Applied physics is a area that focuses on using the principles of physics to solve real-world problems. While applied physics and engineering are sometimes used interchangeably, they are in fact different to how they approach problems. While engineering seeks to apply established physics problems, applied physics is more closely related to research, hypotheses, and experimentation. Applied physics tries to develop new understandings by attempting to solve problems that have proven challenging or elusive to fully solve or conceptualize. Many may argue that applied physics is actually an amalgamation of both, physics and engineering.
For instance, while engineering would be necessary to put together an airliner by applying knowledge already developed, applied physics actively engages to push the boundaries of current understandings by trying to research, for example, how to make an airliner safer or more resistant to turbulence.
Given the foundational principles of attempting to solve problems and develop new understandings, scientists who work within the field of applied physics usually conduct interdisciplinary studies and research, covering areas such biology, chemistry, and engineering.