Physics - major concepts

Fields of Physics

Major Laws of Physics

Fundamental Forces of Physics

What are the Fields of Physics?

Answer:

Physics is a diverse area of study and in order to make sense of it scientists have been forced to focus their attention on one or two smaller areas of the discipline. This allows them to become experts in that narrow field, without getting bogged down in the sheer volume of knowledge that exists regarding the natural world.

Below is a list - by no comprehensive - of different disciplines of physics. The list will be updated with new additions and definitions as appropriate.

• Acoustics - the study of sound & sound waves
• Astronomy - the study of space
• Astrophysics - the study of the physical properties of objects in space
• Atomic Physics - the study of atoms, specifically the electron properties of the atom
• Biophysics - the study of physics in living systems
• Chaos - the study of systems with strong sensitivity to initial conditions, so a slight change at the beginning quickly become major changes in the system
• Chemical Physics - the study of physics in chemical systems
• Computational Physics - the application of numerical methods to solve physical problems for which a quantitative theory already exists
• Cosmology - the study of the universe as a whole, including its origins and evolution
• Cryophysics / Cryogenics / Low Temperature Physics - the study of physical properties in low temperature situations, far below the freezing point of water
• Crystallography - the study of crystals and crystalline structures
• Electromagnetism - the study of electrical and magnetic fields, which are two aspects of the same phenomenon
• Electronics - the study of the flow of electrons, generally in a circuit
• Fluid Dynamics / Fluid Mechanics - the study of the physical properties of "fluids," specifically defined in this case to be liquids and gases
• Geophysics - the study of the physical properties of the Earth
• High Energy Physics - the study of physics in extremely high energy systems, generally within particle physics
• High Pressure Physics - the study of physics in extremely high pressure systems, generally related to fluid dynamics
• Laser Physics - the study of the physical properties of lasers
• Mathematical Physics - applying mathematically rigorous methods to solving problems within physics
• Mechanics - the study of the motion of bodies in a frame of reference
• Meteorology / Weather Physics - the physics of the weather
• Molecular Physics - the study of physical properties of molecules
• Nanotechnology - the science of building circuits and machines from single molecules and atoms
• Nuclear Physics - the study of the physical properties of the atomic nucleus
• Optics / Light Physics - the study of the physical properties of light
• Particle Physics - the study of fundamental particles and the forces of their interaction
• Plasma Physics - the study of matter in the plasma phase
• Quantum Electrodynamics - the study of how electrons and photons interact at the quantum mechanical level
• Quantum Mechanics / Quantum Physics - the study of science where the smallest discrete values, or quanta, of matter and energy become relevant
• Quantum Optics - the application of quantum physics to light
• Quantum Field Theory - the application of quantum physics to fields, including the fundamental forces of the universe
• Quantum Gravity - the application of quantum physics to gravity and unification of gravity with the other fundamental particle interactions
• Relativity - the study of systems displaying the properties of Einstein's theory of relativity, which generally involves moving at speeds very close to the speed of light
• Statistical Mechanics - the study of large systems by statistically expanding the knowledge of smaller systems
• String Theory / Superstring Theory - the study of the theory that all fundamental particles are vibrations of one-dimensional strings of energy, in a higher-dimensional universe
• Thermodynamics - the physics of heat

It should become obvious that there is some overlap. For example, the difference between astronomy, astrophysics, and cosmology can be virtually meaningless at times ... to everyone, that is, except the astronomers, astrophysicists, and cosmologists, who can take the distinctions very seriously.

Major Laws of Physics

About Physical Laws:

Over the years, one thing scientists have discovered is that nature is generally more complex than we give it credit for. The following laws of physics are considered fundamental, but many of them refer to idealized, closed systems, which are hard to obtain in the real world. Also, some are altered slightly in different circumstances. Newton's laws of motion, for example, are modified by the findings of the theory of relativity, but they are still basically valid.

Newton's Three Laws of Motion:

Sir Isaac Newton developed the Three Laws of Motion, which define the fundamental relationship between the net acceleration of an object and the net forces acting upon it.

"Law" of Gravity:

Newton developed his "Law of Gravity" to explain the attractive force between a pair of masses. In recent years, it has become 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.

Conservation of Mass-Energy:

The total energy in a closed or isolated system is constant, no matter what happens. Another law stated that the mass in an isolated 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, which says the total of both is retained, although some may change forms. The ultimate example of this is a nuclear explosion, where mass transforms into energy.

Conservation of Momentum:

The total momentum in a closed or isolated system remains constant. An alternative of this is the law of angular momentum.

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 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.

Electrostatic Laws:

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.

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.

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.

What are the Fundamental Forces of Physics?

Question: What are the Fundamental Forces of Physics?
Sometimes there are references to the "four fundamental forces of physics." What are the fundamental forces? Why are they fundamental?

Answer: The fundamental forces (or fundamental interactions) of physics are the ways that individual particles interact with each other. It turns out that for every single interaction that we've observed take place in the universe, they can be broken down to be described by only four (well, generally four - more on that later) types of interactions:

• Gravity
• Electromagnetism
• Weak Interaction (or Weak Nuclear Force)
• Strong Interaction (or Strong Nuclear Force)

Gravity

Of these forces, gravity has the furthest reach but it's the weakest in actual magnitude.

It is a purely attractive force which reaches through even the "empty" void of space to draw two masses toward each other. It keeps the planets in orbit around the sun and the moon in orbit around the Earth.

Gravitation is described under the theory of general relativity, which defines it as the curvature of spacetime around an object of mass. This curvature, in turn, creates a situation where the path of least energy is toward the other object of mass.

Electromagnetism

Electromagnetism is the interaction of particles with an electrical charge. Charged particles at rest interact through electrostatic forces, while in motion they interact through both electrical and magnetic forces.

For a long time, the electric and magnetic forces were considered to be different forces, but they were finally unified by James Clerk Maxwell in 1864, under Maxwell's equations. In the 1940s, quantum electrodynamics consolidated electromagnetism with quantum physics.

Electromagnetism is perhaps the most obviously prevalent force in our world, as it can affect things at a reasonable distance and with a fair amount of force.

Weak Interaction

The weak interaction is a very powerful force that acts on the scale of the atomic nucleus. It causes phenomena such as beta decay. It has been consolidated with electromagnetism as a single interaction called the "electroweak interaction."

Strong Interaction

The strongest of the forces is the aptly-named strong interaction, which is the force that, among other things, keeps nucleons (protons & neutrons) bound together. In the helium atom, for example, it is strong enough to bind two protons together despite the fact that their positive electrical charges cause them to repulse each other.

In essence, the strong interaction allows particles called gluons to bind together quarks to create the nucleons in the first place. Gluons can also interact with other gluons, which gives the strong interaction a theoretically infinite distance, although it's major manifestations are all at the subatomic level.

Unifying the Fundamental Forces

Many physicists believe that all four of the fundamental forces are, in fact, the manifestations of a single underlying (or unified) force which has yet to be discovered. Just as electricity, magnetism, and the weak force were unified into the electroweak interaction, they work to unify all of the fundamental forces.

The current quantum mechanical interpretation of these forces is that the particles do not interact directly, but rather manifest virtual particles that mediate the actual interactions. All of the forces except for gravity have been consolidated into this "Standard Model" of interaction.

The effort to unify gravity with the other three fundamental forces is called quantum gravity. It postulates the existence of a virtual particle called the graviton, which would be the mediating element in gravity interactions. To date, gravitons have not been detected and no theories of quantum gravity have been successful or universally adopted.