Physics

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Physics, a branch of science, is the study of how the universe works. The word Physics comes from Ancient Greek (ta physika), meaning "the natural things."[1]

Physics is one of the oldest sciences. Since physics tries to describe the entire universe, there is a lot of overlap between different fields of study like biology or chemistry.

Physics is also useful for creating new technology. For example, the radio was only possible because physics gave us a better understanding of how electromagnetic radiation works.

History[change | change source]

Ancient astronomy[change | change source]

Astronomy is the oldest natural science. The Sumerians, Ancient Egyptians, and Indus Valley Civilization all understood how the things in the sky moved since before 3000 BCE. They believed the stars and planets represented their gods, so they kept track of them very well.

A lot of astronomy comes from Mesopotamia, Babylonia, Ancient Egypt, and Ancient Greece. Most names for constellations come from Greek astronomers.

Natural philosophy[change | change source]

Natural philosophy started in Greece around 650 BCE when some philosophers rejected superstition and decided things had to happen for a reason. Leucippus and his student Democritus suggested the idea of the atom around this period.

Physics in the medieval Islamic world[change | change source]

Islamic scholars continued to study Aristotelian physics during the Islamic Golden Age. They also developed an early form of the scientific method.

Scientists like Ibn SahlAl-KindiIbn al-HaythamAl-Farisi and Avicenna worked a lot on optics and vision. In The Book of Optics, Ibn Al-Haitham rejects previous Greek ideas and comes up with a new theory about vision. The book was the first one that studied pinhole cameras, and explained how the eye works. Ibn Al-Haytham also built the first camera obscura hundreds of years before photography was invented.

The Book of Optics affected the way people thought about optics for more than 600 years. It's as influential as Isaac Newton's book by the same name. Thanks to this book, things like eyeglasses, telescopes, cameras, and magnifying glasses were invented.

Classical physics[change | change source]

Physics became a separate field of study after the Scientific Revolution.

Galileo Galilei's experiments helped to create classical physics. He invented the telescope, and then saw that the stars and planets were not perfect. He also (supposedly) dropped some cannonballs from the tower of Pisa and noticed that they hit the ground at the same time, despite one being heavier than the other. Galileo also realized that an object dropped straight down hits the ground at the same time as an object falling and going sideways. This meant that an object in uniform motion (moving in a straight line) is the same as an object that is still, depending on how you look at it.

Sir Isaac Newton used Galileo's ideas to put together his three laws of motion. He then used those laws to prove that they worked for objects on earth and in outer space. Newton hoped that classical mechanics could explain everything, including light (it couldn't).

Newton ran out of math to do physics, so he invented some more math and called it calculus. However, at the same time Gottfried Leibniz also invented calculus and introduced the notation that's used today. Classical mechanics still uses Newton's notation though.

Leonhard Euler added his own laws of motion that worked for rigid bodies (things that don't bend or flop) and not just points. These deal with torque and angular momentum.

Then Joseph Louis Lagrange changed Newtonian mechanics in 1788 to solve more problems. Lagrangian mechanics is used to find the path of a particle that does the least amount of work.

William Rowan Hamilton then changed Lagrangian mechanics in 1833 to solve even more problems. Hamiltonian mechanics made physics more abstract to understand it better, and it eventually led to the development of statistical mechanics and quantum mechanics.

Modern Physics[change | change source]

As research progressed, scientists found things, very big and very small, that classical mechanics couldn't explain.

Classical mechanics predicted that the speed of light varied, but Maxwell's equations said the speed of light stayed the same. Eventually Albert Einstein fixed the problem by coming up with his theory of special relativity. Relativity applies when something is very big, moving very fast, or both.

Max Planck came up with quantum mechanics to explain why metal releases electrons when you shine a light at it, and why stuff just emits radiation. Quantum mechanics applies for very small things like the electrons, protons, and neutrons that make up an atom.

People like Werner Heisenberg, Erwin Schrödinger, and Paul Dirac continued to work on quantum mechanics and eventually we got the Standard Model.

Today physicists are working on getting relativity and quantum mechanics to work together by creating a Grand Unified Theory, or GUT. A GUT would explain everything in the universe.

Definition[change | change source]

Physics is the study of energy and matter in space and time and how they are related to each other. Physicists assume the existence of mass, length, time and electric current and then define (give the meaning of) all other physical quantities in terms of these basic units. Mass, length, time, and electric current are never defined but the standard units used to measure them are always defined. In the International System of Units (abbreviated SI from the French Système International), the kilogram is the basic unit of mass, the metre is the basic unit of length, the second is the basic unit of time, and the ampere is the basic unit of electric current.

In addition to these four units, there are three other ones: the mole, which is the unit of the quantity of matter, the candela which measures the luminous intensity (the power of lighting) and the kelvin, the unit of temperature.

Physics studies how things move, and the forces that make them move. For example, velocity and acceleration are used by physics to show how things move. Also, physicists study the forces of gravity, electricity, magnetism and the forces that hold things together.

Physics studies very large things, and very small things. For instance, physicists can study stars, planets and galaxies but could also study small pieces of matter, such as atoms and electrons.They may also study sound, light and other waves. As well as that, they could examine energy, heat and radioactivity, and even space and time. Physics not only helps people understand how objects move, but how they change form, how they make noise, how hot or cold they will be, and what they are made of at the smallest level.

Physics and Mathematics[change | change source]

Physics is a quantitative science because it is based on measuring with numbers. Mathematics is used in physics to make models that try to guess what will happen in nature. The guesses are compared to the way the real world works. Physicists are always working to make their models of the world better.

Advanced knowledge[change | change source]

General description[change | change source]

Physics is the science of matter and how matter interacts. Matter is any physical material in the universe. Everything is made of matter. Physics is used to describe the physical universe around us, and to predict how it will behave. Physics is the science concerned with the discovery and characterization of the universal laws which govern matter, movement and forces, and space and time, and other features of the natural world.

Breadth and goals of physics[change | change source]

The sweep of physics is broad, from the smallest components of matter and the forces that hold it together, to galaxies and even larger things. There are only four forces that appear to operate over this whole range. However, even these four forces (gravity, electromagnetism, the weak force associated with radioactivity, and the strong force which holds protons and neutrons in an atom together) are believed to be different parts of a single force.

Physics is mainly focused on the goal of making ever simpler, more general, and more accurate rules that define the character and behavior of matter and space itself. One of the major goals of physics is making theories that apply to everything in the universe. In other words, physics can be viewed as the study of those universal laws which define, at the most basic level possible, the behavior of the physical universe.

Physics uses the scientific method[change | change source]

Physics uses the scientific method. That is, data from experiments and observations are collected. Theories which attempt to explain these data are produced. Physics uses these theories to not only describe physical phenomena, but to model physical systems and predict how these physical systems will behave. Physicists then compare these predictions to observations or experimental evidence to show whether the theory is right or wrong.

The theories that are well supported by data and are especially simple and general are sometimes called scientific laws. Of course, all theories, including those known as laws, can be replaced by more accurate and more general laws, when a disagreement with data is found.[2]

Physics is quantitative[change | change source]

Physics is more quantitative than most other sciences. That is, many of the observations in physics may be represented in the form of numerical measurements. Most of the theories in physics use mathematics to express their principles. Most of the predictions from these theories are numerical. This is because of the areas which physics has addressed work better with quantitative approaches than other areas. Sciences also tend to become more quantitative with time as they become more highly developed, and physics is one of the oldest sciences.

Fields of physics[change | change source]

Classical physics normally includes the fields of mechanics, optics, electricity, magnetism, acoustics and thermodynamics. Modern physics is a term normally used to cover fields which rely on quantum theory, including quantum mechanics, atomic physics, nuclear physics, particle physics and condensed matter physics, as well as the more modern fields of general and special relativity. Although this difference can be found in older writings, it is of little new interest as quantum effects are now understood to be of importance even in fields that before were called classical.[3]

Approaches in physics[change | change source]

There are many approaches to studying physics, and many different kinds of activities in physics. There are two main types of activities in physics; the collection of data and the development of theories.

The data in some subfields of physics is amenable to experiment. For example, condensed matter physics and nuclear physics benefit from the ability to perform experiments. Experimental physics focuses mainly on an empirical approach. Sometimes experiments are done to explore nature, and in other cases experiments are performed to produce data to compare with the predictions of theories.

Some other fields in physics like astrophysics and geophysics are mostly observational sciences because most of their data has to be collected passively instead of through experimentation. However, observational programs in these fields use many of the same tools and technology that are used in the experimental subfields of physics.

Theoretical physics often uses quantitative approaches to develop the theories that attempt to explain the data. In this way, theoretical physics often use tools from mathematics. Theoretical physics often can involve creating quantitative predictions of physical theories, and comparing these predictions quantitatively with data. Theoretical physics sometimes creates models of physical systems before data is available to test and support these models. There are many important uses of physics like measuring houses or any measure. Also, it can be used to measure falling objects like planes.

These two main activities in physics, data collection and theory production and testing, use many different skills. This has led to a lot of specialization in physics, and the introduction, development and use of tools from other fields. For example, theoretical physicists use mathematics and numerical analysis and statistics and probability and computer software in their work. Experimental physicists develop instruments and techniques for collecting data, using engineering and computer technology and many other fields of technology. Often the tools from these other areas are not quite appropriate for the needs of physics, and need to be changed or more advanced versions have to be made.

Physicists[change | change source]

There are many famous physicists. Isaac Newton studied gravity. Galileo Galilei studied light and how planets moved. Albert Einstein made a theory for how light can make electrons move, and studied how gravity affects light and space. James Clerk Maxwell proved that light is a type of electromagnetic wave.

Prominent theoretical physicists[change | change source]

Famous theoretical physicists include

Related pages[change | change source]

References[change | change source]

  1. "Online Etymology Dictionary". http://www.etymonline.com/index.php?term=physics&allowed_in_frame=0.
  2. An equation (e.g., f = m a) is called a "law" when there are clear empirical results that substantiate it.
  3. Different people, however, have different definitions of what they regard physics to be, and another common definition is that, "physics is the science of nature" [1,2,3,4,5,6].

Other websites[change | change source]