Various Laws in engineering etc

[tim west]

I'll have you know it has sound engineeering reasoning behind it

 

[Softus]

The moment of a force
is the product of the force
and its perpendicular distance from the pivot.

 

[WDIK]

Hmm Im sure the term i was taught in 1st yr physics was not pivot but fulcrum.

 

[WDIK]

an often debated point.

The law of conservation of mass/matter, also known as law of mass/matter conservation (or the Lomonosov-Lavoisier law), states that the mass of a closed system will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter cannot be created/destroyed, although it may be rearranged. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products.

The law of "matter" conservation (in the sense of conservation of particles) may be considered as an approximate physical law that holds only in the classical sense before the advent of special relativity and quantum mechanics. Mass is also not generally conserved in open systems, when various forms of energy are allowed into, or out of, the system. However, the law of mass conservation for closed systems, as viewed from their center of momentum inertial frames, continues to hold in modern physics.

 

[Ricky2]

an often debated point.

The law of conservation of mass/matter, also known as law of mass/matter conservation (or the Lomonosov-Lavoisier law), states that the mass of a closed system will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter cannot be created/destroyed, although it may be rearranged. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products.

The law of "matter" conservation (in the sense of conservation of particles) may be considered as an approximate physical law that holds only in the classical sense before the advent of special relativity and quantum mechanics. Mass is also not generally conserved in open systems, when various forms of energy are allowed into, or out of, the system. However, the law of mass conservation for closed systems, as viewed from their center of momentum inertial frames, continues to hold in modern physics.

Couldn't have put it better myself WDIK

 

[Softus]

Couldn't have put it better myself WDIK

You've misspelt the word "Wiki" there.

View media item 783
See http://en.wikipedia.org/wiki/Conservation_of_mass for more details.

Naturally, copyright applies to Wikipedia content, as follows:

The license Wikipedia uses grants free access to our content in the same sense as free software is licensed freely. This principle is known as copyleft. That is to say, Wikipedia content can be copied, modified, and redistributed so long as the new version grants the same freedoms to others and acknowledges the authors of the Wikipedia article used (a direct link back to the article satisfies our author credit requirement). Wikipedia articles therefore will remain free under the GFDL and can be used by anybody subject to certain restrictions, most of which serve to ensure that freedom.

 

[robertito]

So it's a slap on the wrist for WDIK then....

 

[Softus]

So it's a slap on the wrist for WDIK then....

Is that the punishment for the criminal act of breaking copyright law?

 

[robertito]

No, not really, my mistake....

 

[Softus]

No worries, robertito. Welcome to the forum.

 

[Space cat]

However, the law of mass conservation for closed systems, as viewed from their center of momentum inertial frames, continues to hold in modern physics.

That has some interesting implications. Consider a closed system containing electrons and positrons in equal numbers. The mass inside this system can be measured from outside in two ways: inertia and gravity.

Now let the those particles do their stuff and recombine into pure energy. If the mass inside the closed system is conserved, does this imply that photons have mass? I can just about see how the closed system will still possess inertia because the photons are bouncing around inside. As they bounce off a moving wall they will change frequency, and hence also momentum. But what happens to gravity?

 

[tim west]

But what happens to gravity?

That's easy! It continues to make the apples in the closed system fall.

 

[Space cat]

It continues to make the apples in the closed system fall.

It's not that simple. When the closed system was filled with massive particles it had a gravitational field that extended outside and made apples fall towards it. The question is this: When the particles have all gone and the closed system contains pure energy, do the apples still fall towards it?

If they do then the implication is that massless photons still have gravity. Can anybody confirm or deny this? The alternative is even stranger. I don't think there is any proof that inertia and gravity really have the same origin, ie mass. It is assumed that they do because all our experiments point that way but that's not proof. If the mass inside the closed system really is conserved while its gravitational field vanishes, that would be proof that they have different origins. That is to say that inertial mass is not the same as gravitational mass.

 

[WDIK]

Couldn't have put it better myself WDIK

not my work at all, sorry forgot to put it in quotes,
but if it wound someone (singular) up then it wasnt wasted

 

[Adam_151]

If they do then the implication is that massless photons still have gravity. Can anybody confirm or deny this? The alternative is even stranger.

Does anything count as strange where sub atomic particles are involved?

[there are no points, btw for saying strange quarks ]