Nuclei are the central cores of atoms, composed of protons and neutrons, collectively known as nucleons. They are held together by the strong nuclear force, one of the four fundamental forces of nature. The number of protons in a nucleus determines the element, while the number of neutrons can vary, leading to different isotopes of the same element.
Understanding nuclei is crucial for various fields, including nuclear energy, medicine (such as in radiotherapy), and astrophysics. The study of nuclei helps scientists explore the fundamental properties of matter and the forces that govern the universe.