May the forces be with you!

Surely you are familiar and probably know first-hand the consequences of a fall, either of an object (say phone, glass, keys, etc.), or ourselves; the effect is essentially the same, the objects’ displacement followed by an abrupt and, if we are such object, painful braking; with different results depending on the object.

These events are a corresponding consequence to a fundamental physical force, gravity. Acting as an attraction force between two masses in these cases; in the scenario described, the mass of the earth and the mass of the object. This force literally draws the object to the center of gravity, in this case of the earth. And for this reason we need to apply additional energy to counteract it, such as the effort we make when climbing stairs, or the energy for an airplane to fly, by combining the push impulse from thermal energy generated by the turbines and the aerodynamic lift of the plane. This is also the force that causes the sensation of weight, which is really the earths’ gravity acting on the mass of an object. And in a more colloquial way, it is the force of gravity action that brings us back to the floor, every time we jump.

Well this sounds interesting, but if we talk about “forces” (plural), what are the others?

There are four different fundamental forces acting in the universe, and all matter interactions are related to them. These are the commented force of gravity, the electromagnetic force, the strong nuclear force and the weak nuclear force. So, every interaction and physical effect that we know in any way is related to them.

Electromagnetism

The other force we are more aware of, and interact with at every moment, aside of gravity, is the even more familiar electromagnetic force, also part of our daily life. Sunlight, a lamp’s light, a home television and cellphone screens emit electromagnetic energy in the form of visible light; Yes, visible light is a type of electromagnetic emission. The electromagnetic force, better known as light, has interesting properties such as being formed by the combination of two fields (or effects at a distance), an electric field and a magnetic field, and by having a fixed propagation velocity of 186 thousand miles per second.

Electromagnetic wave

Electromagnetic wave (wikimedia.org)

But its most relevant property is its frequency, the frequency is the periodicity in which a wave is repeated (or the distances between crests), and is measured in cycles per second or “Hertz”. This property is what allows us to have, or rather, distinguish different colors; Of course, based on how our eyes work. Basically, the different colors that we perceive are simply the same manifestation of this force, but with different frequency, going from red, (with lower frequency), to the Violet (of higher frequency). But this force covers much more than just visible light, cases such as wireless communication networks also use this force, but at lower frequencies than visible light, so we cannot perceive them. But if we could, we would see that radio stations’ antennas, the telecommunications towers or even our cell phones would look like bright lamps of microwave light.

The electromagnetic spectrum, or the map of all types of light, varies from the range of ultra-low frequency light, to the mentioned radio waves and microwaves, infrared light, used in remote controls, visible light, ultraviolet light, X-rays, used for medical study purposes, and finally gamma rays, depending on their frequency, the electromagnetic force carries more energy the higher its frequency; For example, infrared light is less energetic than ultraviolet light, and this has less energy that gamma rays. Ultraviolet light for example is the cause for skin burns due prolonged exposure to sunlight without proper protection, but this type of damage is minor if compared to the effects of gamma rays, which are extremely harmful to living beings, as it damages cellular structures.

The electromagnetic force is also considered a long-range force, meaning that the electromagnetic force effect has no distance limit, but is subject to the inverse square’s law, meaning that its strength diminished or becomes more diffuse as we get farther from the source; it is because of this that we can see the light from stars and galaxies that are very far from us, but we receive its light with very little intensity.

Inverse squares law

Inverse squares law (wikipedia.org)

Nuclear forces

Well, now let’s explore a little about the two pending forces; the strong nuclear force is the one that binds protons and neutrons in the atom’s nucleus, this is a force that’s extremely… strong? And unlike the electromagnetic force, it has a very short range, acting in distances of the order of the diameter of the atom’s nucleus, and it’s also the force that keeps the quarks together, quarks are the fundamental particles that form protons and neutrons; this force counteracts the repulsive Coulomb action of protons, given its positive charge (knowing that equal charges repel and opposite charges attract each other).

The weak nuclear force on the other hand controls the decay of sub-atomic particles and determines the radioactivity of certain elements. The called “beta decay”  is the process by which a neutron transforms into a proton, releasing an electron and an “electron-neutrino”, another fundamental particle; that we will see in detail in a future article.

Beta decay

Beta decay (physicslight.wordpress.com)

The biggest distinction between these two nuclear forces is that the strong nuclear force is the basis to form matter by counteracting the charge repulsion and neutron decay. On the other hand, energy generation in stars is based on the fusion of hydrogen atoms, but the process is based on the mentioned beta decay process, in order to form heavier elements, in this case, Helium, releasing large amounts of energy in the process. This force is also involved in nuclear fission, which is the process of division of the nucleus of certain heavy atoms, and the source of radioactivity, this being the method used to generate energy in nuclear plants through the use of uranium.

It is interesting to compare the energy that each of these forces implies, for example, a laser beam, which is electromagnetic energy in the form of coherent and reinforced light of a specific wavelength, can be quite energetic, as in the case of some used in the industry to cut metals; this kind of energy is stronger than that of the nuclear fission processes. But this does not compare to the strong nuclear force that holds together the atom’s nucleus. This force is a hundred times stronger than the electromagnetic force.

Particles

Based on the mentioned standard model of particles, for each of these forces there’s it is considered one associated particle that transmits it. Among the already verified experimentally, is the famous photon, which is the carrier of the electromagnetic force, then we have the gluon, the particle that carries the strong nuclear force, and that holds together the quarks that form neutrons and protons (always in groups of three); and finally, the so-called Bosons W and Z, which are those that transmit the weak nuclear force allowing a quark’s change or transmutation, and in the process causing a neutron to transform into a proton.
In the case of gravity, the graviton has been theorized as the particle that transmits the force of gravity, but this has not been verified experimentally and is one of the great problems of modern physics, given that this force is not associated to the mentioned standard model of particles; a great void certainly. But why this particle can’t be detected? Well, one big factor is since the force of gravity is extremely weak, so much so that we can counteract it on a daily basis in certain actions. For example, when we hold a book or a cup of coffee, we counter the force of gravity that acts on them. Gravity is perceptible only when a large amount of mass accumulates, as in the case of the earth. If we consider for example, the surface of the Moon, clearly less massive than the earth, this force is much lower. The weight of an object on the Moon is only about 16% of what it is on Earth, and that is why the astronauts who visited it could make these great jumps, even with all the gear they carried with them. So, if you need a mass the size of a planet to feel this force’s effect, at atomic level therefore it is very low and extremely difficult to sense and distinguish its fundamental particles.

For example, if we compare the force of gravity with the electromagnetic force, this is forty orders of magnitude weaker. But, what does this mean? Well, if we compare two quantities, say one vs. one million, the latter is six orders of magnitude larger than the number 1, since the number representing one million has six zeros. So, imagine now a quantity with 40, these are too many zeros of difference …, and of those that count, that’s how weak is gravity.

Regards, Alex – ScienceKindle.

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