Connection for ap® courses

Continuing to use ideas that would be familiar to the ancient Greeks, we look for smaller and smaller structures in nature, hoping ultimately to find and understand the most fundamental building blocks. Atomic physics deals with the smallest units of elements and compounds. Through the study of atomic physics, we have found a relatively small number of atoms with systematic properties that explain a tremendous range of phenomena.

Nuclear physics is concerned with the nuclei of atoms and their substructures, supporting Big Idea 1, that systems have internal structure. Furthermore, the internal structure of a system determines many properties of the system (Enduring Understanding 1.A). Here, a smaller number of components—the proton and neutron—make up all nuclei. Neutrons and protons are composed of quarks. Electrons, neutrinos, photons, and quarks are examples of fundamental particles. The positive electric charge on protons and neutral charge on neutrons result from their quark compositions (Essential Knowledge 1.A.2).

This chapter divides elementary particles into fundamental particles as objects that do not have internal structure and composed particles whose properties are defined by their substructures (Essential Knowledge 1.A.2). The magnetic dipole moment, related to the properties of spin (angular momentum) and charge, is an intrinsic property of some fundamental particles such as the electron (Essential Knowledge 1.E.6). This property is the fundamental source of magnetic behavior in matter (Enduring Understanding 1.E).

Exploring the systematic behavior of interactions among particles has revealed even more about matter, forces, and energy. Mass and electric charge are properties of matter that are conserved (Enduring Understanding 1.C). The total energy of the system is also conserved (Enduring Understanding 5.B). In quantum mechanical systems, mass is actually part of the internal energy of an object or system (Essential Knowledge 5.B.11). It has been discovered experimentally that, due to certain interactions between systems, mass can be converted to energy and energy can be converted to mass (Essential Knowledge 1.C.4, Essential Knowledge 4.C.4), supporting Big Idea 4. These process can also lead to changes in the total energy of the system (Enduring Understanding 4.C).

Particle physics deals with the substructures of atoms and nuclei and is particularly aimed at finding those truly fundamental particles that have no further substructure. In general, any system can be viewed as a collection of objects, where objects do not have internal structure (Essential Knowledge 1.A.1). Just as in atomic and nuclear physics, we have found a complex array of particles and properties with systematic characteristics analogous to the periodic table and the chart of nuclides. We have discovered that changes in the systems are constrained by the conservation laws, supporting Big Idea 5. In the case of elementary particles, these conservation laws include mass-energy conservation and conservation of electric charge (Enduring Understanding 5.C). Electric charge is conserved in elementary particle reactions, even when elementary particles are produced or destroyed (Essential Knowledge 5.C.1).