The study of sound is called acoustics. Ultrasound is used in the medical field for destroying various unwanted substances in the body such as kidney stones. Ultrasound uses sound waves to dissolve these foreign bodies. If not for physics, ultrasounds would never have been discovered and utilized. Electricity and magnetism are closely related.
Electricity can produce magnetism, and magnetism can produce electricity.
An understanding of this important relationship has led to the development of many valuable inventions. In the field of medicine, MRI scans, are another new discovery based on the principle of electromagnetism and the phenomenon that nuclei of some atoms line up in the presence of an electromagnetic field. They are able to show a complete three dimensional picture of the interior structure of the body, and are extremely valuable in hospitals. The study of heat is called thermodynamics. Physicist study how heat can be changed into work, how it is produced, how it is transferred from one place to another, and how it changes matter.