The four fundamental forces of nature are really the four ways matter interacts in the universe. Gravity, the weakest of the four, is present in people's everyday lives, but paradoxically seems quite strong. The electromagnetic force runs our electric machines, the Internet and smart phones. The other two forces, the strong and the weak nuclear forces, operate on the atomic level and influence elementary particles such as protons and electrons. These four forces are the reason the world exists as it does, with each force having unique properties and characteristics.
TL;DR (Too Long; Didn't Read)
The four fundamental forces of nature, strongest to weakest, are the strong nuclear force, the electromagnetic force, the weak nuclear force and gravity.
Fundamental Force Basics
When inanimate objects or elementary particles interact, the fundamental forces influence their behavior. For example, planets orbit around the sun because of the gravitational force. Lightning strikes because electrons jump between clouds and the ground due to the electromagnetic force. Atoms stay together because of the strong nuclear force, and natural radiation is caused by the weak nuclear force.
These forces have two main characteristics in common. They have strength and they act over a certain distance. Beyond that, they are each unique and act on matter in completely different ways.
The Strong Nuclear Force
The most powerful of the four forces is the strong nuclear force, which has to overcome the number two force, electromagnetism, in the atomic nucleus. Nuclei are made up of protons and neutrons, with the protons repelling each other due to their positive charges. The strong nuclear force overcomes this repulsion and holds the protons close together in the nucleus.
To be able to compare the strength of the fundamental forces, scientists often use the strong nuclear force as the basis and assign it a value of 1. The strength of each of the other forces, which are weaker, is given as a fraction of this strength. While it is the most powerful force, the strong nuclear force does not act at a distance. It is confined to the nucleus of an atom and only has a range of approximately the radius of an average nucleus.
The Electromagnetic Force
The electromagnetic force acts on charged particles and is the key interaction in anything to do with electricity. Because most matter has a balance of charged particles, large objects tend to be neutral and the force has no effect on them. When objects become charged, such as in electric motors, in batteries or with static electricity, like charges repel and unlike charges attract. Electrons are the negative-charge carriers and are attracted to protons, which have a positive charge. When charges move, they create magnetic fields that have north and south poles. As with charges, two like poles repel and different poles attract.
The electromagnetic force is just under one hundredth the strength of the strong nuclear force, but it can act at a distance. While it gets weaker when the charged objects are further apart, the attraction and repulsion theoretically continue to infinity. However, at great distances the effects are tiny and can be negligible.
The Weak Nuclear Force
While the strong nuclear force acts only on particles in the nucleus, the weak nuclear force acts on many elementary particles and is responsible for natural radiation. It governs the way elements break down naturally over time, and when the atoms are no longer held together, particles such as electrons are expelled in the form of radiation. As a result, the weak nuclear force influences how nuclear fission and nuclear fusion take place.
The weak force is less than one millionth as strong as the strong nuclear force, and it acts at only very short distances. While it can attract and repel particles, its operating range is so limited that it doesn't really act like the other forces, which pull or push over a distance. The weak nuclear force is more like a glue or grease, active only in a thin layer between elementary particles.
The Gravitational Force
Gravity acts as an attractive force between any two objects that have mass. The force of gravity depends on the mass of the objects. In everyday life, the force of gravity between the earth and objects such as a car is the weight of the car. The force of gravity is directly proportional to the mass of the objects. For example, 2 quarts of milk weigh twice as much as 1 quart.
Gravity is the weakest force and is less than one millionth of a millionth the strength of the strong nuclear force. Although very weak on an atomic level, everyday objects have so much mass that the force of gravity becomes quite strong. For even more mass, such as in planets and stars, the force of gravity is strong enough to keep them in orbit. Gravity is like the electromagnetic force in that it acts at a distance, theoretically out to infinity. This becomes important for huge masses such as galaxies that attract other galaxies even when they are very far apart.
It is easy to imagine other forces active in nature, such as the wind, an explosion or the force of a jet engine. These are all secondary forces that rely on the fundamental forces for their action. For example, the wind blows because weather involves hot air rising and cold air falling, the cold air being heavier due to gravity. The wind has force because the molecules of the air are held together by the fundamental forces, allowing them to exert a push. In fact, the four fundamental forces are behind everything living being experiences.