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Mechanics studies the motion of macroscopic bodies, the causes of motions, as well as the conditions under which macroscopic bodies are in equilibrium.
Macroscopic bodies are generally objects or beings that can be directly observed or perceived without special observation tools: rocks, wood, plants, animals, mechanisms and components of mechanisms, celestial bodies...
Macroscopic bodies can be made up of solid, liquid or gaseous substances, in quantities large enough to disregard the discontinuous, microscopic structure of the substance: metal or synthetic parts, water in a vessel, water droplets, the atmosphere of a planet, air in a balloon,... Within mechanics any material of which a body is made is treated as if it were a continuous medium, without microscopic structure.
Mechanical phenomena can be directly observed or perceived: rest and movement of various bodies, deformation of bodies, flow of liquids and gases, propagation of sounds or various other mechanical waves,…
In all the mechanics sbutter only 3 fundamental sizes:
|
size |
The |
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 |
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 specifying a direction and meaning.
All 3 fundamental quantities above are of the scalar type.
Based on these 3 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.
