Physics experiments are used to observe physical phenomena in controlled situations in order to discern information about the workings of the universe. Some physics experiments have been conducted many times and are used for educational purposes, while some are being conducted for the first time and seek to discover more information about the nature of the universe. Much of modern physics is concerned only with unverifiable mathematical equations, but the field of experimental physics is integral to the broad field of physics.
Physics students from early high school through all stages of their educations regularly conduct physics experiments. In high school, the experiments usually serve to demonstrate and prove simple physical principles to the students. They are generally concerned with general topics such as gravity or rotational motion. Other commonly addressed topics are electricity and fluid motion.
In college, most classroom physics courses are coupled with physics labs. In such lab courses, students conduct a wide array of physics experiments that correspond to the topics learned in the classroom. Generally speaking, these topics are more advanced than those taught in high school courses. The experiments are correspondingly more rigorous and more advanced. They cover topics similar to those taught in high school, but they have much more depth.
Physicists have been theorizing and working to make a mathematical model of the universe for a very long time. The proposed mathematical explanations for physical phenomena tend to be decades ahead of scientists' abilities to experimentally verify them. For example, Einstein developed his theories of special relativity and general relativity in 1906 and 1916, respectively. While parts of these theories have been experimentally verified, there are still aspects of them that exist only in the form of mathematical equations.
It is becoming increasingly costly to conduct effective physics experiments as the subjects of study tend to be either incredibly small or incredibly massive. For example, the Large Hadron Collider was constructed to prove the existence of the Higgs-Boson particle by colliding other incredibly small particles and examining the results of the collision. The cost of the collider, before even considering the massive amount of energy required to run it, is in the billions of US dollars.
The Large Hadron Collider, despite its cost, is an excellent example of what exactly a physics experiment is. Its purpose is to collide particles and observe what results from the collision. It does so under very controlled conditions—the entire apparatus is maintained at a specific temperature and the particles are accelerated to very specific speeds. As in other science experiments, the Large Hadron Collider allows scientists to observe a natural phenomenon under controlled circumstances. They can draw their own conclusions from what they observe.