# The Naked Scientists Forum

### Author Topic: Are we seeing energy changing into matter on Earth?  (Read 21649 times)

#### yor_on

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##### Are we seeing energy changing into matter on Earth?
« Reply #25 on: 06/01/2009 18:23:23 »
Thanks Lightarrow.
I will ask you more things, I'm sure.
But first I will need to assimilate what you already shown me.

Considering the average density of my head.
Quite thick I'm afraid.
It will take me some time:)

But, as they say in sunny California...
"I'll be back"

--------Quote-------

They are different concepts, even because they have different units and one is a scalar while the other is a (pseudo) vector.
Given a system of N particles, you have:

Angular momentum (pseudo vector) = K = ∑i ri Λ mivi          units: Joule*second
ri = position vector of the i-esim particle
mi = mass of the i-esim particle
vi  = velocity of the i-esim particle
Λ = vectorial product

Rotational kinetic energy (scalar) = Er = ∑i (1/2)mi(viG)2         units: Joule
where viG is the velocity of the i-esim particle with respect to the centre of mass G. For a rigid body such velocities viG are all perpendicular to the vector radius from the axis of rotation; for this reason it could be demonstrated that
Er = (1/2)Iω2

--------------------End - Quote --

Yes, I can see that one is scalar and that the other describing the whole 'system / coin' of scalar 'bonds' will be seen as a vector (magnitude and direction)

Is there anywhere one can download the most common expressions of 'symbolic' expressions and their definitions?
Or do they change depending on what you use them for?

Often when I see those mathematical symbolic formulas they don't get explained.
And sometimes they don't seem to be bound to any 'definite description'

So doing like you do makes me want to put numbers into your formulas to see if I really understands them.
And that's why I will need to go slow.
This is a new language for me.

I've done some boolean logic, Computers and Philosophy, but that is the nearest I've ever cometh :)
So I do enjoy the care you take in explaining your concepts and math here.

Cheers.
yoron.

« Last Edit: 06/01/2009 18:52:55 by yor_on »

#### lightarrow

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##### Are we seeing energy changing into matter on Earth?
« Reply #26 on: 07/01/2009 11:05:34 »
http://theory.uwinnipeg.ca/physics/rot/node6.html

About vectorial product, the rule is the following. Given the two vectors:

A = (Ax,Ay,Az)

B = (Bx,By,Bz)

then:

AΛB = (AyBz-AzBy,AzBx-AxBz,AxBy-AyBx)
« Last Edit: 07/01/2009 15:06:57 by lightarrow »

#### yor_on

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##### Are we seeing energy changing into matter on Earth?
« Reply #27 on: 07/01/2009 12:12:06 »
What?

Only joking:)

Thanks..
And I'm goggling.
Or should it be ogling?

:)

#### lightarrow

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##### Are we seeing energy changing into matter on Earth?
« Reply #28 on: 07/01/2009 15:12:43 »
What?

Only joking:)

Thanks..
And I'm goggling.
Or should it be ogling?

:)

Actually, there is a little picture which helps remembering that rule: write the symbols x, y, z in this order, clockwise in a circle. So you understand that the x component of the vectorial product is given by the product of the y component of the first vector by the z one of the second (from y to z you go clockwise) minus the z component of the first by the y one of the second (because now you go anti-clockwise): AyBz-AzBy.
The same rule for the other components.
« Last Edit: 07/01/2009 15:23:30 by lightarrow »

#### yor_on

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##### Are we seeing energy changing into matter on Earth?
« Reply #29 on: 08/01/2009 15:43:16 »
Ahem, perfectly understandable.
With some thought?
perhaps?

And yes, we are talking density here.
(between my ears:)

-----

The first one was easier on my mind than this second ::))
But that may have to do with my English?

There is only one conclusion can I draw after reading your explanation over, some times.
You are right no matter what sense I will make.

I will never forget that little picture:)
« Last Edit: 08/01/2009 16:58:20 by yor_on »

#### The Naked Scientists Forum

##### Are we seeing energy changing into matter on Earth?
« Reply #29 on: 08/01/2009 15:43:16 »