motion

Newton's Three Laws of Motion describes the basic rules of how the motion of objects change.  He was able to explain the fundamental relationship between the acceleration of an object and the total forces acting upon it.  

Law 2:  Law of Gravity

Newton developed his "Law of Gravity" to explain the attractive force between a pair of masses. In the twentieth century, it became clear that this is not the whole story, as Einstein's theory of general relativity has provided a more comprehensive explanation for the phenomenon of gravity. Still, Newton's law of gravity is an accurate low-energy approximation that works for most of the cases that you'll explore in physics.

Law 3:  Conservation of Mass Energy

The basic principle of this law is that the total energy in a closed system is constant, no matter what happens.   Another law is that the total mass in a closed system is constant.  When Einstein discovered the relationship E=mc² (in other words that mass was a manifestation of energy) the law was said to refer to the conservation of mass-energy. The total of both mass and energy is retained, although some may change forms. The ultimate example of this is a nuclear explosion, where mass transforms into energy.

Law 4:  Conservation of Momentum

A principle stating that the total linear momentum of an isolated system remains constant regardless of changes within the system.

Law 5:  Law of Thermodynamics

Thermodynamics is the study of the inter-relation between heat, work and internal energy of a system. 

• The zeroeth law of thermodynamics makes the notion of temperature possible.
• The first law of thermodynamics demonstrates the relationship between internal energy, added heat, and work within a system.
• The second law of thermodynamics relates to the natural flow of heat within a closed system.
• The third law of thermodynamics states that it is impossible to create a thermodynamic process which is perfectly efficient.

The British scientist and author C.P. Snow had an excellent way of remembering the three laws:

1. You cannot win (that is, you cannot get something for nothing, because matter and energy are conserved).
2. You cannot break even (you cannot return to the same energy state, because there is always an increase in disorder; entropy always increases).
3. You cannot get out of the game (because absolute zero is unattainable).

Law 6:  Electrostatic Law

Coulomb's law and Gauss's law are formulations of the relationship between electrically charged particles to create electrostatic force and electrostatic fields. The formulas, it turns out, parallel the laws of universal gravitation in structure. There also exist similar laws relating to magnetism and electromagnetism as a whole.

Law 7:  Invariance of the Speed of Light:

Einstein's major insight, which led him to the Theory of Relativity, was the realization that the speed of light in a vacuum is constant and is not measured differently for observers in different inertial frames of reference, unlike all other forms of motion. Some theoretical physicists have conjectured different variable speed of light (VSL) possibilities, but these are highly speculative. Most physicists believe that Einstein was right and the speed of light is constant.

Law 8:  Modern Physics & Physical Laws:

In the realm of relativity and quantum mechanics, scientists have found that these laws still apply, although their interpretation requires some refinement to be applied, resulting in fields such as quantum electronics and quantum gravity. Care should be taken in applying them in these situations.

Some parts taken from:  http://physics.about.com/od/physics101thebasics/p/PhysicsLaws.htm