Physics is one of the physical sciences. This means that it studies the laws that govern the physical world. (The life sciences, on the other hand, study living organisms).

Physics tries to understand the nature of basic things such as motion, forces, energy, matter, heat, sound, and light. Because these are found throughout the universe, physicists study a wide range of things. Black holes, atoms, engines, elevators, and baseballs all obey the laws of physics. You might find a physicist smashing atomic particles together to find out how the universe began, or you might find a physicist orbiting the earth as an astronaut. Physicists also work in hospitals designing new instruments or scanning techniques. Some physicists create smaller, faster electronics for the next generation of computers.

Physics is relevant to many other sciences, such as astronomy, biology, and geology. The combinations of these fields are called astrophysics, biophysics, and geophysics. Engineers apply physics to design things; in fact, some students study a subject called Engineering Physics.

Physics often uses mathematics to describe the laws of nature. One of the most famous equations of this type was Einstein's formula E=mc², where E is energy, m is mass, and c is the speed of light. This formula, put simply, says that matter can be transformed into energy, and energy can be transformed into matter. Physics doesn't have to use mathematics to express the laws of the physical world. Some principles are better expressed in words, like the important Law of Conservation of Energy, which states that energy cannot be created or destroyed.

When we talk about "laws" of physics, we are not being totally accurate. A better word might be "theories". This is because they are always being updated as physicists learn more about the physical world. Physics is a very old science, and some of the "laws" of physics from ancient times are no longer believed today. For example, the ancient Greek physicist Aristotle believed that things fell towards the earth because it was "natural" for them to be there. Now we believe that things fall to the earth because they are affected by the force of gravity. Perhaps in the future we will have a new theory to explain this phenomenon.