Does heating an object increase its weight?

  • Thread starter MathematicalPhysicist
  • Start date
In summary, the conversation discusses the concept of mass in relation to the speed of light and how it is defined in modern relativity. It is clarified that mass does not increase with speed and it is an invariant quantity. The conversation also explores the idea of changing an object's mass by adding or subtracting energy. It is mentioned that heating an object can increase its mass, while cooling it can decrease its mass. An example is given using the atomic mass unit and Boltzmann k to calculate the change in weight of an iron cannonball when heated by 10 degrees. The conversation ends with a suggestion for a different unit system that would make calculations easier.
  • #1
MathematicalPhysicist
Gold Member
4,699
371
with the increase of a body's velocity to the speed of light (v->c) so does the body's mass increase m->infinity.
does this means that light has infinite mass? i know that light doesn't have rest mass because it never rests .

hope that my layman terms won't affect the answer.
 
Physics news on Phys.org
  • #2
Originally posted by loop quantum gravity
with the increase of a body's velocity to the speed of light (v->c) so does the body's mass increase m->infinity.
does this means that light has infinite mass? i know that light doesn't have rest mass because it never rests .

hope that my layman terms won't affect the answer.

Mass doesn't increase with speed. According to modern relativity it is invariant. And a photon has zero mass. The relation between energy and mass according to special relativity is
E^2 = (pc)^2 + (mc^2)^2
For a photon E = hf and p = h/lamda = hf/c.
This gives:
(hf)^2 = (hf)^2 + (mc^2)^2
m = 0.
It is only when the momentum of a massive particle is zero, p = 0 that it gives the popular result
E = mc^2.
 
  • #3
i was under the impression that when you acclerate a matter up to the speed of light the mass of the body increases, thanks for correcting me.
 
  • #4
Originally posted by loop quantum gravity
i was under the impression that when you acclerate a matter up to the speed of light the mass of the body increases, thanks for correcting me.

Thats an old paradigm introduced by Tolman, Lewis, and Plank, not Einstein who came to oppose it, that has no place in modern relativity. The modern definition of mass is such that it does not depend on speed. It is invariant.
 
  • #5
This thread has been edited in order to get it back on topic.
 
  • #6
Originally posted by DW
Thats an old paradigm introduced by Tolman, Lewis, and Plank, not Einstein who came to oppose it, that has no place in modern relativity. The modern definition of mass is such that it does not depend on speed. It is invariant.
so the mass of a body stays constant all the time? (i derived that from ivariant- doesn't change).
 
  • #7
Originally posted by loop quantum gravity
so the mass of a body stays constant all the time? (i derived that from ivariant- doesn't change).

Invariant and conserved mean two different things. An invariant thing does not change value with respect to velocity changes or in general in coordinate transformations. A conserved thing keeps the same value over time. The mass of an object is defined as its center of momentum frame energy divided by the square of the speed c. You can change the mass of an object over time simply by adding energy too it. Of course if you include the matter where that energy came from as a part of the system center of momentum frame energy and therefor mass will be conserved so whether the objects mass is conserved over time really depends on what you want to include as a part of the system defining the object.
 
  • #8
Originally posted by DW
Invariant and conserved mean two different things. An invariant thing does not change value with respect to velocity changes or in general in coordinate transformations. A conserved thing keeps the same value over time. The mass of an object is defined as its center of momentum frame energy divided by the square of the speed c. You can change the mass of an object over time simply by adding energy too it. Of course if you include the matter where that energy came from as a part of the system center of momentum frame energy and therefor mass will be conserved so whether the objects mass is conserved over time really depends on what you want to include as a part of the system defining the object.

"You can change the mass of an object over time simply by adding energy too it." -two questions: 1. the adding of energy will it increase the mass or decrease it? 2. the other way around of is substracting from the object energy and you can do so by freazing it then object looses energy but it doesn't affect the mass (so this is a bad example of substracting mass that will change the mass) can you give example of substraction of energy from object and as a consequence a change in the mass?
 
  • #9
Originally posted by loop quantum gravity
"You can change the mass of an object over time simply by adding energy too it." -two questions: 1. the adding of energy will it increase the mass or decrease it? 2. the other way around of is substracting from the object energy and you can do so by freazing it then object looses energy but it doesn't affect the mass (so this is a bad example of substracting mass that will change the mass) can you give example of substraction of energy from object and as a consequence a change in the mass?
By adding energy I do mean center of momentum frame energy. So, yes heating it up adds a minute amount of mass. Cooling it down subtracts mass from it. You may also remove mass simply by cutting a chunk off. It may also absord or emit latent energy in a phase change. You might also change the pressure at constant temperature.
 
  • #10
welcome DW


IIRC an atomic mass unit is about 930 MeV and
boltzmann k is about 8.6E-5 eV per kelvin
so we can even do an example
and see by how much the weight of an iron cannonball increases if it is heated by 10 degrees.

by what percentage, or ppm, or parts per billion, do I guess the weight would increase?

it would be so much nicer if an atomic mass unit were 1000 MeV
and Boltzmann k were a tenthousandth of an eV per kelvin,
a flat E-4 eV/K.

Then an iron atom of 56 mass units would be 56 GeV
and, since the heat capacity of a solid chunk of metal is about 3k per atom, raising temp by 10 kelvin would mean putting in about 30E-4 eV per atom

the fractional weight gain is whatever fraction 3E-3 eV is of 56GeV.
it looks like less than one tenth of a part per trillion.

So if Loop can supply a set of scales that can weigh accurate to one part in ten trillion, then we can demonstrate to him that heating an iron ball makes it heavier. and cooling it makes it lighter

this was meant as a friendly intrusion, you said everything necessary but I just felt sociable and chimed in
 

1. What is the best way to remember something?

The best way to remember something is to actively engage with the information. This can include taking notes, summarizing the material, or creating visual aids such as diagrams or flashcards. It is also helpful to practice retrieval by testing yourself on the information periodically.

2. How can I improve my memory for important information?

To improve your memory for important information, it is important to make meaningful connections with the material. This can involve relating the information to something you already know or creating associations with visual or auditory cues. It is also helpful to break the material into smaller chunks and review it regularly.

3. Is there a specific technique for remembering names and faces?

One technique for remembering names and faces is to repeat the person's name when you first meet them and try to make a connection between their name and a visual or verbal clue. For example, if you meet someone named Lily, you could visualize a bouquet of lilies when you see them. It is also helpful to pay attention to unique features about the person's appearance or characteristics.

4. Does stress affect memory?

Yes, stress can affect memory by impairing our ability to encode and retrieve information. When we are stressed, our brains release cortisol, which can interfere with the formation of new memories. It is important to manage stress levels and practice relaxation techniques to improve memory function.

5. Are there any foods or supplements that can improve memory?

While there is no magic food or supplement that can instantly improve memory, a healthy and balanced diet can support brain function. Foods that are rich in antioxidants, omega-3 fatty acids, and B vitamins have been shown to benefit memory. Additionally, regular exercise and proper sleep can also improve memory and overall brain health.

Similar threads

  • Special and General Relativity
Replies
11
Views
1K
  • Special and General Relativity
Replies
16
Views
2K
  • Special and General Relativity
2
Replies
45
Views
3K
Replies
130
Views
7K
Replies
21
Views
2K
  • Special and General Relativity
2
Replies
57
Views
4K
  • Special and General Relativity
Replies
5
Views
771
Replies
83
Views
4K
  • Special and General Relativity
2
Replies
55
Views
3K
  • Special and General Relativity
Replies
30
Views
2K
Back
Top