Introduction to the Major Laws of Physics

Portrait of Isaac Newton (1642-1727), c.1726 (oil on canvas)
Enoch Seeman / Getty Images

Over the years, one thing scientists have discovered is that nature is generally more complex than we give it credit for. The laws of physics are considered fundamental, although many of them refer to idealized or theoretical systems that are hard to replicate in the real world.

Like other fields of science, new laws of physics build on or modify existing laws and theoretical research. Albert Einstein's theory of relativity, which he developed in the early 1900s, builds on the theories first developed more than 200 years earlier by Sir Isaac Newton.

Law of Universal Gravitation

Sir Isaac Newton's groundbreaking work in physics was first published in 1687 in his book "The Mathematical Principles of Natural Philosophy," commonly known as the Principia. In it, he outlined theories about gravity and of motion. His physical law of gravity states that an object attracts another object in direct proportion to their combined mass and inversely related to the square of the distance between them.

Three Laws of Motion

Newton's three laws of motion, also found in the Principia, govern how the motion of physical objects change. They define the fundamental relationship between the acceleration of an object and the forces acting upon it.

  • First rule: An object will remain at rest or in a uniform state of motion unless that state is changed by an external force. 
  • Second rule: Force is equal to the change in momentum (mass times velocity) over time. In other words, the rate of change is directly proportional to the amount of force applied. 
  • Third rule: For every action in nature there is an equal and opposite reaction. 

Together, these three principles that Newton outlined form the basis of classical mechanics, which describes how bodies behave physically under the influence of outside forces.

Conservation of Mass and Energy

Albert Einstein introduced his famous equation E = mc2 in 1905 journal submission titled, "On the Electrodynamics of Moving Bodies." The paper presented his theory of special relativity, based on two postulates:

  • Principle of relativity: The laws of physics are the same for all inertial reference frames. 
  • Principle of constancy of the speed of light: Light always propagates through a vacuum at a definite velocity, which is independent of the state of motion of the emitting body.

The first principle simply says that the laws of physics apply equally to everyone in all situations. The second principle is the more important one. It stipulates that the speed of light in a vacuum is constant. Unlike all other forms of motion, it is not measured differently for observers in different inertial frames of reference.

Laws of Thermodynamics

The laws of thermodynamics are actually specific manifestations of the law of conservation of mass-energy as it relates to thermodynamic processes. The field was first explored in the 1650s by Otto von Guericke in Germany and Robert Boyle and Robert Hooke in Britain. All three scientists used vacuum pumps, which von Guericke pioneered, to study the principles of pressure, temperature, and volume.

  • 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 that is perfectly efficient.

Electrostatic Laws

Two laws of physics govern the relationship between electrically charged particles and their ability to create electrostatic force and electrostatic fields. 

  • Coulomb's law is named for Charles-Augustin Coulomb, a French researcher working in the 1700s. The force between two point charges is directly proportional to the magnitude of each charge and inversely proportional to the square of the distance between their centers. If the objects have the same charge, positive or negative, they will repel each other. If they have opposite charges, they will attract each other.
  • Gauss's law is named for Carl Friedrich Gauss, a German mathematician who worked in the early 19th century. This law states that net flow of an electric field through a closed surface is proportional to the enclosed electric charge. Gauss proposed similar laws relating to magnetism and electromagnetism as a whole.

Beyond Basic Physics

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.