The physical sciences are those sciences that are concerned with the physical world. It is one of the two main divisions of science, the other being the life sciences. These are sciences that are concerned with living organisms. Physical sciences covers everything form sub-atomic particles to the workings of the universe.
Physics is perhaps the most fundamental of all the physical sciences. While other physical sciences describe aspects of the physical universe, like chemical reactions or the stars, physics describes the whole universe, including the very space and time such things as chemicals and stars exist in. Topics in physics include the laws of motion, such as those that describe projectiles and falling objects. They include the theory of relativity. They also include the laws that govern the fundamental forces, such as electricity, magnetism and gravity. They describe phenomena such as heat, light and energy, as well as principles on which all machines work. Other major areas of physics involve the study of subatomic matter, such as nuclear science and quantum mechanics.
Chemistry is the study of chemical reactions. It includes the study of creating compounds of chemicals that have particular properties and also the breaking down of compounds to find out what substances they are made out of. It describes the laws that govern how atoms join together to form molecules. It includes organic chemistry, or the study of the chemical processes found in living organisms.
Astronomy is the study of the other planets, the stars, galaxies and the whole universe outside Earth. It involves the mapping of the night sky, and this often involves the use of high-tech telescopes. Astronomy includes the study of cosmology, or the formation and nature of the universe. It describes the laws that caused Earth to form. It involves the study of pulsars, nebulae, black holes and other obscure cosmic phenomena.
Earth science is a broad category that includes such disciplines as geology, meteorology and oceanography. It is the study of planet Earth as a whole and of the factors that go into making it the way that it is. It draws from other sciences such as physics and chemistry. It includes the study of the chemical and physical processes of the planet and the elements that make it up. It involves the study of how life alters the planet.