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Physics is a science of nature, as its name indicates, which comes from the Greek:
physis means nature;
physikos means of nature.
Physics generally studies inanimate matter, the properties of matter, and the evolution of matter.
The main object of study of Physics are the bodies. A body can be any object, of any size, in any state of aggregation:
• solid, artificially made objects, such as parts, devices, mechanisms;
• solid objects encountered in nature: rocks, wood;
• amounts of liquids, however small or large:
◦ water in a glass;
◦ all the water of a lake, sea or ocean;
• quantities of gases, however small or large:
◦ air contained in a balloon;
◦ all terrestrial atmosphere;
• celestial bodies: planets, stars;
• microscopic particles: molecules, atoms, protons, neutrons, electrons, ...
The bodies have various properties, which can be classified into:
• dimensions (length, width, height, thickness, diameter, ...), perimeter, area, volume – all of which 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 time;
• speed – shows how fast a body is moving;
• mass – expresses in a certain way the amount of substance and is measured in kg;
• weight – shows how hard the 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 on Earth, but on the Moon it becomes much lighter, with only 1.63N.
Under certain circumstances a body no longer has weight, but retains its mass, so mass and weight are different notions, which should not be confused.
The density
HARDNESS
• chemical composition – what substances it is made of and in what proportions;
Humidity
• thermal state – temperature;
• aggregation state: solid, liquid, gaseous, plasma;
• melting, boiling temperature;
Pressure
colour
• surface texture;
• surface appearance: glossy, matte;
• taste;
"smell",
• physical wear – if tools, tools;
• obsolescence – whether it is about various devices or installations, which are or not technologically obsolete;
• moral traits: benevolence, ill will, generosity, stinginess – if it is about people;
• aesthetic value: beautiful, ugly;
They are the properties that bodies have objectively, that is, regardless of the subjective impression of the observer. The above list contains almost entirely physical properties. We've marked property exceptions that are not physical properties and remain in the general property category.
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 shall be specified, but not measured. It's a physical property, but not a physical size.
Objects can be weighed. Mass and weight are physical sizes.
Even color can be expressed in a quantitative way, that is, 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, there is no way to measure them.
În general, corpurile nu sunt izolate, ci alcătuiesc sisteme, în interiorul cărora corpurile interacționează, adică se influențează reciproc (fiecare din corpuri acționează asupra celorlalte). Un exemplu este sistemul solar, alcătuit din Soare și planete. Planetele se învârt în jurul Soarelui. De ce? Fiindcă au loc interacțiuni între Soare și planete: există o atracție reciprocă între Soare și planete. Altfel, planetele nu ar rămâne în sistemul solar, ci s-ar împrăștia prin Univers. Interacțiunile corpurilor sunt hotărâtoare pentru o anumită evoluție a întregului sistem.
Interactions are also physical properties of bodies.
In general, the bodies around us do not remain unchanged over time. They change their properties: they change their position (they move), they change their shape, they melt, they evaporate, they condense, they crystallize, they emit light, heat...
These changes in physical properties are called physical phenomena or physical processes. Examples:
• fall of bodies, movement of planets;
• water freezing, ice melting; vapor condensation, water evaporation;
• lightning, lightning;
• light emission, light reflection, rainbow;
Physical phenomena occur mainly due to the interactions of bodies.
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, as the bodies have greater mass and are closer to each other.
Knowledge of physical laws helps to predict physical phenomena.
Physical phenomena occur all around us, but they can be reproduced in a specially arranged space, called a laboratory, using experimental means. The purpose of the experiment is to observe, to better understand the physical laws, to find useful applications of these laws and eventually to further develop this science.
Depending on the nature of the phenomena studied, the content of Physics can be divided into thematic areas (chapters):
• Mechanical phenomena (mechanical);
• Thermal phenomena (thermodynamics);
• Electrical and magnetic phenomena (electricity and magnetism);
• Optical phenomena (optics).
We have listed here only the chapters that are studied at level I.
Logically, the study of Physics begins with mechanics.
Physics has mainly technical applications. All machines, mechanisms, appliances operate on the basis of physical laws. Through the application of physical laws, natural phenomena are used usefully.
Examples:
• Lightning and lightning are frightening natural phenomena, but at present these natural phenomena are widely used in technical applications:
◦ Numerous devices produce electric sparks to ignite the fire, the sparks being miniature lightning;
◦ Arc welding machines are used. They produce a kind of lightning with a longer duration, in order to be able to melt and weld metals;
◦ In gas-discharge luminaires, controlled and sustained electrical discharges occur, which convert the gas into plasma and light is obtained, because the plasma is luminous.
• Microparticles (protons, electrons, atoms, molecules) attract or repel each other and thus form bonds with each other. These interactions also cause forces to appear between larger objects:
◦ magnets attract or repel;
electrified ◦ objects are attracted or rejected;
◦ the electric current produces magnetic effects;
◦ the heated gases pressurize.
Motors (electrical or thermal) operate by using the forces that occur in such cases.
