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Television Sets Weighing More

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Efros
726259.  Wed Jul 07, 2010 8:18 am Reply with quote

The whole electron adding to the weight theory is attractive but erroneous. The TV has the same number of electrons in it whether it is on or off, it's just that when it's on they are moving.

 
Posital
726319.  Wed Jul 07, 2010 2:16 pm Reply with quote

dr.bob wrote:
Sadly for Posital, the Crookes radiometer does not turn due to the pressure of light.
Well I be jiggered - thanks for putting me right, bob. In my defence - I always thought it was in a vacuum. Ah well.

Nichols Radiometer.

 
dr.bob
726398.  Thu Jul 08, 2010 4:10 am Reply with quote

Efros wrote:
The whole electron adding to the weight theory is attractive but erroneous. The TV has the same number of electrons in it whether it is on or off, it's just that when it's on they are moving.


...and therefore have more energy, and therefore weigh more.

E=mc^2, dude! Not erroneous at all.

 
mckeonj
726412.  Thu Jul 08, 2010 5:24 am Reply with quote

Burglars report that TV sets are more difficult to move when plugged in and switched on.

 
Efros
726429.  Thu Jul 08, 2010 6:51 am Reply with quote

dr.bob wrote:
Efros wrote:
The whole electron adding to the weight theory is attractive but erroneous. The TV has the same number of electrons in it whether it is on or off, it's just that when it's on they are moving.


...and therefore have more energy, and therefore weigh more.

E=mc^2, dude! Not erroneous at all.


That would be the energy that would be released if all of the mass of the electron was converted to energy this is not related to the Kinetic Energy, which, due to the fact that electrons in a circuit move very slowly (can't remember the QI episode) is very very small. KE = 1/2mv^2, considering the mass of an electron is 9.10938188 10-31 kg, this coupled with a slow speed squared it multiplies out to not very much.

 
dr.bob
726444.  Thu Jul 08, 2010 10:27 am Reply with quote

It is related to the kinetic energy. It's related to any energy. E stands for "Energy", "not some particular types of energy but not others".

Note the original post on this thread mentions an increase in mass "however marginal". Just because the increase in mass is vanishingly small doesn't mean it's not real.

 
Efros
726445.  Thu Jul 08, 2010 10:37 am Reply with quote

It may well stand for energy, but the energy possessed by an electron cannot be equated to mass, this can only happen if the electron is travelling close to the speed of light, then you can use the relativistic Energy equation.

KE = mc^2-Mc^2 (M here is moree normally expressed as m subscript 0 and is the rest mass)

In any event electrons conducting current don't approach relativistic speeds.

 
Posital
726562.  Thu Jul 08, 2010 3:07 pm Reply with quote

Efros wrote:
In any event electrons conducting current don't approach relativistic speeds.
They'd have difficulty setting off a speed camera...

 
Efros
726594.  Thu Jul 08, 2010 4:49 pm Reply with quote

Even one set up specifically for Little Tike's cars.

 
dr.bob
726683.  Fri Jul 09, 2010 5:54 am Reply with quote

Efros wrote:
It may well stand for energy, but the energy possessed by an electron cannot be equated to mass


Yes it can. Any energy can be equated to mass, because it's all one and the same thing. That's the whole point of E=mc^2.

Efros wrote:
this can only happen if the electron is travelling close to the speed of light, then you can use the relativistic Energy equation.


How close? At what proportion of the speed of light do relativistic equations suddenly become valid? Where is this magical cut-off point? More importantly, how do the electrons know that they should suddenly stop obeying Newtonian mechanics and start obeying relativistic laws instead?

 
Efros
726687.  Fri Jul 09, 2010 6:27 am Reply with quote

Go ask Einstein, he specifically included terms that enabled the application of Newtonian mechanics to non relativistic speeds, and non-Newtonian mechanics when those speeds approached that of light.

 
dr.bob
726753.  Fri Jul 09, 2010 10:20 am Reply with quote

There's no such thing as a "non-relativistic" speed. Relativity applies to any speed. Einstein gave the equation of the relativistic mass of a body as:



Where v is the velocity, and m_o is the rest mass of the body.

Note the v^2/c^2 factor in there. That produces a non-zero result for any non-zero value of v. So even if an electron is moving at 0.0000001 m/s, it's still got a (albeit vanishingly small) relativistic mass and so is still heavier than if it's completely stationary.

 
Efros
726773.  Fri Jul 09, 2010 11:04 am Reply with quote

"non-relativistic speed"

 
Posital
726802.  Fri Jul 09, 2010 2:12 pm Reply with quote

Eh? - the concept of non-relativistic speed is simply something for lazy mathematicians/modellers...

(I like the idea of simply using a google-search as a reliable source. Great improvement over "a friend told me".)

 
dr.bob
727291.  Mon Jul 12, 2010 5:11 am Reply with quote

Quite so, Posital. The phrase "non-relativistic speed" simply means "speeds at which relativistic effects are so small, classical mechanics will give you a result that's close enough to reality for most calculations." It most certainly does not mean "speeds at which relativistic effects do not apply in any way, shape, or form" since the only speed for which that is true is zero.

 

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