|
|
|
|
|||
Mechanics studies the motion of macroscopic bodies, the causes of motion, and the conditions under which macroscopic bodies are in equilibrium.
Macroscopic bodies are generally objects or beings, which can be observed or perceived directly, without special instruments of observation: 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 so that the discontinuous, microscopic structure of the substance is not relevant: metallic or synthetic material parts, water in a bowl, water drops, the atmosphere of a planet, the air in a balloon,... In mechanics, any material from which a body is made is treated as if it were a continuous medium, without microscopic structure.
Mechanical phenomena can be observed or perceived directly: the rest and movement of various bodies, the deformation of bodies, the flow of liquids and gases, the propagation of sounds or various other mechanical waves,...
In all mechanics sbutter only 3 fundamental quantities:
|
size |
SYMBOL |
SI unit of measure |
|
the length |
L |
m (meter) |
|
mass |
M |
kg (kilogram) |
|
time |
T |
s (second) |
where SI means The International System.
Physical quantities can be divided into two categories: scalar and vector.
Scalar physical quantities they can only be specified by a single value and the related unit of measure.
Physical vector quantities it additionally requires the specification of a direction and a meaning.
All 3 fundamental quantities above are scalar type.
Based on these 3 fundamental sizes, a larger number of derived quantities, such as:
|
size |
the usual symbol |
dimensional formula |
SI unit of measure |
size type |
|
area |
S |
S=L2 |
m2 (square meter) |
scalar |
|
VOLUME |
V |
V=L3 |
m3 (cubic meter) |
scalar |
|
the density |
ρ |
ρ=L-3∙M |
kg/m3 |
scalar |
|
speed |
v |
v=L∙T-1 |
m/s |
VECTORIAL |
|
acceleration |
a |
a=L∙T-2 |
m/s2 |
VECTORIAL |
|
force |
F |
F=L∙M∙T-2 |
N (Newton or kg·m/s2) |
VECTORIAL |
|
PRESSURE |
p |
p=L-1∙M∙T-2 |
Pa (Pascal or N/m2) |
scalar |
|
impulse |
p |
p=L∙M∙T-1 |
kg·m/s |
VECTORIAL |
|
moment of force |
M |
M=L2∙M∙T-2 |
N·m |
VECTORIAL |
|
the kinetic moment |
L |
L=L2∙M∙T-1 |
kg·m2/s |
VECTORIAL |
|
mechanical work |
L |
L=L2∙M∙T-2 |
J (Joules) |
scalar |
|
power |
E |
E=L2∙M∙T-2 |
J (Joules) |
scalar |
The dimensional formulas show that the derived quantities can be expressed in terms of the fundamental quantities through a relationship of the form: Lα∙Mβ∙Tγ , where α, β, γ are exponents which in general can be positive, negative, zero, integer or not.
