What are the different types of Mass?

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In summary: This usually only matters for subatomic particles, as they're the only things you'll encounter that move at anywhere near those speeds.At sufficiently high speeds (we're talking an appreciable fraction of the speed of light, so many thousands of kilometers per second, the kinetic energy of the object becomes so great that we have to include it in the mass, using Einstein's famous ##E=mc^2##. This usually only matters for subatomic particles, as they're the only things you'll encounter that move at anywhere near those speeds. (Be aware that this explanation is somewhat simplified. If you want to get the next level of detail down, you'll have to learn some relativity first. For now, suffice to say that
  • #1
Natsirt
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I've heard terms like solid mass,or maybe still mass and I'm sure there are others so can I get a little education?
 
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  • #2
Natsirt said:
I've heard terms like solid mass,or maybe still mass and I'm sure there are others so can I get a little education?

As far as physics and the equations like ##E_k=\frac{mv^2}{2}## or ##F=ma## are concerned, there's only mass, and adjectives like "solid" are irrelevant. In colloquial English, the word "mass" is also used to mean some lump of some sustance and then people say things like "solid mass" or "huge globular mass" and the like, but that has nothing to do with the ter as used in physics.
 
  • #3
OK I'm glad to hear its not as complicated as I thought it would be. So why are those Mass terms used in the first place?
 
  • #4
Natsirt said:
OK I'm glad to hear its not as complicated as I thought it would be. So why are those Mass terms used in the first place?

To be descriptive?
 
  • #5
Thanks Nugatory you have been very helpful.
 
  • #6
Natsirt said:
I've heard terms like solid mass,or maybe still mass

Can you give us quotations that show how these terms were used, in context? In particular, I've never heard of "still mass."

I wonder if these might be bad translations into English. If that is the case, seeing how they are used would help us tell you what the proper English terms are.
 
  • #7
jtbell said:
Can you give us quotations that show how these terms were used, in context? In particular, I've never heard of "still mass."

I wonder if these might be bad translations into English. If that is the case, seeing how they are used would help us tell you what the proper English terms are.


I'm sorry my knowledge on the subject is very little. I actually meant to say rest mass.
 
  • #8
Natsirt said:
I'm sorry my knowledge on the subject is very little. I actually meant to say rest mass.

"rest mass" is the mass of an object as measured by an observer who is at rest relative to the object.
 
  • #9
What is the difference between measuring a mass when your at rest relative to said mass and not being at rest relative to said mass?
 
  • #10
Natsirt said:
What is the difference between measuring a mass when your at rest relative to said mass and not being at rest relative to said mass?

At sufficiently high speeds (we're talking an appreciable fraction of the speed of light, so many thousands of kilometers per second, the kinetic energy of the object becomes so great that we have to include it in the mass, using Einstein's famous ##E=mc^2##. This usually only matters for subatomic particles, as they're the only things you'll encounter that move at anywhere near those speeds.
(Be aware that this explanation is somewhat simplified. If you want to get the next level of detail down, you'll have to learn some relativity first. For now, suffice to say that when physicists speak of the "mass" of an object, they mean the mass as measured by an observer at rest relative to the object, and sometimes they'll say "rest mass" just to reinforce that point)
 
  • #11
Natsirt said:
What is the difference between measuring a mass when your at rest relative to said mass and not being at rest relative to said mass?
When not at rest, you measure the mass to be higher. The greater the relative speed, the greater the mass.
More to be found here:
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html#c3


The two "kinds" of mass not mentioned so far are the inertial and gravitational mass.
The first one is the mass in Newton's 2nd law of motion ##F=ma##, and is the measure of resistance to having the state of motion changed. The more of it you have, the harder it is to accelerate you.
The second kind is both of the masses in Newton's law of gravitation ##F_g=GMm/R^2##. It's the measure of the "charge" inherent to an object, that produces gravitational field.
Turns out they are equal as far as we can tell(their equality has been measured to some ridiculous degree by now).
For the above reason, they're treated as one thing, but their equality is not something obvious or necessary.
 
  • #12
So when subatomic particles are going near the speed of light the amount of energy creates a measurable amount of more mass?
 
  • #13
You may find our FAQ https://www.physicsforums.com/showthread.php?t=511175 [Broken] helpful: it talks about "rest mass" and "relativistic mass".
 
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  • #14
Natsirt said:
So when subatomic particles are going near the speed of light the amount of energy creates a measurable amount of more mass?

You might want to think about what it would mean to measure the mass of a subatomic particle moving close to the speed of light - your question is more subtle than it looks at first glance.

But yes, it is true that a particle moving rapidly relative to me will accelerate differently when I apply a force to it than would the same particle at rest relative to me. From there, a naive application of Newton's ##F=ma## law would leave me with the conclusion that the mass is different. You will find this treatment in some obsolete textbooks and (sadly) in too much of the popular literature.

However, the modern understanding is that what you measure when the particle is at rest relative to you is the mass, we say "rest mass" occasionally to remind ourselves, and the funniness we get when we apply ##F=ma## to a particle moving at relativistic speeds should be treated as a relativistic correction to the momentum instead.

I have to say again: what I'm saying here is oversimplified to the point of being almost just plain wrong. Until you're ready to seriously study relativity, you can just say that there's just one mass, it's always the same whether the object is moving or not, and leave it at that.
 
  • #15
DrGreg said:
You may find our FAQ https://www.physicsforums.com/showthread.php?t=511175 [Broken] helpful: it talks about "rest mass" and "relativistic mass".


I found this helpfu . Very simplified, it sounds like energy warps spacetime because E=mc2 but a mass does not have to be solid to do so. In other words it can still pass through things. Is that right?
 
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1. What is the difference between mass and weight?

Mass is a measure of the amount of matter in an object, while weight is a measure of the force of gravity acting on an object. Mass is a constant property of an object, whereas weight can vary depending on the strength of gravity.

2. What is the difference between rest mass and relativistic mass?

Rest mass refers to the mass of an object when it is at rest, while relativistic mass takes into account the effects of motion and energy on an object's mass. Relativistic mass increases as an object's velocity approaches the speed of light.

3. What are the different types of mass in physics?

In physics, there are three types of mass: inertial mass, gravitational mass, and rest mass. Inertial mass is a measure of an object's resistance to changes in its motion, gravitational mass is a measure of an object's response to gravitational forces, and rest mass is the mass of an object at rest.

4. How is mass measured?

Mass is typically measured using a balance or scale. The standard unit of mass in the International System of Units (SI) is the kilogram (kg). Mass can also be measured indirectly through its effects on other objects, such as in the case of gravitational mass.

5. Can mass be created or destroyed?

According to the law of conservation of mass, mass cannot be created or destroyed, only transformed from one form to another. In other words, the total mass of a closed system remains constant over time.

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