Gravity is an attractive force between any two objects with mass and is the weakest of the four fundamental forces. Electromagnetism acts on all particles possessing electric charge, mediating interactions like light and magnetism. The weak nuclear force is responsible for certain types of radioactive decay, such as beta decay, where a neutron transforms into a proton. The strong nuclear force, the strongest of the four, binds quarks together to form protons and neutrons, and also holds protons and neutrons together within the atomic nucleus.