# The Naked Scientists Forum

### Author Topic: Signs.  (Read 4161 times)

#### Quantum_Vaccuum

• Sr. Member
• Posts: 135
• The Base Of Chemistry
##### Signs.
« on: 09/10/2007 01:48:50 »
What do each of these mean? (Yes im only a young teenager!)

Σ:
Ψ:
Φ:
Ω: Omega right?
Δ: Delta, change over...
α: Gama?
β:
γ:
δ:
ε:
ζ:
η:
θ:
λ:
μ:
ξ:
π: this looked like pi when i posted it...
ρ:
ς:
σ:
φ:
ψ:
ω:
∞: Infinity
∂:

#### another_someone

• Guest
##### Signs.
« Reply #1 on: 09/10/2007 03:27:22 »
Apart from the last three, they are all letters of the Greek alphabet, but commonly used in mathematics.

http://en.wikipedia.org/wiki/Greek_alphabet
Quote
 Α α Alpha Ν ν Nu Β β Beta Ξ ξ Xi Γ γ Gamma Ο ο Omicron Δ δ Delta Π π Pi Ε ε Epsilon Ρ ρ Rho Ζ ζ Zeta Σ σ Sigma Η η Eta Τ τ Tau Θ θ Theta Υ υ Upsilon Ι ι Iota Φ φ Phi Κ κ Kappa Χ χ Chi Λ λ Lambda Ψ ψ Psi Μ μ Mu Ω ω Omega

Upper case sigma is used for summation - for instance:

i=5
Σ i2
i=1

means sum the squares of the numbers 1 to 5.

Upper case delta, as you surmise, is used for finite differences.

Many of the symbols have multiple meanings, depending on the branch of science or mathematics you are working in.  You might want to follow the links for each greek letter, and it will show all the different contexts in which the letter has one or other meaning.

Even upper case pi can be used for a series product in the same way the upper case sigma can be used for series summation.

For a list of mathematical you can look at http://en.wikipedia.org/wiki/Mathematical_symbols
« Last Edit: 09/10/2007 03:46:45 by another_someone »

#### Quantum_Vaccuum

• Sr. Member
• Posts: 135
• The Base Of Chemistry
##### Signs.
« Reply #2 on: 09/10/2007 03:46:23 »
And what do they exactly mean?

that is like the names, but what are each of them?

#### another_someone

• Guest
##### Signs.
« Reply #3 on: 09/10/2007 04:12:40 »
And what do they exactly mean?

that is like the names, but what are each of them?

As I said, none of them have a single meaning, but some of them have meanings by which they are more commonly known.

For instance, in mathematics, lower case alpha, beta, and theta, are often used to denote angles.  On the other hand, alpha and beta and gamma, in nuclear physics, are types of radiation, and the lower case Greek symbols are often used to denote that, and lower case alpha is also used to represent the fine-structure constant.

Lower case lambda is often used to denote a function.

Rho is used as a measure of electrical resistivity, or of density.

Omega is used to denote ohms, a measure of electrical resistance (rho is used to denote the variable of which the ohms is the unit of measure).

Lower case mu is most commonly used as a prefix meaning 'micro', or one millionth of (e.g. μW would mean a microwatt, or a millionth of a watt).  On the other hand, the same symbol is used to refer to the coefficient of friction, or in nuclear physics it may refer to a muon, and has numerous other meanings also.

#### Quantum_Vaccuum

• Sr. Member
• Posts: 135
• The Base Of Chemistry
##### Signs.
« Reply #4 on: 09/10/2007 04:20:48 »
but i've always seen: Σ(Singma) in scinece, whats that one mean?

#### another_someone

• Guest
##### Signs.
« Reply #5 on: 09/10/2007 04:44:26 »
but i've always seen: Σ(Singma) in scinece, whats that one mean?

http://en.wikipedia.org/wiki/Sigma#Science_and_Mathematics
Quote
Upper case Σ is used as a symbol for:

• the summation operator
• a class of baryons in particle physics
• macroscopic cross sections in nuclear and particle physics
• in economics this letter is for the balance of the invoice classes, the overall amount of the depts and demands

#### lightarrow

• Neilep Level Member
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##### Signs.
« Reply #6 on: 09/10/2007 20:39:14 »
In addition to what another_someone said, something that comes to my mind (so I will certainly forget many):

Ψ: usually used for "wavefunction" in quantum mechanics.
γ: sometimes used for a viscous coefficient in differential equations, or to mean photons in QM or particle physics.
δ: sometimes used for density or for a small variation of a function (usually a specific kind of variation, such those made in lagrangian mechanics), or for a virtual dispacement in mechanics, or for angles.
ε: usually used for electric permittivity in electrodynamics (ED) or for very little values in mathematics.
ζ: for ζ Riemann function in mathematics or as "z" coordinate in another frame of reference (from (x,y,z) to (ξ,η,ζ), for example).
η: usually used for viscosity.
λ: usually used for wavelenght.
μ: usually used for magnetic permittivity in ED and sometimes used for reduced mass in mechanics.
σ: Pauli's matrices in QM, conductivity in ED, areas.
ω: angle's velocity.
∂: partial derivative.

#### Bored chemist

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##### Signs.
« Reply #7 on: 10/10/2007 19:34:06 »
"And what do they exactly mean?

that is like the names, but what are each of them?"
Well most of them are letters of the alphabet. Not the Roman one that most of use use most of the time, but the Greek alphabet.
My Greek is pretty near non-existant so I hope those who know better will forgive me for any mistakes but, for the most part the character "µ" is the Greek equivalent of our "m"; π corresponds to "p".

In the same way that we often use letters to designate thing because it's easier than writing them out in full people often use Greek letters- because they are Greek they don't usually get muddled up with the rest of the text.

Unfortunately, there is no universally agreed use for them  (as was pointed out, even pi has at least 2 common uses in maths and another in chemistry).
If this were not confusing enough I guess we could start using cyrillic letters and the Jewish alphabet too.
Even then we would still have a few more symbols . That  ∂ is just a funny looking d as far as I know.
« Last Edit: 10/10/2007 19:36:36 by Bored chemist »

#### another_someone

• Guest
##### Signs.
« Reply #8 on: 10/10/2007 21:37:30 »
There is no Jewish alphabet, but there is a Hebrew alphabet, and it is already used to designate Aleph numbers used in set theory.

#### DoctorBeaver

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##### Signs.
« Reply #9 on: 10/10/2007 21:52:11 »
Ψ: is also shorthand for psychology.

#### The Naked Scientists Forum

##### Signs.
« Reply #9 on: 10/10/2007 21:52:11 »