Mass Energy: Understanding Total, Rest and Kinetic Energies

[pmb_phy]

As long as we talk about relativistic mass and total energy, mass and energy are equal, ...

Nope. That statement has been proven wrong. In fact Einstein wrote a paper which implied it was wrong early in his carreer (~1906). See above where I explained this. The expression E = mc^2 is invalid for a neutral atomic nucleus moving in a uniform E-field. I guess I should try to calculate the difference someday as another example of where it differs.

Best wishes

Pete

 

[pmb_phy]

Hi Pete,
Originally Posted by pervect: "relativistic mass" is another name for energy

Yes. I saw that. It is an incorrect statement.

But hey Pete, I think you missed that original statement by Pervect!

I miss all of his posts since I blocked him. He kept repeating himself with the same ole comments about certain things and he absolutely refused to work out our differences in PM. I have no time or patience with people with these qualities. Note that I'm not putting pervect down. Call it a clash of personalities. I have nothing against him myself.

Best wishes

Pete

 

[pervect]

Yes. I saw that. It is an incorrect statement.
I miss all of his posts since I blocked him. He kept repeating himself with the same ole comments about certain things and he absolutely refused to work out our differences in PM. I have no time or patience with people with these qualities. Note that I'm not putting pervect down. Call it a clash of personalities. I have nothing against him myself.

Best wishes

Pete

I'll invite our moderators or other science advisors here to express there opinion about which of us is correct, if they have an opinion on the matter.

Meanwhile, I am convinced that Pete is wrong, and I've attempted to not just state this as a personal opionion, but to provide some extensive quotes and references about why I think he is incorrect.

I'm also not particularly interested in exchanging PM's with him.

This is the first I've heard that Pete has his "fingers in his ears". I'm not quite sure what do to about that, it's news to me.

I don't have any particular personal animosity towards Pete, in fact I learned quite a number of things by arguing with him over the years. But I don't feel like recent conversations with him have been very productive for either of us - they may still continue to be of some use to people learning the topic, I suppose.

 

[Farsight]

Perhaps this might be a good time for me ask you guys about the relationship between rest mass, inertia, and momentum?

 

[lightarrow]

Perhaps this might be a good time for me ask you guys about the relationship between rest mass, inertia, and momentum?

I'll give you my answer, but someone will probably not agree with it.

1. Rest mass = m. Is the body's mass in its ref. frame.

2. Inertia. If you mean "inertial mass" then it is = m/SQRT[1 - (v/c)^2].

3. Momentum (linear momentum): p = m*v/SQRT[1 - (v/c)^2].

 

[Farsight]

Thanks lightarrow. I'll go with intertial mass.

I wanted to try to get things going again with a simple viewpoint relevant to the original question. Imagine I'm at rest in space, alongside my cannonball. We can talk about its rest mass, inertial mass, and momentum quite happily. There are no issues.

Now imagine I'm moving at 10m/s past the cannonball. However in my ignorance I think I'm stationary, and the cannonball is actually moving past me. The rest mass is still what it was. But as far as I'm concerned, the inertial mass is slightly different, and momentum is very different. I can even throw in kinetic energy, and say it's got some now when it didn't previously. But the object hasn't changed at all. Not one jot. It's still sitting there, happily doing nothing. Because these things are ways of relating my velocity to my the subject. They aren't actually there in the cannonball.

 

[pervect]

Thanks lightarrow. I'll go with intertial mass.

I wanted to try to get things going again with a simple viewpoint relevant to the original question. Imagine I'm at rest in space, alongside my cannonball. We can talk about its rest mass, inertial mass, and momentum quite happily. There are no issues.

Now imagine I'm moving at 10m/s past the cannonball. However in my ignorance I think I'm stationary, and the cannonball is actually moving past me. The rest mass is still what it was. But as far as I'm concerned, the inertial mass is slightly different, and momentum is very different. I can even throw in kinetic energy, and say it's got some now when it didn't previously. But the object hasn't changed at all. Not one jot. It's still sitting there, happily doing nothing. Because these things are ways of relating my velocity to my the subject. They aren't actually there in the cannonball.

What do you mean by "inertial mass"? And why do you care, i.e. why isn't knowing the rest mass, momentum, and energy of the cannonball "good enough"?

 

[Farsight]

I didn't mean to bring it up, pervect. Blame lightarrow. I was just trying to show that there's a variety of terms that we tend to think of as being some property of the actual object. You know, what is the momentum of the cannonball? and all that. But the cannonball is just sitting there. Nothing's happened to it. It hasn't moved, changed temperature, or anything. The property isn't in the cannonball. It's in my velocity, relative to the cannonball.

 

[lightarrow]

What do you mean by "inertial mass"?

I mean the term M which is multiplied to velocity v to give linear momentum p:
p = M*v, since F = dp/dt.

 

[pmb_phy]

I mean the term M which is multiplied to velocity v to give linear momentum p:
p = M*v, since F = dp/dt.

"What do you mean by inertial mass?" is a rather odd question since the term is almost universally used to refer to what some people call "relativistic mass" or just plain "mass."

Best wishes

Pete