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Physics is a fundamental science of nature studying the surrounding reality, mainly addressing the following aspects: the fundamental properties of matter, the structure of matter, the interactions between its constituents, as well as the evolution of matter in space and time.
This science forms a basis for the other natural sciences (chemistry, biology, geography), providing the general laws that govern the universe, at the macroscopic and microscopic level.
In ancient times, all knowledge about the world at that time was contained in a single science called Philosophy after the words Greek language
philo Love
Sophia wisdom
Our philosophy meaning therefore love of wisdom.
From this global knowledge came first natural philosophy, dedicated exclusively to explaining phenomena in the environment.
Modern physics has developed since the 16th-17th centuries, when scientists such as Galileo and Isaac Newton they understood that nature is not only to be contemplated philosophically, and introduced a method of investigation based on experiments and the description of phenomena by laws expressed in the universal language of Mathematics.
Like any science, physics is not based on opinions, but on a rigorous algorithm called scientific method. It comprises the following fundamental steps:
Observation ➔ Formulation of Hypothesis Experimental ➔ Verification ➔ Statement of Law
Note: the careful finding and recording of a phenomenon, as it occurs in nature.
Assumption: formulating a logical assumption or a provisional explanation that tries to answer the question “why does this phenomenon happen?”
Verification (experiment): reproduction of the phenomenon under controlled laboratory conditions, making accurate measurements to see if the hypothesis is confirmed or refuted.
Physical Law: If repeated experiments confirm the hypothesis, it becomes a physical law, i.e. a universal mathematical relationship describing the phenomenon.
Remark: The objects left in the hand fall, that is, they go towards the Earth.
Assumption It was assumed that there was an invisible force of attraction exerted by the Earth on all bodies.
Verification: Bodies of different masses are dropped in different environments (including vacuum), measuring the fall time and acceleration.
Law The validity of the hypothesis was demonstrated, formulating The Law of Universal Attraction newton and the equations of evenly varied rectilinear motion for free fall.
Over time, science develops (knowledge is enriched), it is validated (scientific theories are always confirmed, possibly corrected if necessary) and of course, it is applied in practice in different technical fields (because this is its usefulness).
This evolution is based on two methods:
1. Inductive method (particular to general)
Induction is the method by which one starts from small observations, particular cases or repeated experiments and based on them draw a Overall conclusion (a law valid for all similar cases). It underlies the discovery new laws.
Note 1 Heating an iron bar expands (increases its size, volume).
Note 2 Also, a piece of copper expands, but differently.
Note 3 Aluminum is also expanding.
General conclusion (law): All metals expand when heated. (Shifted from a few examples to a universal rule).
2. Deductive method (general to particular)
Deduction works the other way around: it starts from a general law already known and it applies to a Particular case: to anticipate what's going to happen. It underlies the problem solving, practical applications and scientific forecasts.
General premise (law): We already know that all metals expand on heating.
Particular case: Gold is a metal.
Deductive conclusion: Therefore, a gold wire will lengthen by heating. (The gold wire was no longer tested in the laboratory, but only deduced from the general law).
In scientific research, the two methods complement each other:
Particular Experiments ➔ Induction General ➔ Law ➔ Deduction ➔ Predictions for new cases
- the Summaries of Products Characteristic, labelling, package leaflet and Module 3 proposed by the induction (observing the motion of bodies, including celestial bodies, and conducting experiments), Newton discovered The Law of Universal Attraction.
- the Summaries of Products Characteristic, labelling, package leaflet and Module 3 proposed by the Deduction (using the mathematical formula of that generalized law), astronomers calculated exactly the orbit of Neptune before anyone actually saw it through the telescope.
it cannot be said that
Inductive method represents the way in which science evolves from particular facts and experiments to the enunciation of general laws (discovery of rules).
Deductive method is the application of general laws and mathematical formulas to explain or calculate the behavior of a specific body (application of rules to problems).
Throughout Physics sbutter only 7 fundamental sizes:
|
physical size |
the usual symbol |
sI unit of measurement |
|
measured |
L |
m Metre |
|
masa |
M |
<g id="1">kg</g><g id="2"> <g id="3">Kilogram</g></g> |
|
Time |
T |
%s second |
|
Quantity of substance |
º |
kmol (kilomol) |
|
temperaturę |
T |
K = Kelvin |
|
Electric current intensity. |
I |
<g id="1">A</g><g id="2"> <g id="3">Ampere</g></g> |
|
Luminous intensity |
I |
cd (Candela) |
where SI means International System.
Physical quantities can be divided into two categories: scaling and vectorial.
Scalar physical quantities can be specified only by a single value and the related unit of measurement.
Vector physical quantities additionally requires the specification of a direction and a meaning or can be expressed by a set of numerical values and units of measurement.
Based on these 7 fundamental quantities, a higher number of derived quantitiesCa de exemplu:
|
size |
the usual symbol |
dimensional formula |
sI unit of measurement |
size type |
|
Area |
S |
S L2 |
m2 Square meter |
scale |
|
Volume |
V |
V=L3 |
m3 Cubic metre |
scale |
|
The density |
ρ |
ρ=L-3m |
kg/m3 |
scale |
|
velocity |
v |
v=L∙T-1 |
28 m/s |
vectorial |
|
Acceleration |
a |
a=L∙T-2 |
28 m/s2 |
vectorial |
|
Force |
F |
F=L∙M∙T-2 |
N (Newton or kg·m/s2) |
vectorial |
|
pressure feels |
p |
P/L-1M-T-2 |
Pa (Pascal or N/m2) |
scale |
|
impulse |
p |
p=L∙M∙T-1 |
kg·m/s |
vectorial |
|
Torque |
M |
M L2M-T-2 |
N-m |
vectorial |
|
angular momentum |
L |
L L2M-T-1 |
kg/m2S |
vectorial |
|
Mechanical work. |
L |
L L2M-T-2 |
J (Joules) |
scale |
|
Energy |
E |
E L2M-T-2 |
J (Joules) |
scale |
Dimensional formulas show that derived quantities can be expressed according to fundamental quantities by a relationship of the form: Lαmβt •γ , where α, β, γ are exponents that generally can be positive, negative, zero, integer or not.
