The energy required to do this comes from not only the arms, but the legs as well. The study of light is called optics. It involves learning what light is, how it behaves, and how it can be used. A knowledge of how light behaves has helped in the development of instruments such as the microscope and the telescope. Doctors are now able to use lasers for surgery.
Lasers are devices for the creation and amplification of a narrow, intense beam of coherent light.
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.