There are many different types of physical forces in our daily life, for example, the elastic force between two objects linked by an elastic band, the gravitational force between the Earth and the Moon, the electric force between the electrons in a wire, etc. Physicists have found that, out of these many different types of forces, only 4 of them are fundamental. These are the gravity, electromagnetic force (electric and magnetic forces are in fact the same), strong and weak nuclear forces. All the other forces can be treated as the result of these 4 forces.

You will probably be familiar with gravity and the electromagnetic force, but how about the strong and weak nuclear forces? The strong nuclear force accounts for the binding between the nucleus in an atom, that is, the protons and neutrons are stuck together in an atom by the strong nuclear force while the weak nuclear force accounts for a nuclear decay called the b decay.

Basically, the strong force is much, much stronger than the weak force. Normally, the strong force is stronger than the weak force and the weak force is stronger than the electromagnetic force, while the gravity is the weakest. Although it may sounds strange that the gravity is the weakest force, because in our daily life, the gravity that we experienced is much stronger than the electromagnetic force we experienced. However, that is because the gravitational force is always attractive while the electromagnetic force's repulsive part has been cancelled with its attractive part and result in a zero net force.