
#19
Aug405, 10:21 PM

P: 214





#20
Aug405, 10:24 PM

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http://www.physicsforums.com/showpos...394#post688394 I've posted links to course notes using the same definition of inertial mass. 



#21
Aug405, 10:24 PM

P: 214





#22
Aug405, 10:26 PM

P: 214





#23
Aug405, 10:29 PM

Sci Advisor
P: 8,470

Just to be clear, are you claiming for sure that the inertia of a black box filled with gas won't appear to increase when the temperature increases, or are you just not certain either way? 



#24
Aug405, 10:33 PM

P: 214





#25
Aug405, 10:35 PM

HW Helper
P: 4,125

The rest mass of an object is the (total energy of the object in the rest frame)/c^2 This need not be the sum of the rest masses of the constituent particles. The rest frame is the frame where the center of mass of the object is at rest. 



#26
Aug405, 10:38 PM

Sci Advisor
P: 8,470

Here is another page (from mathpages.com, a pretty reliable internet resource) that says that the inertia of a composite object (its resistance to being accelerated) will be a function of its total energy, not just the energy of the rest mass of all the constituent particles: 



#27
Aug405, 10:40 PM

P: 214

Apparently you all need a little refresher course, I hope this helps.
The total energy of a particle is: [tex]E = \gamma m c^2[/tex] where [itex]\gamma[/itex] is the Lorentz factor, m is the particle's rest mass and c is the speed of light. We can also write: [tex]E = E_0 + K[/tex] where K is the particle's kinetic energy and [itex]E_0[/itex] is the particle's rest energy. That is: [tex]E_0 = m c^2[/tex] The relativistic kinetic energy is then easily seen to be: [tex]K = (\gamma  1) m c^2[/tex] which for [itex]\gamma[/itex] close to 1 (v << c) reduces to approximately [tex]K = 1/2 m v^2[/tex] the usual Newtonian expression for kinetic energy. 



#28
Aug405, 10:42 PM

P: 214





#29
Aug405, 10:49 PM

P: 214





#30
Aug405, 10:54 PM

Sci Advisor
P: 8,470

And aside from the issue of definitions, that mathpages.com page confirmed that the resistance to acceleration (inertia) of a composite object will be proportional to its total energy, so the inertia of a box filled with gas will increase as the gas is heated. Do you have any source that says otherwise? Have you actually done a calculation to see how a box filled with moving objects would react to external forces? If not, why are you so confident, when multiple sources say otherwise? 



#31
Aug405, 10:56 PM

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#32
Aug405, 10:59 PM

P: 214





#33
Aug405, 11:01 PM

P: 214





#34
Aug405, 11:03 PM

P: 214

If I have objects in my car moving at .9999999999999999999999999999999999999999999999c bouncing all over the place, what is the mass of my car?




#35
Aug405, 11:06 PM

Sci Advisor
P: 8,470





#36
Aug405, 11:08 PM

P: 214




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