Applied physics

Summary

Applied physics is the study and application of the behavior of condensed matter. These include solids, liquids, and gases, in bulk quantities. Applied physics is the basis of all engineering and design that requires the interaction of individual components and materials. The study of applied physics now extends into numerous other fields, including physics, chemistry, biology, engineering, medicine, geology, meteorology, and oceanography.

Definition and Basic Principles

Applied physics is the study of the behavior and interaction of condensed matter. Condensed matter is commonly recognized as matter in the phase forms of solids, liquids, and gases. Each phase has its own unique physical characteristics. Also, each material has its own unique physical suite of properties that derive from its chemical identity. The combination of these traits determines how something consisting of condensed matter interacts with something else that consists of condensed matter.

The interactions of constructs of condensed matter are governed by the interaction of forces and other vector properties that are applied through each construct. A lever, for example, functions as the medium to transmit a force applied in one direction so that it operates in the opposite direction at another location. Material properties and strengths are also an intimate part of the interaction of condensed matter. A lever that cannot withstand the force applied to it laterally will bend or break rather than function as a lever. Similarly, two equally hard objects, such as a train car's wheels and the steel tracks that they roll, rebound elastically with little or no generation of friction. If one of the materials is not as hard as the other, as in the case of a steel rotor and a composition brake pad, friction characterizes their interaction.

Background and History

Applied physics is the oldest of all practical sciences, dating back to the first artificial use of an object by pre-historic humans. These basic practices have been used by builders and designers for thousands of years. With the development of mathematics and measurement, applied physics has grown. This is because it relies on the application of basic concepts of vector properties (force, momentum, velocity, weight, moment of inertia) and the principles of simple machines (lever, ramp, pulley).

The modern concept of applied physics can be traced back to the Greek philosopher Aristotle c. 350 Before the Common Era (BCE), who identified several separate fields for systematic study. The basic mathematics of physics was formulated by Pythagoras about two hundred years before. These were certainly known to the Babylonians as early as 1600 BCE. Perhaps the greatest single impetus for the advance of applied physics was the development of calculus by Sir Isaac Newton and the fundamental principles of Newtonian mechanics in the seventeenth century. Those principles accurately describe the behaviors of objects composed of condensed matter. They do falter, however, as the scale involved becomes very small, such as below the scale of nanotechnology. As the Industrial Revolution carried into the twenty-first century, the advancing capabilities of technology and materials combined to enable even more advances and applications. Nonetheless, all continued to follow the same basic rules of physics as the crudest of constructs.

How It Works

As the name implies, applied physics means the application of the principles of physics to material objects. The most basic principles of applied physics are those that describe and quantify matter in motion. These are speed, velocity, acceleration, momentum, inertia, mass, and force. These principles lead to the design and implementation of devices and structures. Their basic purpose is physical function or action, either individually or in concert.

A second and equally important aspect of applied physics is the knowledge of the physical properties and characteristics of the materials being used. This includes physical properties such as melting and boiling points, malleability, thermal conductivity, and electrical resistivity. Others are magnetic susceptibility, density, hardness, sheer strength, tensile strength, compressibility, granularity, and absorptivity. These physical factors determine the suitability of materials for given tasks. Understanding these factors also enables the identification of new applications for those materials.

Design. Applied physics is the essential basis for the design of artificial objects. They range from the tiniest of nanoprobes and the simplest of levers to the largest and most complex of machines and devices. The process starts with a need. This is typically a task that is needed to be performed. This is matched with a potential device that can perform the task. The design process moves to an assessment of the physical environment in which the device must function against the forces that will be exerted against it. Also, consideration is given to the forces required to accomplish the task. The appropriate materials may then be selected based on their physical properties and characteristics. Dimensional analyses determine the necessary size of the device, and also play a significant role in determining the materials that will be utilized.

All of these factors affect the cost of any device, which is an important aspect of design. Cost is an especially important consideration, as is the feasibility of replacing a component of the designed structure. For example, a device that replaces a component, such as an actuating lever, can easily be made out of a simple steel rod. If, however, the device is something like the Mars Rover, where replacement of worn parts is not an option, it is far more effective to use a less corrosive, stronger, but more costly material. This could call for titanium to be used to construct movable parts. The historical saying that form follows function is an appropriate rule in the field of applied physics.

Applications and Products

In many ways, applied physics leads to the creation of devices that build other devices. At some point in history, an individual first used a rock to break up another rock or to pound a stick into the ground. This is a simple example of applied physics. In this case, the individual used a specific kind of rock for a specific purpose. In this example, an advancement occurred with the realization that attaching the rock to a stick provided a more effective tool. Applied physics has advanced far beyond this basic example, yet the exact same physical principles apply now with the most elegant of impact devices. It would not be possible to itemize even a small percentage of the applications and products that have resulted from applied physics, and new physical devices are developed each day.

Civil Engineering. Applied physics underpins all physical aspects of human society. It is the basis for the design and construction of the human environment and its supporting infrastructure. The most obvious of these are roads and buildings. These are designed and engineered while considering the forces that they must withstand, both human-made and natural. The highest consideration is given to the science and engineering of materials in regard to the desired end result rather than to the machines and devices that are employed in the actual construction process. The principles of physics involved in the design and construction of supporting structures, such as bridges and high-rise towers, are of primary importance. No less important, however, are the physical systems that support the function of the structure. These include electrical systems, internal movement systems, environmental control systems, monitoring systems, and emergency response systems. All are relevant to a specific aspect of the overall physical construct and must function in coordination with the other systems. Nevertheless, they are all based on specific applications of the same applied physics principles.

Transportation. Transportation is perhaps the single greatest expenditure of human effort. It has produced the modern automotive, air, and railway transportation industries. Applied physics in these areas focuses on the development of more effective and efficient means of controlling the movement of the machine while enhancing the safety of human and nonhuman occupants. While the physical principles by which the various forms of the internal combustion engine function are the same now as when the devices were first invented, the physical processes used in their operation have undergone a great deal of mechanical refinement.

One of these is the manner in which fuel is delivered for combustion. In earlier gasoline-fueled piston engines, fuel was delivered via a mechanical fuel pump and carburetor system that functions on the Venturi principle. This has long since been replaced by constant-pressure fuel pumps and injector systems, and this continues to be enhanced as developers make more refinements based on the physical aspects of delivering a liquid fuel to a specific point at a specific time. Similarly, commercial jet engines, first developed for aircraft during World War II, now utilize the same basic physical principles as did their earliest counterparts. Alterations and developments that have been achieved in the interim have focused on improvement of the operational efficiency of the engines and on enhancement of the physical and combustion properties of the fuels themselves.

In rail transport, the basic structure of a railway train has not changed. It remains a heavy, massive tractor engine that tows a number of containers on very low friction wheel systems. The engines have changed from steam-powered behemoths made up of as many as one-quarter-million parts to modern diesel-electric traction engines of much simpler design.

Driven by the ever-increasing demand for limited resources, this process of refinement for physical efficiency progresses in every aspect of transportation on land, sea, and air. Paradoxically, the area of railway transport that applied physics offers the greatest possibility of advancement. This is with the development of nearly frictionless, magnetic levitation systems upon which modern high-speed bullet trains travel. Physicists continue to work toward the development of materials and systems that will be superconducting at ambient temperatures. Such materials will completely revolutionize not only the transportation sector but also the entire field of applied physics.

Medical. No other area of human endeavor demonstrates the effects of applied physics better than the medical field. The medical applications of applied physics are numerous. They touch every aspect of medical diagnostics and treatment. They also cross over into many other fields of physical science. These include medical imaging, in which X-ray diagnostics, magnetic resonance imaging (MRI), and other forms of spectroscopic analysis have become primary tools of medical diagnostics. All of these devices have become invaluable as medical tools began as devices designed to probe the physical nature of materials.

Spectrographs and spectrometers, which now routinely analyze the specific content of various human sera, were developed initially to examine the specific wavelengths of light being absorbed or emitted by materials. MRI was developed from the standard technique of physical analytical chemistry called nuclear magnetic resonance spectrometry, or NMR. In this methodology, magnetic signals are recorded as they pass through a material sample. Their patterns reveal intimate details about the three-dimensional molecular structure of a given compound. The process of MRI that has developed from this simpler application now permits diagnosticians to view the internal structures and functioning of living systems in real-time. The diagnostic X-ray that has become the single most common method of examining internal biological structures was first used as a way to physically probe the structure of crystals, even though the first practical demonstration of the existence of X-rays by German physicist Wilhelm Röntgen in 1895 was as an image of the bones in his wife's hand.

Military. Applied physics are an inherent part of military applications. No other area of human endeavor so clearly illustrates the double-edged sword that is the nature of applied physics. It both facilitates the most humanitarian of endeavors and the most violent of human behaviors. Ballistics is the area of physics that applies to the motion of bodies moving through a gravitational field. The mathematical equations that describe the motion of a baseball being thrown from center field equally describe the motion of an arrow or a bullet in flight, of the motion of the International Space Station in its orbit, and of the trajectory of a warhead-equipped rocket. The physical principles that have permitted the use of nuclear fission as a source of reliable energy are the same principles that define the functioning of a nuclear warhead.

Military operations strive to reach objectives as quickly and efficiently as possible in restoring order to an embattled area, with as little loss of life and destruction of property as possible. To that end, military research relies heavily on the application of physics in the development of weapons, communications, and surveillance systems.

Digital Electronics. Applied physics has also led to the development of the transistor, commonly attributed to William Shockley, in 1951. Since that time, the development of ever-smaller and more efficient systems based on the semiconductor junction transistor has been rapid and continuous. This has inexorably produced the modern technology of digital electronics and the digital computer. These technologies combine remarkably well to permit the real-time capture and storage of data from the many and various devices employed in medical research and diagnostics, improve the fine control of transportation systems and infrastructure and advance a veritable host of products that are more efficient in their use of energy than are their non-digital counterparts.

Social Context and Future Prospects

Applied physics has become such a fundamental underpinning of modern society that most people are unaware of its relevance. A case in point is the spin-off of technologies from the NASA space program into the realm of everyday life. Common household devices, such as microwave ovens and cell phones, medical devices such as pacemakers and heart monitors, pocket-size and pocket-friendly ultra-sonic devices, and digital technology that permeates modern society were developed through the efforts of applied physics in exploring space. For most laypersons, the term “applied physics” conjures images of high-energy particle accelerators or interplanetary telescopes and probes without the realization that the physical aspect of society is based entirely on principles of applied physics. As these cutting-edge fields of physical research continue, they will continue to spawn new applications that are adapted continually into the overall fabric of modern society.

The areas of society in which applied physics has historically played a role, particularly those involving modern electronics, will continue to develop. Personal computers, mobile phones, and embedded microcontrollers, for example, will continue to grow in power and application while decreasing in size as research reveals new ways of constructing digital logic circuits through new materials and methods. The incorporation of the technology into consumer products, transportation, and other areas of the infrastructure of society is becoming more commonplace. As a result, the control of many human skills can be relegated to the autonomous functioning of the corresponding device—seen most obviously, perhaps, in the rise of self-driving cars and other autonomous vehicles.

The mid-2020s marked the centennial of quantum physics and mechanics. This is the study of the nature of materials smaller than the size of atoms. This led to practical applications in a broad swath of endeavors and the advent of now-essential technologies such as lasers and semiconductors. Considering the relatively recent history of this field, the next century stands to be one of phenomenal advancements in this area of study and applications.

The technologies that have been developed through applied physics permit the automation of many human actions, which, in turn, drives social change. Similarly, the ability for nearly instantaneous communication between persons in any part of the world, which has been provided through applied physics, has the potential to facilitate the peaceful and productive cooperation of large numbers of people toward resolving significant problems.

Bibliography

“A New Century of Quantum Physics.” Nature Review Physics, 6 June 2023, www.nature.com/articles/s42254-023-00600-4. Accessed 3 June 2024.

“Applied Physics Articles from across Nature Portfolio.” Nature Portfolio, www.nature.com/subjects/applied-physics. 3 May 2024, Accessed 3 June 2024.

Askeland, Donald R. The Science and Engineering of Materials. 3rd ed. London: Chapman & Hall, 1998. I

The Britannica Guide to the One Hundred Most Influential Scientists. London: Constable & Robinson, 2008.

Galambos, Conrad. "The Future of Transportation: Where Will We Go?" Geotab, 30 Sept. 2019, www.geotab.com/blog/future-of-transportation. Accessed 29 Jun. 2021.

Ewen, Dale, Neill Schurter, and P. Erik Gundersen. Applied Physics. 11th ed. Pearson, 2017.

Giancoli, Douglas C. Physics for Scientists and Engineers with Modern Physics Toronto, Ont.: Pearson Prentice Hall, 2008.

Sen, P. C. Principles of Electric Machines and Power Electronics. 2nd ed. New York: John Wiley & Sons, 1997.

"12 Innovations That Will Change Health Care in the 2020s." Time, 25 Oct. 2019, time.com/5710295/top-health-innovations. Accessed 29 Jun. 2021.

Valencia, Raymond P., ed. Applied Physics in the Twenty-First Century. New York: Nova Science, 2010. .