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What is Physics? - Definition, Branches, Fundamentals & Topics

What is Physics? - Definition, Branches, Fundamentals & Topics
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  • 0:03 Origins of Physics
  • 1:57 Branches of Physics
  • 6:55 Fundamental Subject Areas
  • 13:30 Lesson Summary
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Lesson Transcript
Instructor: Damien Howard

Damien has a master's degree in physics and has taught physics lab to college students.

Get a basic overview of modern physics. Learn about the science's origins, the fields of physics being worked in today, and the major subject areas taught in general physics courses.

Origins of Physics and Definition

Have you ever wondered how your microwave heats the food in it, or how you can possibly be talking with someone hundreds of miles away on your cell phone? These modern devices did not just spring out of thin air. They are all based on the properties of the world around us. By studying and learning about these properties, we can then harness them for our use in devices such as microwaves and cell phones.

The process of studying these properties of the world around us is what we do with physics. Both these examples work because of our understanding of electromagnetic waves that we have learned from physics. Thanks to physics, we've learned to use different properties of electromagnetic waves to cook food, send our voices across the Earth for others to hear, and many other uses in modern society.

Physics, however, is not a science that is just now being used for recent inventions. In fact, it is one of the oldest of the natural sciences. The word 'physics' itself can be traced back to the Greek word phusika, meaning 'natural things.' It was in the ancient Greeks' study of philosophy and the natural world around them that the science of physics was first born. Asking philosophical questions about why the world works the way it does led to investigation of the world in order to determine those answers. Since then, the definition of physics has changed from the more vague philosophical beginnings as a study of nature to the study of matter and energy and how they interact with one another. While this is more of a concrete definition, it still allows for a vast amount of subjects to fall under its purview, such as mechanics, optics, electricity, magnetism, and many others.

Branches of Physics

As previously stated, the definition of physics allows for many subjects to fall under it. Fields within physics may study things as large as the universe itself, or particles so small you can't see them in a traditional optical microscope. Here we'll go over some of the physics fields scientists are working in today.

Let's start with the large scale, examining those fields that are looking beyond our planet and into the depths of space. Cosmology is the field of physics that studies the entirety of the universe as a single entity. Cosmologists strive to understand the origin of our universe, how it has changed over time, and what the future might hold for it.

Then there is astrophysics, which also looks to understand how the universe works. Instead of looking at it as one whole, astrophysicists often break the universe down into smaller chunks. An astrophysicist might study the properties of everything from entire clusters of galaxies down to individual stars, planets, or even smaller bodies moving through space. One example of something an astrophysicist might do is preemptively calculate the flight path of large asteroids in our solar system to see if the Earth is in danger of being hit by one.

Now we'll move from space down to our own planet with geophysics. Geophysicists study the physical properties of the Earth and its immediate surroundings. They study parts of the Earth, such as plate tectonics, the magnetic field, or the fluid mechanics of the oceans and the atmosphere. Geophysicists might use this data they've collected for purposes such as determining where valuable metals and minerals can be mined, or for making sure the ground of a construction project is safe to build on.

While geophysics looks at what the Earth is made of, biophysics is focused on the creatures living on Earth. Biophysicists research anything ranging from whole ecosystems down to the internal processes and individual cells of a single living organism. Biophysics has helped us develop technologies such as CAT scans and MRIs that get images of the inside of our body, without invasive surgical procedures, in order to assist doctors with their work. As might be guessed from their names, geophysics and biophysics are both multidisciplinary fields. Geophysics also incorporates elements of geology and meteorology, and biophysics uses concepts from biology. What distinguishes geophysics and biophysics from the non-physics based fields is that they have a heavy focus on using a quantitative approach with computational and mathematical methods to back their research.

We've now scaled in size from studying the entirety of the universe with cosmology down to individual cells with biophysics, but we aren't done yet. Let's go even smaller to the individual atoms that make up our universe with atomic physics. Atomic physics covers the physical properties of individual atoms, as well as atomic interactions with other atoms, electric fields, and magnetic fields.

Yet we can go even smaller than individual atoms with the field of nuclear physics. Nuclear physics doesn't look at the whole atom but concerns itself only with the nucleus of the atom. Nuclear physics covers topics such as radioactive decay, nuclear fusion, and nuclear fission. Famously, this is the field of physics that brought us the atomic bomb and harnessed nuclear energy in power plants.

Finally, we'll end our scaling down with photonics. A photon is a single quantum of electromagnetic energy, which for simplicity's sake is often treated as a particle of light even though it is distinctly not a particle. It is one of the smallest known existing things in the universe. Photonics studies the physical properties of these photons with a focus on using them as a transmitter of information in a similar way that electrons are currently used in modern devices.

These branches of physics we've gone over are certainly not all that exist out there. Just to name a few more, there are theoretical physics, plasma physics, condensed matter physics, etc. But the ones we've gone over should give you a grasp of how wide of a field physics is. It encompasses both the biggest and smallest things you can possibly imagine.

The Fundamental Subject Areas

While the different branches of physics are very diverse, there are a number of core fundamental topics that every physicist learns regardless of what field she or he ends up working in. Here we are going to have a brief overview of those topics.

Classical mechanics is the foundation on which modern physics is based. It focuses on the motion of particles in a 3-dimensional system and has its basis in the three laws of motion defined by Isaac Newton. Of all the fundamental subject areas, classical mechanics is the most easily relatable to the world around us. It deals largely with the physical properties of solid objects that can be seen by the naked eye, touched, and held in your hand.

You can learn how far a ball will fly after being hit by a baseball bat, how many times a pendulum will swing back and forth before it stops, how the breaks in your car or bicycle work, and much more. Here is where everyone begins their journey into physics and what the majority of your first physics course will be focused on. You'll learn about the motion and interaction of large particles in one, two, and three dimensions, exploring topics such as velocity, acceleration, mass, force, work, energy, and momentum.

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