# What is a moment?

1. Apr 15, 2007

### Mathgician

Don't flame me please What is a moment? I learn it in math and in physics , I never really got either enough experience in it or never came to a realization.

2. Apr 16, 2007

### Cyrus

Its a twisting tendency that occurs when you have a force applied at some distance from an axis of rotation.

3. Apr 16, 2007

### christianjb

There's at least one other common usage of the word moment
the nth moment of a distribution is defined as

$\int \rho(x) x^n dx$

4. Apr 16, 2007

### Mathgician

so why is this word used in such general terms? Is magnetic moment same as mechanical moment in classical mechanics in general?

5. Apr 16, 2007

### christianjb

I'll tell you in just a moment....

I think almost all use of the term 'moment' is related to some sort of integral like the one in my post. You'd have to study the equations to see if this is true.

6. Apr 16, 2007

### Cyrus

Yes, a moment is a moment is a moment.

7. Apr 16, 2007

### lpfr

There are several "moments" in physics. When a physicist does not how to name a physical quantity, he christens it "moment something". There are (at least):
linear moment
angular moment
moment of a force
moment of inertia
dipole moments (magnetic and electric)

cyrusabdollahi described the moment of a force.
I think that the one you are asking is the linear moment. This is the product of the mass of the object times its speed. p = mv.
When you are hit by a moving object (I do not talk about hurting or killing hits!) it is the moment of the object that will overthrow you or not. Not the speed or the mass alone, but the product of both.
For the other moments you can begin reading the corresponding entry in wikipedia and post your questions if there is still something unclear.

8. Apr 16, 2007

### christianjb

Physicists can also be a 'she'.

9. Apr 16, 2007

### Mathgician

:rofl: :rofl: :rofl: :rofl: :rofl:

Thanks lpfr, I think your explaination was what I was seeking, anyone elese have any other insights I would appreciated very much. Funny Christianjb, very funny. Do you mind If I ask you what your gender is?

Last edited: Apr 16, 2007
10. Apr 16, 2007

### cristo

Staff Emeritus
I think here you mean "linear momentum" and "angular momentum." You have then gone on to give a description of linear momentum, when the OP asks "what is moment;" not "what is momentum."

11. Apr 16, 2007

### Mathgician

Yeah p or mv is momentum, not moment

12. Apr 16, 2007

### christianjb

I'm male, but I know some excellent female physicists.