A Brief History of Physics and Measurement
History of Physics
Physics is the natural science that studies matter, its motion and behavior through space and time, and the related entities of energy and force.
Key Figures in Physics History
- Aristotle (384-322 BC) tried to establish general principles that ruled the behavior of natural bodies, both living and inanimate, also celestial and terrestrial bodies, applying concepts like motion, change of place, and change of size or number.
- Archimedes (287-212 BC) is considered one of the greatest mathematicians of ancient times. He was one of the first to apply math to physical phenomena, being the father of hydrostatics and discovering the buoyancy principle which bears his name.
- Galileo Galilei (1564-1642) is considered the father of modern physics. His experiments and studies of the motion of bodies were precursors of classical mechanics.
- Isaac Newton (1642-1726) established motion laws that now bear his last name and also the principles of universal gravitation. He also contributed to optics and the development of calculus.
- James Clerk Maxwell (1831-1879) formulated the electromagnetic theory that unifies the concepts of electricity and magnetism. The equations that bear his last name are the foundation of radio waves and other technological achievements.
- Albert Einstein (1879-1955) developed the theory of relativity, discovered the photoelectric effect, and contributed to quantum theory.
Astronomy, one of the areas of physics, has been studied since ancient times. It was considered part of philosophy before becoming a modern science.
Branches of Physics
Physics aims to provide knowledge, from basic to complex. It is broadly divided into:
- Classical Physics (developed between the 17th and 19th centuries): Deals with velocities small compared to the speed of light.
- Modern Physics (developed almost entirely during the 20th century): Considers quantum and relativity theories. It deals with velocities near the speed of light.
Measurement and Unit Systems
A physical quantity is a quantifiable or assignable property linked to a phenomenon, body, or substance. A physical quantity is measured by comparing it with a previously known standard. Examples include weight, mass, length, and time.
Standard: The Standard Model of particle physics describes three of the four known fundamental forces (electromagnetic, weak, and strong interactions, excluding gravity). A standard is a permanent physical record, or easy to determine, of the quantity that implies a particular measurement unit.
Magnitude: The magnitude of a physical quantity is defined with a number and a unit of measure (example: 20 meters, 40 liters).
Unit: A unit is a particular physical quantity used to compare other quantities of the same kind to show their value.
Measuring is a process that consists in comparing an unknown magnitude with another already known in the same unit of measure.
- Direct Measurement: The unknown magnitude is measured with an instrument of the same magnitude (e.g., measuring length with a ruler).
- Indirect Measurement: The unknown magnitude is measured through mathematical calculations performed with quantities obtained from direct measurements (e.g., calculating speed as distance/time, where distance is measured with road markers and time with a clock).
International System of Units (SI)
The International System of Units (SI), based on the metric system, is the most used unit system worldwide. It is regulated by several bodies located in Paris, France, including the International Committee of Weights and Measures.
Fundamental SI Units
- Meter: The length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.
- Kilogram: The unit of mass; it is equal to the mass of the international prototype of the kilogram (this is the only standard that requires a physical comparison to be valid).
- Second: The time needed for 9,192,631,770 vibrations of a cesium atom.
Derived Units: Combinations of fundamental units (e.g., volume, pressure, speed, and force).
Scientific Notation: Provides a concise method to represent very large or very small numbers.