# Weird Physics Symbols

Is there a reference list anywhere where I can look for the meaning of a weird physics symbol when I run across one? For instance there is a thing that looks like a sideways capitol M. (There are two of them in the new PF banner to the right of Einstein's face.)

I ran into this sideways capitol M in one version of Hookes law:

(Weird Sideways Capitol M)F = -kx

A different physics text gave Hookes law as F~(triangle)x

The triangle, I believe, is delta, which means change, but I'm not sure what the ~ means.

In both cases I understood the verbal explanations of Hookes law, which is that the restoring force is directly proportional to the amount of displacement from equilibrium.

The meaning of the symbols I don't understand is, no doubt, covered in earlier chapters I haven't read. However I often look things up as background for something else I'm researching and don't have time to read the previous 300 pages to find the symbol that is baffling me. Therefore if anyone has a link to a list of these symbols and what they mean it would be a great help.

Zoobyshoe

## Answers and Replies

Integral
Staff Emeritus
Science Advisor
Gold Member
Is this

$$\Sigma$$
The weird sideways M?

If so that is a Greek Sigma, it is used to denote summation. In your case it would be the Sum of the Forces.

chroot
Staff Emeritus
Science Advisor
Gold Member
The tilde, in that context, is used to indicate proportionality: F is proportional to the change in x.

It's most often shown as

$$F \propto \Delta x$$

and is read as "F is proportional to the change in x."

- Warren

$$\Sigma$$

Yes this is it.

I don't understand why they would express Force that way in Hooke's law.

Why "the sum of the forces" rather than just "force"? I think there is only one force at work here (simple harmonic motion): the restoring force.

chroot said:
It's most often shown as

$$F \propto \Delta x$$

and is read as "F is proportional to the change in x."

So that one is called "propto", I see from the LaTeX and means "is proportional to", and is the same as the tilde ~.

No list of these symbols anywhere?

chroot
Staff Emeritus
Science Advisor
Gold Member
zooby,

It's a stupid notation in the case of Hooke's law. F is always considered to be the net force, and that's all $\Sigma F$ means -- net force.

There is no specific list of symbols anywhere, because often the symbols are dependent on context. There are many different ways or representing the same equation, with different notational systems. Unfortunately, since there is no rigorous standard, there can be no cheat-sheet.

- Warren

chroot said:
zooby,

It's a stupid notation in the case of Hooke's law. F is always considered to be the net force, and that's all $\Sigma F$ means -- net force.
That's good to know. I'm glad to know it's stupid because I thought the other one was much easier to understand.
There is no specific list of symbols anywhere, because often the symbols are dependent on context. There are many different ways or representing the same equation, with different notational systems. Unfortunately, since there is no rigorous standard, there can be no cheat-sheet.
Bummer. I've always been hesitant to ask what they mean because I don't even know what they're called when the text doesn't refer to them by name. Like with "propto" I'd have to ask:"What does a sideways 8 with the right half of the right loop cut off mean?".

chroot
Staff Emeritus
Science Advisor
Gold Member
I feel your pain -- you have an excellent resource right here at pf though. Ask anything you'd like.

- Warren

robphy
Science Advisor
Homework Helper
Gold Member
Last edited by a moderator:
chroot said:
you have an excellent resource right here at pf though.
This is true. Thanks Warren and Integral.

One thing I'd like to note here is about the symbol: ∝ (Greek: alpha)

This is used in mathematical functions as proportional as stated in the example you've given yet there are other uses for Greek alpha as angular acceleration, linear expansion, coefficients (sometimes), and alpha particles.

It is a wonder we get anything scientifically done at all with the complete lack of standardized symbols and communication without reference.

Cheers,
Matthew Jordan