Physical Quantities and Their Measurements

Physical Quantities and Their Measurements

Learning Outcome

  • The scope and gradual development of physics.
  • The objectives of physics.
  • The physical quantities as the origin of physics. 
  • The measurement and necessity of units.
  • The difference between fundamental and derived quantities.


The branch of science which deals with matter and energy is called physics. The main objectives of physics are to establish the relation between matter and energy and to express it quantitatively on the basis of observation, experimentation, and analysis.

Scope of Physics

Physics is the key to all science. It is the fundamental branch of science because the foundation of other subjects is based on the principles of physics. For example, the principle of conservation of energy is a basic principle of physics used to explain the wide range of science starting from the structure of atoms to weather forecasting. Starting from Engineering to Medical Science, Astronomy to Oceanology, Biology to Psychology the instruments of Physics are used. 

For the systematic study of physics, we can divide it into the following branches: 

(1) Mechanics 

(2) Heat and thermodynamics 

(3) Sound 

(4) Optics 

(5) Electricity and Magnetism 

(6) Solid State Physics 

(7) Atomic Physics 

(8) Nuclear Physics 

(9) Quantum Physics and 

(10) Electronics

Development of Physics

Modern civilization is the product of science. Behind this development of science, there are untiring efforts, discoveries, and innovations of scientists. Science has no national or political boundaries. The growth, development, and benefit of science are enjoyed by all people of all nations. From ancient time scientist have been contributing to the development of science. In this lesson, we will try to mention the contributions of physicists. Thales (624-569 B.C) is famous for his predictions regarding solar eclipse. He also knew about the magnetic properties of loadstone. Pythagoras (527-497 B.C) is a memorable name in the history of science. Besides the invention of several Geometric theorems, he made a longer-lasting contribution through his works on vibrating string. He was given several Geometric theorems. Moreover, he made long lasting contributions through his works on vibrating strings. The present scales of musical instruments and music are partially the contributions of his research on the vibration of strings. 

Greek philosopher Democritus (460-370 B.C) gave the idea that matter consists of indivisible units. He called it an atom. His concept about the atom was significant even though it is completely different from the present concept. Greek scientist Archimedes (287-212 B.C) discovered the principles of the lever and the law of upward force acting on bodies immersed in liquid and was able to determine the impurity in metals. He also knew the technique of setting fire by concentrating sun rays with the help of spherical mirrors. 

After Archimedes, scientific discoveries advanced rather slowly for a few centuries. In fact, scientific discoveries did not revive in Europe before the thirteenth century. During this time West European civilization particularly adopted the trends of the Byzantine and Muslim civilization in the pursuit of knowledge. The Arabs were also particularly advanced in Science, Mathematics, Astronomy, Chemistry, and Medical Science. During this time the contribution of Ibne-Al-Haithan (965-1039 A.D) and Al-Hazen (965-1038 A.D) may be particularly mentioned for their theories of light, a branch of physics.

Ptolemy (127-151 A.D) and other earlier scientists believed that the eyes themselves send light rays to see an object. Al-Hazen contradicted this view and asserted that we see an object because light rays from the object fall on our eyes. Experiments with magnifying glass brought him near to the modern theory of convex lens. Al-Masudi (896-956 A.D) wrote an encyclopedia on the History of Nature in which the name of Windmill was first mentioned. At present many countries of the world produce electricity by using this windmill.

Roger Bacon (1214-1294 A.D) was the pioneer of experimental scientific methods. According to him, all scientific truths should be verified through observations and experiments. At the end of the fifteenth century, Leonardo de Vinci (1452-1519 A.D) made a model of an airplane by observing the act of flying birds. Although he was a painter, he had considerable knowledge of mechanics. As a result, he was able to invent efficiently some common instruments. During the Galileo-Newtonian age and even before that time a few very important scientists, although small in number were born. They contributed a lot to the advancement of science too. Dr. Gilbert (1540-1603 A.D) is unforgettable for his extensive research and theory on magnetism. Snell (1591- 1626 A.D) of Germany discovered the laws of refraction of light. Huygen (1626-1695 A.D) reviewed the motion of a pendulum, developed the mechanical device of clocks, and invented the wave theory of light. Robert Hook (1635-1703 A.D) strove to find out the elastic properties of bodies. Robert Boyle (1627-1691 A.D) conducted experiments to find out the properties of gases at different pressures. Von Guerick (1602-1686 A.D) invented the air pump. Romer (1644-1710 A.D) measured the velocity of light by studying the eclipse of a satellite of Jupiter, but none of his contemporary scientists believed that the velocity of light could be so high.

Kepler (1571-1630 A.D) presented three laws for a general mathematical explanation of the concept of the solar-centered theory of Copernicus. Kepler’s success was based on his assumption of an elliptical orbit as opposed to the conventional circular orbit. He verified the validity of his mathematical laws about the orbits of the planets with the data collected through observation by his teacher Tychobrahe (1546-1601 A.D). 

The inception of the modern scientific method was made by a famous Italian scientist Galileo (1564-1642 A.D). He showed for the first time that the observations, experimentations, and definitions of physical quantities systematically and the determination of relations among them are the basic foundation of scientific works. 

Galileo introduced the scientific trends of developing mathematical theory and verifying its authenticity through experiments. Later, Newton (1642-1727 A.D) gave it a complete shape. Galileo defined displacement, motion, acceleration, time, etc., and determined relations among them. Consequently, he discovered the laws of falling bodies and established the foundation of statics. Newton by his versatile genius discovered mechanics and the three famous laws of mechanics and the law of universal gravitation. He also made contributions to optics, heat, and sound. He invented calculus, a new branch of mathematics.

The discovery and inventions of the eighteenth and nineteenth-century paved the way for 
Europe to the industrial revolution. The steam engine of James Watt (1736-1819 A.D) played a vital role in the industrial revolution. Hans Christian Oersted (1777-1851 A.D) demonstrated the magnetic effect of current. This discovery led Michael Faraday (1791- 1867 A.D), Henry (1797-1879 A.D), and Lenz (1804-1865 A.D) towards discovering the fact that the magnetic effect produces an electric current. In fact, this was a discovery of the process of converting mechanical energy into electrical energy.

In 1864 James Clark Maxwell (1831-1879 A.D) demonstrated that light is one kind of electromagnetic wave. He established the electromagnetic theory by combining electric and magnetic fields. A similar kind of radiation was also discovered and produced in 1888 by Heinrich Hertz (1857-1894 A.D). Using the same kind of waves in 1896, Marconi (1874-1937 A.D) discovered the method of sending a signal through ″Morse code″ to far off distance. Before him, Sir Jagadish Chandra Basu (1858-1937 A.D) was able to send energy from one place to another through electromagnetic waves. In this way, radio communication was developed. By the end of the nineteenth century Roentgen (1845-1923 A.D) discovered x-rays and Becquerel (1852-1908 A.D) discovered the radio activity of uranium.

In the twentieth century surprising advancement took place in the field of physics. Max Planck (1858-1947 A.D) discovered quantum theory of radiation. Albert Einstein (1879- 1955 A.D) invented theory of relativity. These two theories not only explained the previous experimental result but also made some predictions which were experimentally verified. Ernest Rutherford’s (1871-1937 A.D) nuclear theory regarding atoms and Neill Bohr’s (1885-1962 A.D) concept of electron layers in the hydrogen atoms were very important step of atomic physics.

The next important discovery was made in 1938. At this time Otto Hann (1879-1968 A.D) and Stresemann (1902-1980 A.D) found out that nucleus was fissionable. Due to fission a nucleus of large mass number splits up into two nuclei of approximately equal mass number and a part of its mass is converted into energy as a result of which atom bomb and nuclear reactor are invented. The amount of energy we are getting at present from the nucleus is huge compared to the energy obtained from all the sources in the past. Day by day nuclear energy is becoming the principal source of energy. In this century quantum theory of the relativity etc. was developed in the field of theoretical physics. Satyendranath Basu (1894-1974 A.D) professor of physics, University of Dhaka made important contribution on theoretical physics. He demonstrated a comparatively correct form of Planck’s quantum theory. His theory is known as Bose-Einstein’s statistics. As recognition of his contribution one kind of elementary particle is named after him and is called Boson. Three nobel laureate physicist Prof. Abdus Salam (1926- 1996 A.D) of Pakistan, Sheldon Glasso (1932-) and Stevan Wienberg (1933-) of United States made outstanding contribution by discovering weak electric force in unifying the elementary particles in unified field theory. Prior to that nobel laureate physicist Chandra Shekhar Ramon (1888-1970 A.D) discovered Ramon effect. Physics has made significant contribution in the progress of medical science in twentieth century. By using radio isotopes along with the discovery of numerous equipments physics has contributed to medical science. Another advancement of physics in twentieth century is exploration in the space. The contribution of physics lies in landing human footprint on the moon along with the staying of months after months in space station and exploration on the Mars.

Artificial satellite has contributed to forecast weather and made communication easy. Moreover electronics has already brought about revolution in our daily life and changed our life style. Now a days radio, television, digital camera, mobile phone, i-pad and computer are used almost in every house. Various electronics instruments have developed human’s work ability to a great extent.

In nineteenth century physics played a vital role for the advancement of medical science. Outstanding contribution of physics in the field of medical science lies in inventing different instrument along with radio isotope for the prevention of diseases. Another advancement of physics in the twentieth century is the exploration in the space. 

Objectives of Physics

Physics unearths the mystery of nature: Physics is the fundamental branch of science because its principles are the basis of other branches of science. For example, the principle of conservation of energy is a principle of physics used to explain the wide range of science starting from the structure of atoms to weather forecasting.

Although the main function of physics is to study matter and energy, the main objective of physics is to realize the rules of nature as well as unearthing the mystery of nature. At the beginning of the twentieth century, physicists discovered that electrons revolve around the positively charged nucleus of an atom. Subsequent experiments proved that the nucleus consists of protons and neutrons. Now the physicists have discovered that protons and neutrons are formed of smaller particles.

The study of physics helps not only to understand and explain natural events but also its application plays a vital role in other branches of science. At present physics is at the center probably because of its application in other branches of science. The discovery of electron at the end of the ninetieth century made possible to invent the electron microscope which has brought about a revolution in material science and Cytology.

In physics, there is the development of theories and application mathematics at the same time it has practical application and engineering application too. Physics is very essential to give fundamental explanation and form an idea about Chemistry, Geology, Astronomy, Meteorology, etc. In addition, there is a wide application of methodology and instruments of physics in Biology, Oceanology, Psychology, and Medical Science.

Physics describes the laws of nature: The natural world that we live in follows certain laws e.g. Newton’s law of gravitation, the law of conservation of energy, etc. Since our childhood, we have been acquiring these laws through our personal experiences which are very essential for our life. We cannot change the function and laws of nature but can utilize them. For their proper utilization, we need sufficient knowledge about them. Moreover, physics is the science that studies on this earth for innovation. 

Development of technology results from the proper application of fundamental laws of physics: We have to have knowledge about the fundamental laws of physics if want to know how television works, the rocket flies in the space, artificial satellite revolves around the earth, mobile phone functions, submarine remain submerged into water and how by using the internet the whole world can be explored in a moment. The discovered laws of physics pave the way to invent these technologies.

The study of physics is perfect human training: We can achieve new ideas by the study of physics. Physics instructs on how to think, show cause, how to put argument, how to utilize logic and mathematics. It stimulates our imagination and develops the power of thinking. 

Physics teaches how to carry out observation: We can develop our capability of observation. We can also learn how to carry out systematic observations by studying physics properly.


About Me

Md. Saifur Rahman

B.Sc (Honors), M.Sc (Chemistry)

Former Principal of South Point School and College, Dinajpur.

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