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The Four Fundamental Forces

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Introduction

Forces are an integral part of understanding how our world works; motion and all phenomena are caused by forces. This is why figuring out the fundamental forces is critical. By doing so, we can study the causes for essentially everything. To our current knowledge, there are only four fundamental forces: gravitational force, electromagnetic force, weak nuclear force, and strong nuclear force. However, the prospect of finding a common root between all of these forces intrigues all sorts of scientists. Someday, physicists hope to be able to categorize all forces as a unified fundamental force.

Gravitational Force

Most people are familiar with the gravitational force. After all, it is the force responsible for the orbit of planets and keeping ourselves on Earth. Sir Isaac Newton first made his observations of gravity in the late 17th century. He figured that the gravitational force was a force between two masses, proportional to the masses involved and inversely proportional to the distance between the masses squared. This equation is known as Newton's Law of Universal Gravitation, which is F=G(m1m2/r2). Despite the advent of new theories of physics such as quantum mechanics, Newton’s models and frameworks prove accurate for most practical uses. Later, in the early 20th century, Albert Einstein would propose that the force of gravity was the curvature of space-time rather than a separation of space and time distinctly. Going back to relativity, it is often shown to students through a demonstration with fabric and spherical objects to show how said objects sink into the fabric, influencing other nearby objects as well. Although there have been centuries of research regarding this fundamental force, there is so much that we still do not know about. In the near future, physicists hope to discover the force-carrier of the gravitational force: the graviton.

Electromagnetic Force

It may seem strange that this is called the electromagnetic force rather than electric and magnetic forces, however, this is because both forces are applied to charged objects. Conventionally, we split the electromagnetic force into an electric force and a magnetic force.  In the late 18th century, Charles-Augustin de Coulomb described the electric force between two stationary charged particles as being proportional to the magnitude of the charge of the two particles and inversely proportional to the distance between them squared. The observation was also made that like charges repel and opposite charges attract. The equation used to describe the electrostatic force is known as Coulomb’s Law, written as F=kq1q2r2. Later in the early 19th century, Michael Faraday would introduce the concept of the electric field, which would allow physicists to consider the electric forces between moving charges. Magnetic fields stem from magnets that have a north and south pole; it is impossible to have one without the other. Like the interactions between singular charges, like poles repel while opposite poles attract. Again, it is important to note that both these forces act as one and are the electromagnetic force. This is shown by the fact that electricity can be used in order to produce a magnetic field and that a changing magnetic flux can be used in order to produce electricity.

Strong interaction

Implied by its name, the strong interaction is the strongest of the four fundamental forces. Within an atom, the three commonly known subatomic particles are the electron, proton, and neutron. Protons and neutrons are located in the center of an atom, forming the nucleus. The strong nuclear force is essential to keep the nucleus of an atom together while also preventing protons and neutrons from breaking apart. Protons and neutrons are composed of quarks, being one of three “colors”: red, blue, and green. In order to form a proton or neutron, a combination of quarks must be combined in order to be “colorless”. This can be done by canceling out “colors” by having a quark of each color. However, quarks also have the ability to constantly change their color by exchanging gluons. Gluons only have color, which means that they change the color of the quark they are leaving and change the color of the quark they are exchanged with. The exchanges between the quarks within protons and neutrons conserve the color cancellation aspect. All of the gluons going back and forth between quarks form a force that keeps the quarks together, known as color force. The color force is essentially a version of strong interaction that is responsible for keeping the protons and neutrons from separating into a bunch of quarks. During the exchanging of gluons, forces outside of the proton or neutron form through pions that are made of two quarks. These two quarks also exchange gluons with each other and to other protons or neutrons, binding them together. This is the nuclear force that keeps the protons and neutrons together in the nucleus.

Weak Interaction

The weak force is responsible for particle decay, an example being radiation. As mentioned while talking about the strong interaction, protons and neutrons are made up of quarks. Electrons are a type of leptons, another subatomic particle. Quarks and leptons have properties known as flavors. The six types of flavors for quarks are known as up, down, top, bottom, strange, and charm while the six types of flavors for leptons are known as the electron, muon, tau, electron-neutrino, muon-neutrino, and tau-neutrino. Protons are composed of two up quarks and one down quark, neutrons are composed of two down quarks and one up quark, and electrons are leptons in and of themselves. The weak interaction changes the flavor of quarks and leptons. The W boson (which can have a positive or negative charge) and Z boson (no charge) are what allow for the changing of flavor. The transferring of bosons can change protons to neutrons and many other combinations of changes. This is known as the weak interaction which allows for all sorts of shifts in atoms by changing the very element that they are.

Conclusion

There is still much that we do not know about the four fundamental forces -- not to mention, it’s possible that there are more fundamental forces that we simply have not discovered yet. In any case, understanding these forces is important as our very reality depends on them. For centuries, we have made major strides in discovering the elementary nature of forces and how they work, and with the advancement of modern physics, many more discoveries will be on their way.

Sources:

Rehm, Jeremy. “The Four Fundamental Forces of Nature.” Space.com, Space, 1 Oct. 2019, …..www.space.com/four-fundamental-forces.html. 

Urone, Paul Peter, and Roger Hinrichs. “23.1 The Four Fundamental Forces - Physics.” OpenStax, …..OpenStax, 26 Mar. 2020, .....openstax.org/books/physics/pages/23-1-the-four-fundamental-forces.

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