Introduction

Physics is a science of nature, as its name indicates, which comes from the Greek language:

physis means nature;
physikos means of nature.

Physics generally studies nonliving matter, the properties of matter, and the evolution of matter.

Fundamentals

The main object of study of Physics are bodies. A body it can be any object, of any size, in any state of aggregation:

• solid objects, made artificially, such as parts, devices, mechanisms;

• solid objects found in nature: rocks, wood;

• amounts of liquids, however small or large:

◦ water from a glass;

◦ all water of a lake, sea or ocean;

• quantities of gas, however small or large:

◦ the air contained in a balloon;

◦ all terrestrial atmosphere;

• celestial bodies: planets, stars;

• microscopic particles: molecules, atoms, protons, neutrons, electrons, ...

Bodies have various properties, which can be classified into:

1. general properties:

• dimensions (length, width, height, thickness, diameter, ...), perimeter, area, volume - all these can be called geometric measures;

• geometric shape:

◦ regular: cube, parallelepiped, prism, pyramid, cylinder, cone, sphere;

◦ irregular;

• position – the place in space, where a body is at a given moment;

• speed – shows how fast a body moves;

• mass – expresses in a certain way the amount of substance and is measured in kg;

• weight – shows how strongly the respective object is pulled down by the Earth or possibly another celestial body. Weight is a type of force and is measured in N (Newtons). An object with a mass of 1kg has a weight of 9.81N here on Earth, but on the Moon it becomes much lighter, having only 1.63N.

In certain circumstances a body no longer has weight, but retains its mass, so mass and weight are different notions, which should not be confused.

• density;

• hardness;

• chemical composition - what substances it is made of and in what proportions;

• humidity;

• thermal state – temperature;

• state of aggregation: solid, liquid, gaseous, plasma;

• melting, boiling temperature;

• pressure;

• color;

• surface texture;

• surface appearance: glossy, matte;

• the taste;

• the smell;

• physical wear and tear – in the case of tools;

• moral wear and tear – if it concerns various devices or installations, which are technologically outdated or not;

• moral traits: benevolence, benevolence, generosity, stinginess – if it is about people;

• aesthetic value: beautiful, ugly;

2. physical properties:

They are the properties that bodies have objectively, that is, regardless of the subjective impression of the one who observes them. The above list contains almost entirely physical properties. I marked the exceptions of properties that they are not physical properties and remain in the category of general properties.

3. physical sizes:

They are those physical properties that can be measured and thus expressed quantitatively:

All geometric measures (length, width, height, area, volume) can be measured, so they are physical quantities.

The geometric shape is specified, but not measured. It is a physical property, but not a physical quantity.

Objects can be weighed. Mass and weight are physical quantities.

Even color can be expressed in a quantitative way, meaning it can be measured in some way. For example, blue light has a wavelength of 450nm, green has 550nm, and red has 650nm. Close values such as 440nm, 560nm or 640nm correspond to certain shades of blue, green, red.

Taste and smell are not considered physical quantities, as there is no way to measure them.

Body systems

In general, the bodies are not isolated, but make up systems, within which the bodies interact, that is, they influence each other (each of the bodies acts on the others). An example is the solar system, made up of the Sun and planets. The planets revolve around the Sun. Why? Because there are interactions between the Sun and the planets: there is a mutual attraction between the Sun and the planets. Otherwise, the planets would not remain in the solar system, but would be scattered throughout the Universe. The interactions of the bodies are decisive for a certain evolution of the whole system.

Interactions are also physical properties of bodies.

Physical phenomena

In general, the bodies around us do not remain unchanged over time. They change their properties: change their position (move), change their shape, melt, evaporate, condense, crystallize, emit light, heat...

These changes in physical properties are called physical phenomena or physical processes. Examples:

• the fall of bodies, the movement of the planets;

• freezing of water, melting of ice; vapor condensation, water evaporation;

• lightning, thunder;

• light emission, light reflection, rainbow;

Physical phenomena occur mainly due to the interactions of bodies.

Physical laws

Physical phenomena do not occur randomly, but under certain conditions and according to certain rules, which are called physical laws. Physical laws are scientific truths established after repeated observations of physical phenomena, generalizations, conclusions, verifications.

An example is the law of gravity. This law states that:

• all bodies in the Universe have the property that they attract each other;

• the stronger the attraction, the more mass the bodies are and the closer they are to each other.

Knowledge of physical laws helps to predict physical phenomena.

The physical experiment

Physical phenomena occur all around us, but they can be reproduced in a specially designed space, called a laboratory, using experimental means. The purpose of the experiment is to observe, to better understand physical laws, to find useful applications of these laws, and eventually to further develop this science.

Fields of Physics

Depending on the nature of the studied phenomena, the content of Physics can be divided into thematic areas (chapters):

• Mechanical phenomena (mechanics);

• Thermal phenomena (thermodynamics);

• Electric and magnetic phenomena (electricity and magnetism);

• Optical phenomena (optics).

I have listed here only the chapters that are studied at level I.

Logically, the study of Physics begins with mechanics.

The Utility of Physics

Physics has mainly technical applications. All machines, mechanisms, devices work on the basis of physical laws. By applying physical laws, natural phenomena are put to good use.

Examples:

• Lightning and lightning are frightening natural phenomena, but nowadays these natural phenomena are widely used in technical applications:

◦ Many devices produce electrical sparks to start a fire, the sparks being miniature lightning bolts;

◦ Electric arc welding machines are used. They produce a kind of lightning of longer duration, so that it is possible to melt and weld metals;

◦ In gas discharge lighting fixtures, controlled and sustained electrical discharges are produced, which transform the gas into plasma and produce light, because plasma is luminous.

• Microparticles (protons, electrons, atoms, molecules) attract or repel each other and thus form bonds between them. These interactions also cause forces to appear between larger objects:

◦ magnets attract or repel;

◦ electrified objects attract or repel;

◦ electric current produces magnetic effects;

◦ heated gases create pressure.

Engines (electrical or thermal) work by using the forces that arise in such cases.