1.2 Physical Quantities
In the development of physics it turned
out again and again how
diﬃcult, but also impor-
tant it was to
develop the most
suitable concepts and
ﬁnd the relevant
quantities (e.g.
force or energy)
in terms of
which nature can
be described both
simply and comprehen-
sively.
Insert: History: It
took more than
100 years for
the discussion among
the “nat-
ural philosophers” (especially
D´Alembert, Bruno, Newton,
Leibniz, Boskovic and
Kant) to create
our modern concepts
of force and
action from the
old terms prin-
cipium, substantia, materia,
causa eﬃciente,
causa formale, causa
ﬁnale, eﬀectum,
actio, vis viva
and vis insita.
Every physical
quantity consists
of a a measured
value and a
measuring unit,
i.e.
a pure number
and a dimension.
All diﬃculties in
conversations are avoided,
if we treat
both parts like
a product “value
times dimension”.
Example: Velocity: In
residential districts often a speed limit v
= 30
km
h
is imposed, which
means 30 kilometers
per hour. How
many meters is
that per second?
One kilometer contains
1000 meters: 1km
= 1000m,
thus v
= 30 ·
1000
m
h
.
Every hour consists
of 60 minutes:
1h = 60min,
consequently v
= 30 ·
1000
m
60min
.
One minute has
60 seconds: 1
min = 60
s , therefore
v = 30
·1000
m
60·60s
= 8.33
m
s
.
Even that may
be too fast
for a ball
playing child.
Insert: Denotations: It
is an accepted
thing in international
physics for long
time past to
abbreviate as many
of the physical
quantities as possible
by the ﬁrst
letter of the
corresponding English
word, e.g. s(pace),
t(ime), m(ass), v(elocity),
a(cceleration), F(orce), E(nergy),
p(ressure), R(esistance),
C(apacity), V(oltage),
T(emperature), etc..
Of course there
are some exceptions
from this rule:
e.g. momentum p,
angular
momentum l, electric
current I or
potential V
Whenever the Latin
alphabet is not
suﬃcient, we use
the Greek
one:
alpha α
A
beta β
B
gamma γ
Γ
delta δ
∆
epsilon
E
zeta ζ
Z
eta η
H
theta θ
Θ
iota ι
I
kappa κ
K
lambda λ
Λ
my µ M
ny ν
N
xi ξ
Ξ
omikron o
O
pi π
Π
rho ρ
P
sigma σ
Σ
tau τ
T
ypsilon υ
Y
phi φ
Φ
chi χ
X
psi ψ
Ψ
omega ω
Ω
In addition the
Gothic alphabet is
at our disposal.
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