A force is an energetic influence that can cause an object to change its velocity. A force has magnitude and direction. The unit of force is the newton (N).
Isaac Newton described the three laws of motion of all objects using inertia and force.
- The first law of motion states that an object will remain at rest or in uniform motion unless acted upon by an external force.
- The second law of motion states that the force acting on an object is equal to its mass times its acceleration. F=ma.
- The third law of motion states that whenever one body exerts a force on another, it exerts an equal and opposite force on the first.
There are five fundamental forces:[]
| Electromagnetic | The force of attraction that binds negatively-charged electrons to the positively-charged protons in the nucleus, critical to the structure of the atom. It is responsible for electricity and magnetism, and is the force carrier for photons in the electromagnetic spectrum. |
| Gravitational | The force that attracts objects with mass toward each other. It’s what keeps us on the ground, makes things fall, and causes the planets to orbit the sun. Gravity acts over long distances, but it is the weakest of the fundamental forces. |
| Weak interaction | The force responsible for processes like radioactive decay, where particles like neutrons change into protons, or vice versa. Unlike the strong force, which holds atomic nuclei together, the weak force acts over a very short distance and is much weaker, but it plays a key role in the behavior of subatomic particles. |
| Strong interaction | The force that holds the nucleus of an atom together. It is the strongest of the four fundamental forces and acts between protons and neutrons, as well as quarks inside these particles. The strong force works over very short distances, keeping the particles tightly bound within the nucleus. |
| Quintessence | The force of dark energy, regulating the expansion of the universe. |
The strong force is approximately 137 times as strong as electromagnetism, 106 times as strong as the weak force, and 1038 times as strong as gravitation.
During the Big Bang's Planck Epoch (at around 10−43 seconds), the four fundamental forces of nature (gravity, electromagnetism, the strong nuclear force, and the weak nuclear force) formed a single superforce. The Inflationary Epoch gave rise to quintessence, and the superforce split into the four fundamental forces. Eventually the discovery of the Theory of Everything would once again unify quantum mechanics and general relativity and all forces back into the superforce.