The four fundemental forces of nature

There are four fundamental forces: Electromagnetism, gravity, the strong force, and the weak force. The strong force is the force that keeps the parts of an atom together. It makes quarks stick to each other, and it makes protons and neutrons cluster. The weak force causes atomic decay, which makes certain elements radioactive. Examples of these elements are Uranium, Plutonium, and Cobalt. The electromagnetic force has its own particle, called the photon. Light is classified under the field of electromagnetism. Finally, there is gravity. Gravity is the tendency of objects with mass to attract each other with a specific force. We know a lot about these forces, but until 20 years ago, we didn't know very much about why they existed.