From Newsgroup: sci.physics

On 1/6/2026 1:57 PM, Paul.B.Andersen wrote:

Den 06.01.2026 09:15, skrev Thomas Heger:

Am Sonntag000004, 04.01.2026 um 20:51 schrieb Paul.B.Andersen:

E = mc² is the energy content, or the energy equivalent of
the mass m. Mass is invariant, so this equation is valid for
all speeds of the mass.

You contradicted yourself!!

Here your claim is, that mass is invariant, while a little below you
claim, that energy is conserved, while mass has vanished from a
radioactive sample.

But you can't keep both claims, because they contradict each other.

Invariant means "the same in all frames of reference"
or "independent of speed".

It does _not_ mean "constant".

Mass is invariant.
The mass of an object is the same in all frames of reference.
The mass of an object does not depend on the speed of the object.

But mass can change. Heat the object, and its mass will increase,

I have told you before, but I know you will not learn.
You never do.

Its odd to think of a cup of water as the water evaporates. The cup is
an object with its own mass. But, now its holding water. So, the cup
"weighs" more in a sense... But, as the water evaporates, that weight
will go back to the weight of the original cup...

Think of two equal mass cups on a scale. They balance. Add water to one,
its not balanced. However, the water will evaporate and the scale shall
go back to balanced over time?
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From Newsgroup: sci.physics

On 1/7/2026 1:20 PM, Chris M. Thomasson wrote:

On 1/6/2026 1:57 PM, Paul.B.Andersen wrote:

Den 06.01.2026 09:15, skrev Thomas Heger:

Am Sonntag000004, 04.01.2026 um 20:51 schrieb Paul.B.Andersen:

E = mc² is the energy content, or the energy equivalent of
the mass m. Mass is invariant, so this equation is valid for
all speeds of the mass.

You contradicted yourself!!

Here your claim is, that mass is invariant, while a little below you
claim, that energy is conserved, while mass has vanished from a
radioactive sample.

But you can't keep both claims, because they contradict each other.

Invariant means "the same in all frames of reference"
or "independent of speed".

It does _not_ mean "constant".

Mass is invariant.
The mass of an object is the same in all frames of reference.
The mass of an object does not depend on the speed of the object.

But mass can change. Heat the object, and its mass will increase,

I have told you before, but I know you will not learn.
You never do.

Its odd to think of a cup of water as the water evaporates. The cup is
an object with its own mass. But, now its holding water. So, the cup "weighs" more in a sense... But, as the water evaporates, that weight
will go back to the weight of the original cup...

Think of two equal mass cups on a scale. They balance. Add water to one,
its not balanced. However, the water will evaporate and the scale shall
go back to balanced over time?

LOL! Think if the cups were made of paper. The water itself might break
down the cup and parts of the cup would wash away...
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From Newsgroup: sci.physics

Chris M. Thomasson wrote to sci.physics.relativity and sci.physics:

Its odd to think of a cup of water as the water evaporates. The cup is
an object with its own mass. But, now its holding water. So, the cup "weighs" more in a sense...

The mass of the cup only has increased because when we say "cup" now we mean the substance of the cup *and* the water.

But, as the water evaporates, that weight will go back to the weight of
the original cup...

That is only true if the water actually leaves the cup. Put a lid on the
cup so that the water cannot escape, and the mass of the water-filled cup
will not decrease.

But, more relevant to this discussion, by increasing the rest energy of the water(-filled cup) by increasing the kinetic energy of the water molecules
(and to some extent the substance of the cup, too) by heating the
water(-filled cup), the mass of the water(-filled cup) increases slightly (probably unmeasurably, given m = E_0/c^2).

See also the videos that I referred to in <mid:10j721n$1i2q$1@gwaiyur.mb-net.net>.

Think of two equal mass cups on a scale. They balance. Add water to one,
its not balanced. However, the water will evaporate and the scale shall
go back to balanced over time?

If the water *leaves* the cup, yes.

Notice also that what you are measuring there is weight, not mass. That is, this is only an indirect determination of mass that depends on gravitation, therefore the assumption of a uniform gravitational field (which we know is
not so, but just a relatively good approximation near the surface).

F'up2 sci.physics.relativity
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