Four Fundamental Forces
Gravitational Force: Is a pull between any two objects that was directly related to their masses and inversely related to the distance in between them. Anything that has a mass has gravity. This is considered the weakest of the four forces but works at a practically infinite range.
Weak Force: Responsible for radioactive decay, which plays an essential role in nuclear fission. Considered to be the 3rd strongest force of the Four Forces.
Strong Force: This is the Force that holds the nucleus of the atom together. Strong Force is the strongest of the Four Fundamental Forces but it only works over a short distance
Electromagnetism: The force that pulls atoms together. Atoms are a lot like magnets. Magnets with opposite charges attract, and like charges repel. This is the 2nd strongest force following Strong Force.
Einstein’s Theory of General Relativity
The theory of general relativity describes the force of gravity. General relativity was developed by Einstein in the early 1900´s. General relativity is a geometrical theory which explains that the presence of matter curves spacetime, and this curvature affects the path of particles. It uses the mathematics to describe gravity without the use of the force of gravity. This theory considers everything to be equal, not only those moving with uniform speed.