relative mass

[sidharath]

certain mass is attached to stationary spring balance, next the spring balance is subjected to very high upward velocity Will the spring balance show high reading due to increase in relative mass as a result of high velocity ?

[Strange]

This doesn't increase the mass of the object, just its apparent weight (due to acceleration).

 

Note that the spring balance will only show an increased weight while it is accelerating; once the system reaches a constant velocity the weight will return to that measured at rest. Because, as we all know, there is no difference between being "at rest" and in a state of steady (inertial) motion.

[Enthalpy]

Maybe Sidarath means the relativistic correction, and then, yes, the scales show an increased weight at constant speed.

 

The chosen case is difficult to observe because a high speed needs a big acceleration over a long path. Easier to observe is the kinetic energy of electrons in heavy atoms: this kinetic energy contributes to the atom's mass and weight, and is observable.

[Strange]

Maybe Sidarath means the relativistic correction, and then, yes, the scales show an increased weight at constant speed.

 

Er, no. That can't be right. Otherwise you could use that measurement to determine your speed. And speed can only be measured relative to something else.

[Ophiolite]

Sometimes I wish I was as clever as I think I am.

[Enthalpy]

 

Er, no. That can't be right. Otherwise you could use that measurement to determine your speed. And speed can only be measured relative to something else.

 

Could you detail that?

 

Presently I believe that rest mass plus kinetic enegy (plus other energies) define an object's inertia, which cannot differ from its gravitational mass. Arguments in messages 10 and 15 there

http://www.scienceforums.net/topic/74526-q-on-general-relativity/

 

How would you enable one to determine an absolute speed through the gravitation created by the kinetic energy? He observes that an object moving with respect to him creates a gravitation field stronger that the rest mass would. I don't see an absolute origin of speed there.

 

In case I was misunderstood: I mean that the moving object produces a stronger gravitational field as experienced by the observer how notices a speed. In the original example, the test mass and the scales move relative to Earth, so Earth produces a stronger gravitational field, and the scales indicate a bigger weight.

Edited August 27, 2014 by Enthalpy

[Strange]

The question was about what happens in the frame of reference of the spring balance and the mass. In this context, there is no change in mass and thus no change in the measured weight (at constant velocity).

 

Someone observing the box containing the spring and mass whizzing past, could observe an increase in relativistic mass of the object, because of its kinetic energy. But this doesn't affect the spring balance, which measure rest mass.

 

This is the same as the question as to whether an object moving near the speed of light will gain enough mass to become a black hole: the answer is no, because again this depends on the rest mass. This is one reason why many people avoid the concept of relativistic mass; it can just confuse people.

 

As to the gravitational effects of the relativistic mass of a fast-moving object: that is actually very complex because the equations of GR don't just use mass and energy, but also momentum, pressure, energy flow ... the closest I have heard from people who could do the math is that it would be hard to work out but it might all cancel out. But the two objects would be so far apart in a short time that it becomes irrelevant anyway.

[Enthalpy]

In the frame of refernce of the scales and mass, Earth is heavier because of its speed.

 

And yes, I believe that rest mass and energy create gravitation, so that the moving Earth attracts the test mass more strongly. This includes kinetic energy, as already discussed there

http://www.scienceforums.net/topic/74526-q-on-general-relativity/

 

Will you suppose that the aluminium tank takes a different orbit aroud the Earth than the carbon+hydrogen fuel it contains? These atoms have a rest mass consisting of varied proportions of kinetic energy at their electrons, which changes the atom's inertial mass.

[Strange]

In the frame of refernce of the scales and mass, Earth is heavier because of its speed..

 

True. But it is also rapidly disappearing!

 

And yes, I believe that rest mass and energy create gravitation, so that the moving Earth attracts the test mass more strongly. This includes kinetic energy, as already discussed there

http://www.scienceforums.net/topic/74526-q-on-general-relativity/

 

 

That thread confirms what I thought: relativistic mass does not increase gravitation (see post #6 for example).

[MigL]

You cannot have different results in different frames.

I could be moving at near light speed right now with respect to some distant galaxy but my scale will still show the same result.

[Sensei]

 

That thread confirms what I thought: relativistic mass does not increase gravitation (see post #6 for example).

 

Counter-argument is in results from particle accelerators:

 

Relativistic proton hitting another proton is creating yet another pair of proton and antiproton.

 

p+ + p+ -> p+ + p+ + p+ + p-

 

From kinetic energy of particle, two new particles are created.

 

Negative mass is not existing, antiproton doesn't cancel proton's mass!

Edited August 28, 2014 by Sensei

[Strange]

 

Counter-argument is in results from particle accelerators:

 

Relativistic proton hitting another proton is creating yet another pair of proton and antiproton.

 

p+ + p+ -> p+ + p+ + p+ + p-

 

From kinetic energy of particle, two new particles are created.

 

Negative mass is not existing, antiproton doesn't cancel proton's mass!

 

I am not disagreeing with that. Energy is clearly equivalent to mass. But linear velocity does not simply add gravitation in the same way.

[Sensei]

Suppose so we have black hole and two protons, one with relativistic velocity, second one with a few km/s.

After dragging them to inside of hole - they're increasing in both cases mass of dark hole by 1.67*10^-27 kg? or by total energy.. ?

 

I am for total energy..

 

[Strange]

I am for total energy..

 

Yes.

[MigL]

Well, let's see. A black hole conserves mass ( or energy ), charge AND angular momentum.

If a massive star is moving as it collapses to a BH,it must also conserve linear momentum.

If a relativistic proton falls into a BH,all that happens is that the mass/energy/size of the evnthorizon increases by the rest mass of the proton, while the momentum ( kinetic energy part ) imparts an ever-so-slight acceleration to the BH, according to conservation laws.

 

A star moving around the galaxy or in response to the tug of another star does not stop moving after collapse.

[Sensei]

Let's see f.e. radioactive decay.

In one moment unstable parent isotope mass is contributing a bit to overall mass of Earth,

then when it decays part of that mass is changing to relativistic kinetic energy of alpha, proton, neutron, electron or positron (depending on decay mode).

If relativistic kinetic energy doesn't contribute to overall mass of Earth, it would means that masses of planets, stars and any objects in cosmic space are decreasing with time.

The more radioactive isotopes they have (with short half-lives), the more they would be losing mass. *)

Billions of billions of decays per second happens in Earth's core.

 

f.e.

Uranium-238 -> Thorium-234 + alpha + 4.26992 MeV

4.26992 MeV is equivalent to 7.6118*10^-30 kg mass lost per particle that decayed.

 

*) It happens evidently in decays where neutrino is escaping Earth with speed ~c.

 

[Strange]

Let's see f.e. radioactive decay.

In one moment unstable parent isotope mass is contributing a bit to overall mass of Earth,

then when it decays part of that mass is changing to relativistic kinetic energy of alpha, proton, neutron, electron or positron (depending on decay mode).

If relativistic kinetic energy doesn't contribute to overall mass of Earth, it would means that masses of planets, stars and any objects in cosmic space are decreasing with time.

 

That would only be true if the particles had sufficient kinetic energy to leave Earth. In general, as you say, that is only true for neutrinos (which don't carry much energy).

 

You might like this analysis: http://www.bbc.co.uk/news/magazine-16787636

One factor they take into account is the extra mass due to global warming.

[Enthalpy]

That thread confirms what I thought: relativistic mass does not increase gravitation (see post #6 for example).

 

I'm not willing to reopen here a topic already discussed there...

 

In a course, Pascal Picard explicitly rejects the Ricci tensor for the gravitation or moderate masses. Do what you want with that - I do nothing at all. I see that I asked the simplest case I could imagine (a reasonable double star) and got no answer, making me wary about more complicated arguments.

 

That's why I looked for simpler reasons and found the atoms with few and many protons, and the kinetic energy of electrons there. This kinetic energy increases the atom's inertial mass. Observation already tells us that it doesn't let carbon atoms fall more quickly to Earth than lead atoms do - that's within our experimental accuracy, and consistent with the principle of relativity. But if you want to believe something else, that's your problem, not mine.

[Strange]

I'm not sure what your point is. Both mass and energy contribute to gravitation. So, for example, a hot object will have more (a tiny amount more) gravitational mass than when it is cold, because of the kinetic energy of the atoms. I think we all agree on that. Don't we?