# The Naked Scientists Forum

### Author Topic: Who wants to learn a new conservation law?  (Read 17602 times)

#### jartza

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##### Who wants to learn a new conservation law?
« on: 11/11/2010 05:00:04 »

If we have some mass in a closed box, it is not possible to the inertia of the box to change, also the weight of the box can not change. In other words inertial mass and gravitational mass are conserved. In other words mass is conserved.

(this "closed box" here is a "closed system", so it's much more closed than for example a closed safe )

Now that we know that mass is conserved, we know that mass does not change into energy, and energy does not
change into mass. We know that people who talk about mass changing into energy are confused, or uneducated, or they just haven't thought about it enough.

#### JP

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##### Who wants to learn a new conservation law?
« Reply #1 on: 11/11/2010 05:17:17 »
Now that we know that mass is conserved. . .

But mass isn't conserved, which is precisely what's being stated when it's said that matter and energy can be changed into one another.  Energy is what is actually conserved.
« Last Edit: 11/11/2010 05:22:10 by JP »

#### namaan

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##### Who wants to learn a new conservation law?
« Reply #2 on: 11/11/2010 06:22:22 »
A new conservation law hmm? Well how about the Law of Conservation of Information. Sounds all scifi and cool at least...I'll let you know if I figure it out ;)

#### pranza

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##### Who wants to learn a new conservation law?
« Reply #3 on: 11/11/2010 06:53:05 »
Energy can only be changed into another state of energy. It can not be created or destroyed.

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #4 on: 11/11/2010 09:56:06 »

But mass isn't conserved, which is precisely what's being stated when it's said that matter and energy can be changed into one another.  Energy is what is actually conserved.

JP, here's an example:

"An object that has a large mass is heavy to lift and difficult to stop when it's moving"

In this sentence the word mass is used correctly. It's correct English and correct physics.

Here's another sentence:

"Mass is conserved"

In this sentence the word mass has the same meaning as in the sentence number 1.

Oh yes and mass is conserved. The mass that I have been explaining here.

Also it's worth mentioning this same mass obeys this equation: E=mc2

(I'm not necessarily absolutely denying other "masses")

#### Bill S

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##### Who wants to learn a new conservation law?
« Reply #5 on: 11/11/2010 12:36:24 »
Quote from: jartza
If we have some mass in a closed box, it is not possible to the inertia of the box to change, also the weight of the box can not change. In other words inertial mass and gravitational mass are conserved. In other words mass is conserved.
If the mass in your box happened to be the lump of uranopilite I picked up in Cornwall some years ago, would that not change the situation?

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #6 on: 11/11/2010 18:00:51 »
If the mass in your box happened to be the lump of uranopilite I picked up in Cornwall some years ago, would that not change the situation?

You asked the right question. No there is no change of mass in a closed box with a lump of radioactive material in it.

Here's one small exercise question:
In a closed box there is a lump of nuclear waste, that is always warm, and a bucket full of cold water. Tell me something about how mass changes place in this box.

#### JP

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##### Who wants to learn a new conservation law?
« Reply #7 on: 12/11/2010 05:17:12 »
Ah... the problem might be in wording.  Conservation of some "stuff" means that if you add up all the stuff before a physical process, and then add it all up after the physical process, you get the same number.  What you're getting at here is that if you fill a box with energy and seal it up, the box acts as if it has mass.

For example, if you have a closed box and fill it with radioactive matter such that no energy can escape from the box, then you can't tell whether it's mass is due to the energy or mass of the radioactive matter.

If you peek inside the box, still without letting any energy leak out, then you can see that the mass of the radioactive material has changed into energy, although the apparent mass of the box itself as viewed from the outside remains the same.  Since mass can be "created" in a sense from energy, and since energy seems to be more fundamental to physical processes, this is usually called conservation of energy, not mass.

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #8 on: 12/11/2010 14:28:28 »
Ah... the problem might be in wording.

Physics says silly things sometimes.

Let's put a small lump of radioactive material into a large box, the lump is put at the middle of the box. Then we put the box at a frictionless surface, and we make the box spin. As we know, the spinning will slow down because of what happens in the box.

Now what words do we use to describe what happens in the box, so that slowing down will be well understood?

#### lightarrow

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##### Who wants to learn a new conservation law?
« Reply #9 on: 12/11/2010 18:07:57 »

Physics says silly things sometimes.

Let's put a small lump of radioactive material into a large box, the lump is put at the middle of the box. Then we put the box at a frictionless surface, and we make the box spin. As we know, the spinning will slow down because of what happens in the box.
Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.

Anyway you are right in pointing out the pitfalls in using the phrase "mass converted into energy". This phrase is reiterated from almost everyone but it's misleading, unless it's specified "mass of what" and "energy of what"; actually energy can shift from a kind, or a location, to another, but there is no conversion at all...
« Last Edit: 12/11/2010 18:19:24 by lightarrow »

#### lightarrow

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##### Who wants to learn a new conservation law?
« Reply #10 on: 12/11/2010 18:23:23 »
Here's one small exercise question:
In a closed box there is a lump of nuclear waste, that is always warm, and a bucket full of cold water. Tell me something about how mass changes place in this box.
Do you mean the fact that the lump's mass decreases while the water's mass increases?

#### Bill S

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##### Who wants to learn a new conservation law?
« Reply #11 on: 12/11/2010 18:52:29 »
Quote from: lightarrow
the water's mass increases

Where did the water come from?

#### Geezer

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##### Who wants to learn a new conservation law?
« Reply #12 on: 12/11/2010 19:56:32 »
This is beginning to sound a lot more like a new theory than an actual question.

#### lightarrow

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##### Who wants to learn a new conservation law?
« Reply #13 on: 12/11/2010 20:20:05 »
Quote from: lightarrow
the water's mass increases

Where did the water come from?
<<In a closed box there is a lump of nuclear waste, that is always warm, and a bucket full of cold water>>.

#### Bill S

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##### Who wants to learn a new conservation law?
« Reply #14 on: 12/11/2010 20:27:45 »
Oops. Forgot the bucket of water. [:I]

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #15 on: 13/11/2010 01:03:04 »
Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.

In physics book there is a formula for moment of inertia, there is a "m" in that formula, the "m" is pronounced "mass".

Quote

Anyway you are right in pointing out the pitfalls in using the phrase "mass converted into energy". This phrase is reiterated from almost everyone but it's misleading, unless it's specified "mass of what" and "energy of what"; actually energy can shift from a kind, or a location, to another, but there is no conversion at all...

It's a big sink hole to say that mass is not conserved. It spoils our moment of inertia formula.

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #16 on: 13/11/2010 01:19:44 »
Do you mean the fact that the lump's mass decreases while the water's mass increases?

Yes I do mean that.
There are two recoils too. One when something starts to move, another when aforementioned motion stops. This "something" is energy.

But saying "there's a recoil when mass starts to move" is actually better way to say it, isn't it?

#### lightarrow

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##### Who wants to learn a new conservation law?
« Reply #17 on: 13/11/2010 15:10:39 »
Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.

In physics book there is a formula for moment of inertia, there is a "m" in that formula, the "m" is pronounced "mass".
And? I don't grasp the problem.

#### lightarrow

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##### Who wants to learn a new conservation law?
« Reply #18 on: 13/11/2010 15:14:04 »
Yes I do mean that.
There are two recoils too. One when something starts to move, another when aforementioned motion stops. This "something" is energy.

But saying "there's a recoil when mass starts to move" is actually better way to say it, isn't it?
I don't say that, because there is recoil even when you shoot a laser beam, or energy, in general, as you wrote. What is that you really want to say?

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #19 on: 13/11/2010 22:14:45 »
Are you talking about the increase of the moment of inertia of the system because some matter in the centre went out of it? That is the way I would describe it.

In physics book there is a formula for moment of inertia, there is a "m" in that formula, the "m" is pronounced "mass".
And? I don't grasp the problem.

Do you grasp the benefit? There is a formula for moment of inertia of a homogeneous cube.
The cube may be a matter cube. Or it may be an energy cube. When mass is evenly spread in the cube the formula works.

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #20 on: 13/11/2010 23:20:50 »
What is that you really want to say?

Do you grasp the law of conservation of mass?

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #21 on: 14/11/2010 04:30:46 »
Maybe it would be polite to pay some attention to the misguided point of views too.

These are JP's views:
Energy is more fundamental than mass, energy does not have mass, energy kind of "creates" mass, mass turns into energy.

Well, I have heard that mass and energy are equivalent.

This is from lightarrow:
It is not OK to say mass turns into energy, it is OK to say mass of a potato turns into energy.

Well, sounds to me the same thing is said, the last one is just more specific.

#### JP

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##### Who wants to learn a new conservation law?
« Reply #22 on: 14/11/2010 06:55:53 »
I think we can safely say this has strayed into New Theories territory...

#### simplified

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##### Who wants to learn a new conservation law?
« Reply #23 on: 14/11/2010 10:29:59 »
Nearby  Sirius B a photon is approaching to it, this photon is receiving energy. Is this event reducing mass of Sirius B?

#### jartza

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##### Who wants to learn a new conservation law?
« Reply #24 on: 14/11/2010 11:08:41 »
I think we can safely say this has strayed into New Theories territory...

Are you going to elaborate on mass-energy relationship?
That's what I expected next in this discussion.

#### The Naked Scientists Forum

##### Who wants to learn a new conservation law?
« Reply #24 on: 14/11/2010 11:08:41 »