Re: one question

```To: Steve and Kevin

>For much the same reasons that I don't like "relativistic mass",
>I don't like the notion of imparting momentum to a non-moving
>object.  Clearly it has lead to some incorrect physical
>thinking.  If something can't be put into uniform linear motion
>relative to something else, then it can't "absorb momentum"
>relative to that thing.

While for relativistic mass there is just a different word for the same
thing, there is in this case no other word.
The word that here is invented is "imparted momentum" which should replaced
by the word "energy".

Timothy

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Subject: Physics store

>Others have given you the address of the Acme Physics Warehouse.
>The stuff you want is probably in the "Cartoon Physics" section;
>the "Real Physics" section just has stuff like point masses,
>frictionless surface coatings, and ideal gases.

I'm not sure, that unobtanium with its negative mass seemed to come from the
same store. But if you are right, then that Wile guy has lied to me and
probably is on the run with my down payment. :(

>You can do antigravity in several ways.  One is to keep a
>suspended creature permanently in ignorance of its altitude with
>special blinders; as you know, creatures won't fall until they
>know they are above a canyon.  Another is to surprise a creature,
>causing it to levitate above the ground, then keep it in that
>state; you can get boxes of carefully bred mice that are easily
>surprised.  Someone in love will float above the ground, and can
>be tugged around simply by the scent of the loved one, implying
>minimal inertia; tailored "love drugs" can be used to induce this
>state.

All these examples seem to have some mental control mechanism. That probably
means that I have to do a lot of yoga lessons first.

Timothy

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To: Steve

>There is one important constraint in this situation:  photons
>_always_ have equal momentum and energy; hence a photon
>reflecting off a moving object must impart equal amounts of
>momentum and energy to it.

Yes, I was aware of that: U = p c

>A photon has less energy when seen from the frame of a
>fast-moving object moving in the same direction as the photon, so
>in the object frame the photon imparts less momentum to the
>object.  Seen from the observer's frame, the photon loses more
>momentum to a receding fast-moving object than a slow-moving one.

Indeed, that would make it right in all frames.

>Remember that reflecting objects moving opposite to the direction
>of the incident photons actually impart energy and momentum to
>the photons; in the object frame the photon has more energy and
>momentum.

Yes, because the moving observer would see a higher energy than an observer
at rest.

> > After all this, can we conclude a charged battery is heavier than an
> > uncharged battery?
>
>Yes, this is also true.  Hot objects are heavier than cold ones
>(although not by an amount we have equipment to measure).  A
>mirrored box full of photons is heavier than the empty box.

And it doesn't matter if they all move parallel and in the same direction
all the time, right?

Here is another one: If two particles feel the gravity of each other, then
they are heavier together than if they are separate because of the extra
gravitational energy.

> > Yes, in fact is does not take any energy to keep floating a few metres above
> > Earth's surface.
>
>Well, it depends on how you make the object float.

No, if you for example use a helicopter, it does not take energy to stay at
that height but it does take energy to move all the air.

A true anti-gravity source would only have to build up a anti-gravity field
once and does not use energy to stay at a certain heigh.

If you use two magnets or two charged plates (both positive or negative)
they also would not use any energy after you levitated.

Timothy

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